( ebook - pdf - eng) maya nurbs modeling 2 - tutorial

Using Maya: Modeling 207

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5 Creating and Editing Objects

This chapter introduces you to NURBS primitive objects. There are severalways you can use NURBS primitives to build objects quickly and easily. Useprimitives as a starting point, then use a combination of object and surfaceediting operations to complete a task.

Throughout this book you’ll find examples where primitives are used as thebase element of a particular task in combination with many of the Mayaediting and creation operations.

This chapter includes the following topics:

• “Using NURBS primitives” on page 207

• “Setting primitive options” on page 213

• “Editing objects in the Attribute Editor” on page 227

• “Using a construction plane” on page 232

• “Creating and editing text” on page 235

Using NURBS primitivesThe most basic object type is the primitive. Primitives are pure shapes thatcan be used as the basis of creating more complex models. You can createfive NURBS surfaces—Sphere, Cone, Cylinder, Cube, and Plane. You canalso create a Circle NURBS primitive that is a curve.

208 Using Maya: Modeling

Creating and Editing ObjectsUsing NURBS primitives

Creating objects with NURBS primitivesYou can instantly make simple NURBS objects like spheres, cubes, cylinders,cones, planes, and circles. When you select the NURBS primitive from themenu, it displays in all views at the origin of the grid (or ground plane).

By combining, transforming, trimming and cutting, or using surfacefunctions, such as filleting, on these simple shapes, you can construct morecomplex objects.

Modifying primitives to build objectsThere’s a fast and easy way to do almost anything in Maya, but using simpleprimitive shapes and the transformation tools Maya provides is the easiestway to build something that is simple, but essential to a scene.

For example, you can use a NURBS primitive cube to build a staircase. Yousimply scale it, duplicate it, and move each step into place.

Or you can select surface curves (isoparms) on two spheres, create a filletblend between them, and scale the spheres to create a bottle using a free-form surface fillet (Surfaces → Freeform Fillet).



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To create a simple animation, you can also select surface CVs, transformthem, and set key frames to the transformations.

First, select the CV or CVs you want to transform. Place the pointer over theactive object, then with the right mouse button select Control Vertex fromthe marking menu.

In this example, one CV of a NURBS primitive sphere is selected and movedusing the Move Tool.

You can also transform either one or multiple CVs from the Channel Box.Select the CV or CVs, then enter values in the X, Y and Z boxes provided.

The following shows the editable CV boxes in the Channel Box for a singleCV. The X value is changed and the CV is moved accordingly.



In the next example, multiple CVs are moved from the Channel Box.

You can then animate the CVs by setting keyframes.



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Using the Show Manipulator Tool with primitivesWhen you create a Sphere, Cone, or Cylinder NURBS primitive, you candisplay manipulators with which you can edit specific parameters of theprimitive.

To display these manipulators, make sure the primitive is created withhistory. Select the Show Manipulator Tool while it is active (or before youcreate it), then click the primitive’s heading in the Channel Box. You can alsoselect the primitive’s heading from the History menu in the Status Line orfrom the Inputs menu in the marking menu.

Editing primitives using revolve manipulatorsThe NURBS Sphere, Cylinder, and Cone primitives are like revolvedsurfaces, therefore the manipulators that display are revolve manipulators.

Circle Sweep manipulator

The circle at the bottom of the revolve manipulator is called the Circle Sweepmanipulator. Click-drag the manipulator handle to sweep the sphere, orenter values in the Numerical Input line or the Channel Box. You can alsoenter a new Sweep value in the options window before you create the sphere,or from the Attribute Editor after you create the sphere.

Important Note

You cannot animate CVs on an object that was created with history andthen delete the object’s history. The CV animation will not be correct andunexpected results will occur.



AxisStartPoint and AxisEndPoint manipulators

The arrow manipulator handles represent the origin and direction of theaxis: AxisStartPoint and AxisEndPoint. Click-drag these handles toreposition the axes. You can also enter values in the Numerical Input linewhile a manipulator is active or in the Location Attributes section of thesphere’s Attribute Editor.

axisMidPoint manipulator

The axisMidPoint handle represents the pivot point position. Click-drag themiddle handle, or enter values in the Numerical Input line or in theAttribute Editor.


Creating and Editing ObjectsSetting primitive options

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Setting primitive optionsSince most of the options for primitives are similar, the option descriptionsfor the Sphere NURBS primitive are described in detail. A table is includedafter the options window illustration for subsequent NURBS primitives. Ifthere are options which are not common to all primitives, they are alsodescribed in detail.

To set primitive options:

1 Select the type of primitive you want to create and click the box (❐) from themenu to open the options window(Primitives → Create NURBS → Sphere - ❐).

2 To change the option settings, immediately after the primitive is created,select Edit → Undo. Change the options, then press the Create button tocreate a new primitive.



Setting the default pivot point

Pivot By default, the Pivot is set to Object, and the resulting primitive is created atthe origin. The primitive appears centered about the specified pivot; therotate and scale pivots of the primitive are at the origin.

For example, Sphere, Cone, and Cylinder primitives are revolved fromsimple hidden curves and this option defines the start point of the axis ofrevolution.

If you set Pivot to User Defined, you can enter values in the Pivot Point X,Y, and Z boxes to reposition the primitive. The resulting primitive iscentered about this point.

Changing the direction of the X, Y, and Z axes

Axis Select either X, Y, or Z (Y is the default) to change the axis direction of theobject.

Axis Definition If you select the Free button, the X, Y and Z Axis Definition boxes areenabled. Enter new values to change the axis direction in X, Y and Z.

Changing the sweep angle

Start and EndSweep Angles

Enter the degree of rotation about the vertical world axis. Degree values canrange from 0.00 to 360.00 degrees. The default is 360.00 degrees, whichcreates a full 360 degree of revolution. The following example shows the topview of a sphere after changing the End Sweep Angle to 180 degrees (ahemisphere).

See also “Editing primitives using revolve manipulators” on page 211 forinformation about the Circle Sweep manipulator.

Default = 360 End Sweep Angle = 180



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Changing the radius value

Radius Enter a value in the Radius box or use the slider to change the radius.

Changing the surface degree

Surface Degree Select a Surface Degree option to automatically create the NURBS sphere asa Linear (degree 1) or a Cubic (degree 3) B-spline. The default is Cubic.

Controlling the accuracy of the sphere using tolerance

The more sections and spans, the better the match. When you create aNURBS Sphere primitive, the sphere is always an approximation to a truesphere. In some cases you may want to build a surface that matches a truesphere to a certain tolerance. When you specify the tolerance, Number ofSpans is automatically computed to be enough to be able to match a truesphere to the given tolerance.

Use Tolerance If Use Tolerance is toggled on, you can see the effects when you change thevalues in the Tolerance slider from the Attribute Editor. Set this tolerancevalue in the options window before you create the sphere only if you knowthe values you need.

If set to None, no tolerance calculations are performed and the sphere iscreated with the given number of sections and spans. This is the default.

If set to Local, the following is displayed:

Cubic Linear



You can enter a new value to override the Positional tolerance value you setin Options → General Preferences → Modeling.

Local tolerance is useful on a per-task basis where you want to change thesevalues, but don’t want to change the Global tolerance values.

If set to Global tolerance, the Positional tolerance value you set inOptions → General Preferences → Modeling is used.

Subdividing the sphere

Number ofSections

The Number of Sections value specifies the number of subdivisions that arecreated on the sphere. The default value is 8. The following shows a spherewith 16 sections. A value less than 4 gives a poor approximation to a sphere.

You can also change the number of sections in the Channel Box or theAttribute Editor.

In the Channel Box, click the makeNurbSphere heading and enter a newvalue in the Sections box.

Sections = 8 (default) Sections = 16



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In the Attribute Editor, click the makeNurbSphere tab to open the SphereHistory section of the editor, then enter a new value in the Sections box.

Changing the number of spans

Number ofSpans

Enter a value in the Number of Spans box to increase the number of spansthat define a primitive. A value less than 4 gives a poor approximation to asphere.

You can also change the number of spans in the Channel Box or theAttribute Editor.

In the Channel Box, click the makeNurbSphere heading and enter a newvalue in the Spans box. In the Attribute Editor, click the makeNurbSpheretab to open the Sphere History section of the editor, then enter a new valuein the Spans box.

Number of Spans = 4 (default) Number of Spans = 16



Setting Circle optionsSelect Primitives → Create NURBS → Circle - ❐ to open the optionswindow.

Common option descriptionsThe following table refers you to the documentation for each option.

Option Heading and page

Pivot “Setting the default pivot point” on page 214

Normal Axis “Changing the direction of the X, Y, and Z axes” onpage 214

Sweep Angle “Changing the sweep angle” on page 214

Radius “Changing the radius value” on page 215

Degree “Changing the surface degree” on page 215



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Setting Cylinder optionsSelect Primitives → Create NURBS → Cylinder - ❐ to open the optionswindow.

The NURBS Cylinder primitive is created as an open-ended cylinder.

Changing the height to radius ratio

Ratio of Heightto Radius

Use the slider or enter a new value in the Ratio of Height to Radius box tochange the height to radius ratio of the cylinder.

Use Tolerance “Controlling the accuracy of the sphere usingtolerance” on page 215

Number ofSections

“Subdividing the sphere” on page 216




Common option descriptionsFor information on the other options, refer to the following table.



Axis “Changing the direction of the X, Y, and Z axes” onpage 214

Start/End SweepAngle

“Changing the sweep angle” on page 214


Surface Degree “Changing the surface degree” on page 215


Number ofSections


Number of Spans “Changing the number of spans” on page 217



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Setting Cone optionsSelect Primitives → Create NURBS → Cone - ❐ to open the optionswindow.

The NURBS Cone primitive is created as an open-ended cone.



Common option descriptionsThe following table refers you to the documentation for each option.




Start/End SweepAngle

“Changing the sweep angle” on page 214


Ratio of Height toRadius

“Changing the height to radius ratio” on page 219



Number ofSections


Number of Spans “Changing the number of spans” on page 217



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Setting Cube optionsSelect Primitives → Create NURBS → Cube - ❐ to open the optionswindow.

A NURBS Cube primitive consists of six separate sides. You can click toselect a side of the cube in the view, or click on a heading in the Outliner orHypergraph window (Window → Outliner or Hypergraph).



To select the cube as a whole object, select the top heading in the Outliner orHypergraph window, or click the Select by hierarchy and combinationsicon from the Status Line.

Changing the cube’s width

Width Enter a value in the Width box to change the default value or use the sliderto change the width of the cube.

Changing the length and height ratios

Ratio ofLength to Width/ Height to Width

Enter a value in the Ratio of Length to Width or Height boxes to change thedefault value, or use the slider to specify the height and length of the cube.

Setting U and V patches

U patches/VPatches

Change the value in the U Patches or V Patches boxes or use the slider to setthe number of (U, V) patches between the edges that make up the cube. Thisvalue changes the number of spans on an object. You can also change thesevalues in the Channel Box or the Attribute Editor.



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Setting Plane optionsSelect Primitives → Create NURBS → Plane - ❐ to open the optionswindow.







Changing the length ratio

Ratio of Lengthto Width

Enter a value in the Ratio of Length to Width box to change the defaultvalue, or use the slider to specify the length of the plane. You can alsochange these values in the Channel Box or the Attribute Editor.





Width “Changing the cube’s width” on page 224


U/V Patches “Setting U and V patches” on page 224


Creating and Editing ObjectsEditing objects in the Attribute Editor

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Editing objects in the Attribute EditorTo edit an object after you create it, use the Attribute Editor. To open theAttribute Editor for an active object, either:

• Click the option box (❐) in the Object pop-up menu in the Channel Box.

• Click the option box (❐) in the History list menu on the Status Line.

• Click the option box (❐) in the Inputs pop-up menu in the marking menu.

• Select Window → Attribute Editor.

The following is the Attribute Editor for a NURBS primitive Sphere. TheAttribute Editor for NURBS primitives include the same options andattributes you find in the options window. Click the makeNurb tab for aselected primitive (for example, makeNurbSphere) to see these attributes.See the options window descriptions for details.



Sphere History

The Sphere History section of the editor gives you access to the options youset in the options window. You can change these options to adjust the finalresult after the primitive is created.

Location Attributes

The Location Attributes are used to change the X, Y, and Z position of thepivot and the direction of the axes.

Accessing the surface history sections of the editorClick the second arrow beside the heading to access the primitive’stransform and shape tabs. Click a tab to open that section of the editor andaccess the information you need.

NURBS Surface History

The NURBS Surface History section of the editor (the nurbsSphereShape tab)lists the statistical information for the active primitive. This information isread-only; it simply provides you with the primitive’s geometric data.

Click this arrow to access the transform and shape tabs.



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Click the triangle beside a heading to open that section of the editor.

Model Stats

The following shows the Model Stats section for a NURBS primitive sphere.You can change these attributes to alter the sphere’s display.



If you want to change the parameters of a rendered primitive or adjust thetessellation parameters if you converted it to polygonal output, click thetriangles to open those sections of the editor.

Object Display

The Object Display section lets you toggle the visibility of the primitive on oroff, or turn it into a templated or intermediate object. For example, you canmake a primitive invisible to used as a guide for subsequent operations.

Bounding Box

The Bounding Box section under Object Display is read-only. It displays theminimum and maximum world space coordinates of a primitive along the X,Y and Z axes.

Transforming an object in the Attribute EditorClick the nurbsSphere tab to open the transformation section of the editorfor a NURBS sphere.



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Transform Attributes

The Transform Attributes section lets you enter values to move, rotate, scale,or shear the primitive. You can change the X, Y, Z rotation order or rotatethe local axes.

Pivots

Use the Pivots section to change the position of the scale or rotate pivots,and toggle the display of scale and rotate pivots on or off.

Limit Information

Use the Limit Information section to set limits to the transformations of theprimitive. You toggle the Limit X, Y, or Z boxes on or off and then changethe values in the transformation boxes. When you transform the primitive,you can now only move, rotate, or scale to the unit value you set in thecorresponding boxes.

Display

In the Display section, you can toggle the display of the local axis, display aselection handle, set a default manipulator (if you use the Show ManipulatorTool on an object), or hide the whole object or toggle it into a template.

Tip

As an alternative, use Modify → Transformation Tools and select MoveLimit Tool, Rotate Limit Tool, or Scale Limit Tool.


Creating and Editing ObjectsUsing a construction plane

Using a construction planeUse Primitives → Construction Plane to create an infinite planeperpendicular to the Z axis, passing through the origin (the X Y plane, whichis the default). This type of plane differs from a NURBS primitive planebecause you cannot render or animate it. You use these planes asconstruction aids. By default, a construction plane is created as a 24 x 24 unitsquare.

You can use a construction plane as a live construction surface (click theMake Live icon on the Status Line or select Modify → Make Live).

A live construction plane replaces the ground plane as the surface on whichpoints are placed when using one of the curve creation tools, or on whichobjects are moved relative to. By transforming the plane, planar curves canbe created in arbitrary planes.



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Setting Construction Plane OptionsSelect Primitives → Construction Plane - ❐ to open the options window.

Before you create a new construction plane, change the options, if necessary,then click the Apply button.

Creating a construction plane at a specified location

Pole Axis The Pole Axis determines the orientation of the construction plane. Thedefault is an YX plane.

Determining the size of the construction plane

Size Enter a value in the Size box or use a slider to specify a size for the newconstruction plane.

YX YZ XZ



Transforming the construction plane

You can use the transformation tools to move, scale, and rotate theconstruction plane. Since you cannot, however, select a live object, either:

• transform the plane before you make it live,

• toggle the live plane off, select it and transform it, then make it live again

Editing the construction plane in the Attribute EditorThe Attribute Editor for a construction plane contains generic attributes youuse to transform and alter the display of the plane. See “Editing objects inthe Attribute Editor” on page 227 for details.


Creating and Editing ObjectsCreating and editing text

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Creating and editing textUse Primitives → Create Text to create text objects and control theircharacteristics. A wide selection of fonts are available.

To create text:

1 Select Primitives → Create Text.

2 The word Maya is displayed at the origin (0, 0, 0) by default.

To create your own text curves, open the options window, type the text youwant to create, select a specific font, and the type of text you need. See thefollowing for details.

Setting Create Text optionsSelect Primitives → Create Text - ❐ to open the options window.



Entering new text and changing the font

Text Curves options let you alter the text string in a number of ways. Afteryou select your options, click the Create button to see the resulting text.

To change the text:

1 Select Primitives → Create Text - ❐ to open the options window.

2 Type a new word in the Text box.

3 Select the Font and set the Type options, then click the Create button.

Tip

The options only affect the active text string in the text field. Text that hasalready been placed is not affected.



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To change the font and create the new text:

1 Click the arrow beside the Font box to select a different font from the menu.

2 Press the Create button. The new text appears at the origin in the font youselected.The following shows the word Magic in an AvantGarde-Book font.

Transforming textThe text that first appears at the origin when you select Create Text is activeby default. Text are curves, which means they are separate entities. All thecurves for one text string are grouped under one transform.The transformresults can vary depending on the way you select the text.



To transform the text later (after you deselect the text then perform anotheroperation and reselect it), you will find that the letters are not transformedtogether.

To transform a text string:

If you want to transform a whole string of existing text, the transformationwill occur on each letter individually if you marquee-select the text. Totransform the whole string, do the following:

1 Marquee-select the letters. Notice the headings in the Channel Box. The leadobject, (the c in Magic), is the only curve that appears while the other lettersare individual curves.

2 Change some of the values in the Channel Box. In this example, the X, Y, andZ Scale values are changed. Notice that all letters are scaled, but the spacebetween the letters is lost.



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To correct this problem, select Edit → Undo, deselect the text, then changethe selection type. Click the Select by hierarchy and combinations icon andreselect the text.

or

3 Open the Outliner window (Window → Outliner) and select the top textobject (Text_Magic_1).



4 The heading in the Channel Box now displays the text string as one object(Text_Magic_1), and all the letters are displayed in the lead object color.

5 You can now transform the whole string as one object.

To transform individual letters:

1 If you want to transform just one letter in a text string, open the Outlinerwindow (Window → Outliner).

2 The letters in a text string are grouped under a parent node calledText_Magic_1. Click the triangle beside this heading to display theindividual letters and select the one you need. The Channel Box is updatedand the letter is highlighted in the view.



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Changing the text type

Type The three Type buttons, Curves, Trim, and Poly, are used to create text inthree different formats. Select one of these before you create the text.

The Curves text type is the default. The text is displayed as NURBS curveswhich you can transform and manipulate.

The Trim text type is created as planar trim surfaces. This means that theseletters will render because they are surfaces.

The Poly text type is created as polygons which you can manipulate as youwould any other polygonal entity. When this text type is selected, a planartrim curve is created between the curve and tessellate nodes, but you onlysee the polygonal surface, not the planar surface.

Notice the difference between a Trim text string and a Poly text string in theHypergraph (Window → Hypergraph).

Planar trim surfaces

Polygonal surfaces



Editing the text in the Attribute EditorThe Attribute Editor for text curves contains the same transform attributes asyou would find for curves. See “Transforming curves in the AttributeEditor” on page 80 for details.


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6 Introduction to Surfaces

This chapter introduces you to using Maya surface functions. In this chapteryou will learn some basic surface construction rules and how easy it is toconvert NURBS surfaces to polygonal surfaces.


• “What is world coordinate space?” on page 243

• “What is an isoparm?” on page 245

• “What is the U / V surface direction?” on page 246

• “What is a surface normal?” on page 248

• “What is construction history?” on page 250

• “Converting NURBS to polygons” on page 252

What you need to know about surfacesWith Maya surface creation and editing tools and actions, you can editexisting surfaces using a variety of methods. You can also use curves asconstruction guides to create more organic surfaces. The following explainssome of the concepts you need to know about surfaces.

What is world coordinate space?You build objects in a 3D coordinate system that lets you define objectsusing dimensionally accurate values. In Maya, the origin is the center. Theorigin’s coordinates are 0, 0, 0. All points are defined by one coordinate inthe X direction, one in the Y direction, and one in the Z direction.

A Y-up world is defined by the viewing plane which displays X ashorizontal, Y as the up direction, and Z as the depth of the scene. This is thedefault XYZ orientation.


Introduction to SurfacesWhat you need to know about surfaces

A Z-up world starts with a ground plane that represents the X and Ydirections, and Z represents the up direction. To illustrate, put your middlefinger on your nose (Y), point your thumb out (X) and point your indexfinger up (Z).

To change the Y-up or Z-up orientation, select Options → GeneralPreferences and select an Up Axis button from the World CoordinateSystem section of the window.

X

Y

Z



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What is an isoparm?A parametric surface is crossed with flow lines, or isoparms. Isoparms areconstant U or V parameter curves on a surface.

The flow lines on a surface are drawn at parameter values that correspond tothe locations of edit points on the surface’s edge curves. The regionsbetween these isoparms are called patches.

The interval between two edit points on a surface edge is called a span.

The number of patches on a surface is equal to the number of spans in Umultiplied by the number of spans in V. The more spans on a surface, themore CVs.

Tip

Keep the number of patches to a minimum. The fewer patches you have,the more control you have.

isoparms

U V

patch

span



What is the U / V surface direction?The U/V coordinate system is similar to the X, Y, and Z coordinate systemused to position objects. The difference is that it applies to points that liedirectly on the surface. In some ways, the U and V directions are likelatitude and longitude.

Where curves have a single U parameter, surfaces have an additional Vparameter. Just as the value of U varies along the length of a parametriccurve, both U and V vary across a parametric surface. Any point on a surfaceis defined by a U and V value.

Understanding U/V parameter space is important when you are drawingcurves on surface or when you are positioning textures on a surface.

The parameter direction is determined in various ways. For example, for arevolved surface, the U parameter direction of the surface is determined bythe construction curve, and the V parameter direction is determined by thedirection of the revolve.

What are U and V divisions?U and V divisions are visual aids and do not change the geometry of asurface. You change the division values to see a finer wire mesh, but thenumber of spans stays the same. You can change these values in the ModelStats section of the Attribute Editor.

Construction

Revolved

curve in U

surface in V



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This example shows what happens when you change the division values fora NURBS primitive sphere.

Changethesevalues

3 divisions in U 3 divisions in V 3 divisions in U and V



What is a surface normal?A surface normal is a vector that is perpendicular to the surface at a givenpoint. For example, surface normals are used to calculate the way lightreflects from the surface.

What is the surface normal direction?The direction of U and V on the surface determines the direction of thesurface normal. To illustrate, point your right thumb in the increasing Udirection and your right forefinger in the increasing V direction, then pointyour middle finger perpendicular to these two to see the surface normaldirection.

The direction of surface normals can be very important when rendering. Forexample, if you render a hollow object, you can render either the inside orthe outside. If the normals point outward, the outside is rendered. To renderonly the inside, you can reverse the normals to point inward.

To display surface normals:

1 While the object is active, select Display → NURBS Components →Custom- ❐.

2 In the Display Control Options window, toggle Normal (shaded mode) onand click the Apply button.

U

VNormal



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3 Make sure you select a Flat Shade or Smooth Shade mode from the Shadingmenu in the current view to see the normals.

How to reverse the surface normal directionIn some situations, you may need to reverse the direction of the surfacenormals. Use Edit Surfaces → Reverse Surface to do this.



Open the Reverse Surface options window (Edit Surfaces → ReverseSurface - ❐) and change the options if necessary.

• Reversing the direction of U or V reverses the surface normal direction.

• Reversing both U and V does not change the surface normal direction.

• Swapping U and V reverses the surface normal direction.

See “Reversing the curve or surface direction” on page 195 for details.

In the following example, a NURBS cone’s surface normals are reversed.Instead of pointing outward, the normals are pointing inward.

What is construction history?If you create surfaces using construction history, the original curves remainlinked to the new surface. This means that editing the original constructioncurves also edits the surface. You can also connect surfaces with multiplelevels of history, which means if you edit one construction curve, severalsurfaces can be affected.

Tip

Some situations require U and V to be aligned in specific directions. Forexample, when applying a parametric texture map, the mapping of theimage to a surface depends on the U / V orientation. If a texture mapappears inverted on the surface, reversing the U / V direction of thesurface is one way to correct the problem.



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You can create surfaces without history by selecting the ConstructionHistory icon from the Status Line before you create the surface.

You can also delete history once a surface is created. While the surface isactive, select Edit → Delete by Type or Delete All by Type → History.

See “Using construction history” on page 2 in Chapter 1, “NURBSModeling” for more information.

Tip

When you attach curves or animate CVs, turn Construction History off oryou may get unexpected results.


Introduction to SurfacesConverting NURBS to polygons

Converting NURBS to polygonsUse Edit Surfaces → NURBS To Polygons to convert NURBS surfaces topolysets. You can convert any NURBS surfaces created in Maya or importedsurfaces, including trimmed surfaces.

Use the options window to specify the resulting polygonal output, or youcan change the result in the Attribute Editor.

To convert NURBS geometry to polygonal geometry:

1 While a surface is active, select Edit Surfaces → NURBS To Polygons. Apolygonal representation of the surface is created on top of the NURBSsurface.

2 The NURBS surface is still there. If you want to reconstruct the surface,select Edit → Undo to undo the polygonal surface, edit the NURBS surface,then select Edit Surfaces → NURBS To Polygons again.

Note

If you convert the surface while construction history is on, you can edit thesurface. The polygonal surface is recreated to match the edited NURBSsurface.



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Setting NURBS To Polygons optionsSelect Edit Surfaces → NURBS To Polygons - ❐ to open the optionswindow.

Outputting to triangles or quads

Type Use a Type option to specify the type of polygons to use when you convertNURBS geometry to polygonal data.

If you select Triangle (the default), 3-sided polygons are created.

If you select Quads, 4-sided polygons are created.

Quad polygon typeTriangle polygon type



Choosing a tessellation methodTessellate means that you create a set of polygons from NURBS geometry.Each tessellation method provides you with options that let you control theresulting polygonal surface.

There are three tessellation methods; Standard Fit, General, and Count.

Standard fitStandard Fit is the default tessellation method. It is “adaptive” tessellation,meaning that the following options are used to determine when to stop thetessellation.

For example, the tessellation stops at the Fractional Tolerance value you set.If there is an edge shorter than the Minimal Edge Length, the tessellationstops on that edge. If the surface is flat enough within the edge (the specifiedchord/height ratio is small enough), the tessellation stops there.

Chord HeightRatio

The Chord Height Ratio is the ratio between the maximum distance of thecurve from the polygon edge used to approximate it and the chord length.The chord length is the linear distance between two polygon vertices.

A value greater than 0 results in fewer polygon vertices, if the ratio on thecurve is greater than the current value. For example, the default value, 0.1,means that the height must be larger than 1/10 of the chord length beforeadditional edit points are created.

FractionalTolerance

The Fractional Tolerance value determines the degree of accuracymaintained between the original surface and the interpolated polygonalsurfaces. The default is to be accurate to within 0.01 units, where a unitrefers to the current unit of linear measure (the default unit of measure iscentimeters). Therefore, at no point will the polygonal surface be more thanthe tolerance distance away from the original NURBS surface.

Minimal EdgeLength

Enter a value or use the Minimal Edge Length slider to set the minimumlength of the edges of the triangles or quads that are created.

Note

When you tessellate a trimmed surface, some 3-sided (triangle) polygonsmay be created along the trim edge even when the option is set to Quads.



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3D Delta The 3D Delta value determines the 3D spacing for U and V isoparms on asurface that makes up the initial grid for the tessellation. In the followingexample, the 3D Delta value is changed from the default 0.1 to 0.01.

GeneralSet the Tessellation Method to General to display the following options.

3D Delta=0.1 3D Delta=0.01



Setting the initial tessellation controls

Unless Use Chord Height or Use Chord Height Ratio is toggled on, auniform tessellation is performed. Each span/surface is split into a numberof polygons depending on the Number U and V values you set.

U Type/V Type The U Type and V Type pop-up menu items let you specify whether youwant to split the surface based on where the spans are (then split each span),or based on the parameterization of the whole surface.

Number U/Number V

Each span or surface is split into the number of polygons you specify here.

Specifying the chord height and chord height ratio

Chord Height/Chord HeightRatio

If Use Chord Height or Use Chord Height Ratio is toggled on, you can set aspecific value for both the Chord Height and the Chord Height Ratio. Avalue greater than 0 results in fewer polygon vertices if the ratio on thecurve is greater than the current value. For example, the default value, 0.1,means that the height must be larger than 1/10 of the chord length beforeadditional edit points are created.

If Edge Swap is toggled on the value you specify determines the optimumchord height method with which to tessellate a quadrilateral into triangles.

CountSet the Tessellation Method to Count to display the following slider.

Count Use the Count slider to determine how many polygons the surface can betessellated into. See the following examples.



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Editing the polygonal result in the Attribute EditorTo edit the attributes for NURBS geometry converted to polygonalgeometry, select the polygonal surface you want to edit and use theAttribute Editor.

To open the Attribute Editor, either:





The Attribute Editor changes depending on which NURBS surface youconverted to polygonal data. Some of the options you set in the optionswindow or the Channel Box are displayed. See the option descriptions fordetails (“Setting NURBS To Polygons options” on page 253).

Count = 200 Count = 100 Count = 50


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7 Creating surfaces

In this chapter you will learn how to create surfaces using various Mayaconstruction methods.


• “Filleting surfaces” on page 259• “Blending surfaces” on page 271• “Revolving surfaces” on page 279• “Lofting curves and surfaces” on page 293• “Beveling surfaces” on page 303• “Extruding surfaces” on page 316• “Preparing to stitch surfaces” on page 328• “Creating stitched surfaces” on page 328• “Stitching surface points” on page 339• “Creating boundary surfaces” on page 346• “Creating birail surfaces” on page 356

Filleting surfacesFillets let you quickly create an object with rounded edges, or blend twosurfaces together. Three methods are provided: circular filleting, free-formfilleting, and blending fillets.

Creating circular surface filletsUse Surfaces → Circular Fillet to construct a fillet surface between twoexisting surfaces. The following example uses NURBS primitives to quicklyand easily create a smooth rounded edge where the two objects join.

To create a circular surface fillet:

1 Create and scale NURBS plane primitive, then create and scale a NURBScylinder primitive. Since the cylinder is created at the origin by default,notice how it fits through the plane.


Creating surfacesFilleting surfaces

2 To create a circular fillet where the cylinder meets the plane, marquee-selectthe plane and the cylinder, then select Surfaces → Circular Fillet.

Setting Circular Fillet optionsSelect Surfaces → Circular Fillet - ❐ to open the options window.



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Creating trim curves

Create Curve OnSurface

Toggle Create Curve On Surface on to create curves-on-surface when thefillet is constructed. The curves are automatically placed on the surface at thepoint where they intersect with the fillet.

When Create Curve On Surface is off curves-on-surface are not constructedon the original surface. The default is off.

To trim the surface using fillet trim curves:

1 Before you create the fillet, toggle Create Curve On Surface on.

2 Select both surfaces and click the Fillet button. When the fillet is created,trim curves (or curves-on-surface) are displayed.

3 Deselect both surfaces.

4 Select Edit Surfaces → Trim Tool and click on the part of the surface youwant to keep. The fillet is trimmed away from the surface. Deselect thesurfaces again and use the Trim Tool to trim away from the other curve-on-surface.

Trim curves



Reversing the surface normals

ReverseSurface Normals

During the fillet construction, the surfaces are offset in the direction of thenormals by the Radius value you specify. By reversing the surface normals,you can exactly construct the desired fillet. Click the Show Manipulator iconto see the surface normals.

Before you create the fillet, choose to reverse either the primary surfacenormal (the first selected surface), or the second surface normal (the secondselected surface). The following examples show both primary and secondaryreverse methods with a radius value of 0.75.



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To reverse surface normals by selecting surface points:

You can also reverse surface normals by selecting points on the surfaces andthen constructing the fillet. For example, the normals on the secondarysurface are reversed if the point selected on the primary surface does not lieon the same side as its surface normal.

1 Select Surface Point from the marking menu while a surface is active. Clickto select a point, then Shift-select another surface point.

circular fillet Reverse Primary

Reverse Secondary Reverse Primary, Secondary



2 Select either Reverse Primary Surface Normal or Reverse SecondarySurface Normal, then click the Fillet button. Click the Show Manipulatoricon to see the surface normals.

Editing the circular fillet normals using manipulators

1 To display the surface normals and radius manipulator, select the ShowManipulator Tool after you create the fillet.

2 Click-drag a radius manipulator handle. You can also click on an activemanipulator and enter a value in the Numerical Input line, or enter a valuein the Channel Box.

Defining the circular surface fillet’s tolerance

Use Tolerance The Use Tolerance options let you reapply a circular fillet within a specifiedtolerance value. You can apply tolerance globally or locally.

Global tolerance means the Positional and Tangential values you set inOptions → Preferences → Modeling are used.



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If you select Local, you can enter a new value to override the Positional andTangential tolerance value you set in the General Preferences optionswindow. Local tolerance is useful on a per-task basis where you want tochange these values, but don’t want to change the Global tolerance values.This is the default.

Editing circular surface fillets in the Attribute EditorTo edit a circular filleted surface, use the Attribute Editor. To open theAttribute Editor, either:







The Attribute Editor for circular filleted surfaces contain the same attributesyou find in the Circular Fillet options window. See the option descriptionsfor details.

Creating free-form surface filletsUse Surfaces → Freeform Fillet to construct a fillet between two curves-on-surface, two surface isoparms, or trimmed edges.

To create a free-form surface fillet between two isoparms:

You have to select two isoparms to create the free-form surface filletbetween.

1 Click the Select by component type icon.

2 With the right mouse button, click the Lines icon and toggle Isoparms onfrom the pop-up menu.



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Place the pointer over the active surface, and use the right mouse button toselect Isoparm from the marking menu.

3 Shift-click the two isoparms you want to create a free-form fillet between,then select Surfaces → Freeform Fillet.

To create a simple object, such as a cocktail shaker, select the top of thesurface, then scale the top smaller than the bottom. Notice how the filletadjusts accordingly to the transformation.



To create a free-form surface fillet between curves-on-surface:

Select the curves-on-surface, then select Surfaces → Freeform Fillet.

Editing the free-form fillet using manipulators

1 Click the Show Manipulator icon, then perform the free-form fillet.

2 To display specific isoparm manipulators, click the heading that you needfrom the Channel Box and change the values in the Min and Max boxes.

You can also enter values in the Numerical Input line while a manipulator isactive and press Enter.



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Setting Freeform Fillet optionsSelect Surfaces → Freeform Fillet - ❐ to open the options window.

Changing the free-form surface fillet’s bias and depth

Bias The Bias value scales the end tangents across the two surface curves.

Depth The Depth value controls the curvature of the filleted surface.

Defining the free-form surface fillet’s tolerance

Use Tolerance The Use Tolerance options let you reapply a free-form fillet within aspecified tolerance value.

If you select Global tolerance, the Positional and Tangential value you setin Options → General Preferences → Modeling are used.

If you select Local, you can enter a new value to override the Positional andTangential tolerance value you set in the General Preferences optionswindow.

Local tolerance is useful on a per-task basis where you want to change thesevalues, but don’t want to change the Global tolerance values. This is thedefault.



Choosing the output geometry

OutputGeometry

Select either Nurbs or Polygons for the output geometry type. NURBSsurfaces are created by default. See “Converting NURBS to polygons” onpage 252 for more information on the Polygons options.

Editing free-form surface fillets in the Attribute EditorTo edit a free-form filleted surface, use the Attribute Editor. To open theAttribute Editor, either:





The Attribute Editor for free-form filleted surfaces contain the same optionsyou find in the Freeform Fillet options window. See the option descriptionsfor details.


Creating surfacesBlending surfaces

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Blending surfacesUse the Surfaces → Fillet Blend Tool to build a surface by forming a blendbetween two boundaries defined as a set of surface curves.

If you know which options to set before you create the blended surface, openthe options window first, then use the tool to create the surface. Click theoption box (❐) after the tool name to change the option settings. See “SettingFillet Blend Tool options” on page 274 for details.

Alternately, you can create the blended surface with the default options andthen edit the completed surface from the Channel Box or Attribute Editor.See “Editing the blend fillet using manipulators” on page 273 and “Editing ablended surface in the Attribute Editor” on page 278 for details.

To construct a blended surface:

In the following, you transform a sphere and cone NURBS primitive andcreate a fillet blend between them to create the head of a bird.

1 Create and translate a sphere and a cone NURBS primitive so that thecircular isoparm of the cone (the bottom) is facing the bottom of the sphere.

The following illustration shows the primitives in the top view. Notice howthe bottom of the cone and the sphere are placed so that the isoparms onboth objects are facing each other.

2 Deselect both surfaces and select Surfaces → Fillet Blend Tool.

3 In the side view, click on the first surface isoparm and press Enter.



4 Click on the second surface isoparm and press Enter to create the fillet blend.

5 If necessary, click-drag to reposition the isoparm before you press Enter tocreate the blend.

6 When the isoparm is in the desired position, Shift-click on the originalisoparm to deselect it.

You can now transform either the cone or the sphere. The fillet blend adjuststo the transformation. In the following illustration, the head of the bird onthe left is scaled larger, and on the right the beak is scaled smaller.



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Editing the blend fillet using manipulators

1 Click the Show Manipulator icon before or after you perform the filletblend.

2 To display both manipulators and editable parameters for the resulting fillet,click the ffBlendSrf heading in the Channel Box.

Note

If you want to use the manipulator handles to adjust a fillet blend, try notto use straight lines as the selected isoparms (such as the edges of twoplanes). Twisting and unexpected results may occur.



3 To display specific isoparm manipulators, click the heading that you needfrom the Channel Box and change the values in the Min and Max boxes.

You can also enter values in the Numerical Input line while a manipulatorhandle is active.

Setting Fillet Blend Tool optionsSet the tool options before you blend the surfaces. To open the optionswindow, select Surfaces → Fillet Blend Tool - ❐.



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To change the options after the blend is completed, use the Channel Box orthe Attribute Editor. See “Editing a blended surface in the Attribute Editor”on page 278 for details.

Setting the blend direction

There are three possible blends for the same input—First, Second, and Firstand Second.

Automatic BlendDirection

The Automatic Blend Direction calculates which one works best. Thisoption is toggled on by default.

If Automatic Blend Direction is toggled off, the Flip Boundary Normalsoptions are displayed.

Flipping the boundary normals

These options are used to determine the boundary normals by flipping thecurve around to create a different fillet blend.

First If First is toggled on, the surface for the first selected isoparm is flippedresulting in different surface normals.

Second If Second is toggled on, the surface for the second selected isoparm isflipped resulting in different surface normals.

If both First and Second are toggled on, both normals are flipped.



If Automatic Blend Direction is toggled off and you use the ShowManipulator Tool, additional locators are displayed. Click a manipulatorhandle to flip the surface normals.

Defining the fillet blend’s tolerance

Tolerances Click the Tolerances triangle to display the tolerance settings. These optionslet you apply a fillet blend within a specified tolerance value. You can applytolerance globally or locally.

If you select Global tolerance, the Positional and Tangential value you setin Options → General Preferences → Modeling are used. This is thedefault.

First

First and Second

Second



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If you select Local, you can enter a new value to override the Positional andTangential tolerance value you set in the General Preferences optionswindow. Click the Local button to display the following options

Local tolerance is useful on a per-task basis where you want to change thesevalues, but don’t want to change the Global tolerance values.


OutputGeometry




Editing a blended surface in the Attribute EditorTo edit the completed blended surface, open the Attribute Editor. To openthe Attribute Editor, either:





The Attribute Editor for a blended surface contains the same surface historyattributes for an object. See “Editing objects in the Attribute Editor” on page227 for details.


Creating surfacesRevolving surfaces

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Revolving surfacesUse Surfaces → Revolve to construct a surface by revolving a profile curveabout an axis. Any curve can be revolved: free curves, surface curves(isoparms), curves-on-surface, and trim boundaries are all valid. The curvecan be revolved by either positive or negative amounts, up to a maximum of360 degrees.

To revolve a curve to build a surface:

1 Draw a curve in the front view so it is perpendicular (Y) in the perspectiveview. This curve serves as the outline of the surface you want to construct.This is called the profile curve.

2 While the curve is active, select Surfaces → Revolve to build the surface.

U

V



3 When the surface is first created, the revolve history node is active. Click theShow Manipulator icon to see the revolve manipulators. If you want to editthe surface later, you have to select the revolve node in the Channel Box ormarking menu (from the Inputs menu) to see the manipulators. You can alsoedit the parameters for a completed revolved surface in the Attribute Editor.

Using the revolve manipulatorThe revolve manipulator consists of handles that let you interactively changethe pivot and direction of the revolve axis, and the end sweep angle of therevolve.

Using the axis manipulatorsClick the Show Manipulator icon before or after you create the revolvedsurface to display the revolve manipulator.

Tip

By default, all selected curves are revolved 360 degrees about the world Yaxis. The U parameter direction of the surface is determined by the originalcurve. The V parameter direction is determined by the direction of therevolve. See “What is the U / V surface direction?” on page 246 for moreinformation.

Make sure construction history is on before you create a revolved surface ifyou want to use the Show Manipulator Tool to edit the resulting surface.

AxisMidPoint

AxisEndPoint

AxisStartPoint

CircleSweep



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Click-drag the handles to change the axis of revolution of the revolvedsurface interactively, or enter exact X, Y, and Z positions for the activehandle in the Numerical Input line. You can also enter precise values in theoptions window, Channel Box, or in the Attribute Editor.

The following shows what happens to the revolved surface when youtransform the axis manipulators.

Using the circle sweep manipulatorTo modify the sweep angle, drag the circle sweep manipulator by movingalong the arc, allowing the sweep to begin somewhere away from the profilecurve. You can also modify the sweep angle by changing its value in theChannel Box.

Tips

If you move the axis endpoints, the axis direction is modified. However, ifyou move the axis midpoints, the radius of the revolved surface ismodified without affecting the axis direction.

To snap the axis, start, end, and midpoint to the desired position, use asnap mode. The snap mode icons are located on the Status Line.

See the Basics book for more information about the Show ManipulatorTool.

Move the AxisEndPoint Move the AxisMidPointMove the AxisStartPoint



Editing the input profile curveIf construction history is on when the revolved surface is created, you canmodify the profile curve. This in turn modifies the completed surface. Whenyou select the profile curve, the surface changes color to indicate that it hasconstruction history.

If you have trouble selecting the profile curve, open the Hypergraph or theOutliner and select it from there (Window → Hypergraph or Outliner).

Note

You cannot use snap modes with the sweep manipulators.

Click-drag thesweep manipulator



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To transform the profile curve, you can either:

• use a transformation tool,

• change its properties in the Channel Box or Attribute Editor,

• use another operation, such as Extend or Detach Curves.

The following example shows the profile curve extended and scaled.



You can also display the connections for the revolved surface in theHypergraph window. Select Options → Show → Shape Nodes, click therevolve node (revolve1, for example), then click the Up and DownstreamConnections icon.

Profile curve extended Profile curve scaled

Select Shape Nodes, then click this icon.



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Setting Revolve optionsSelect Surfaces → Revolve - ❐ to open the options window.

Selecting the X, Y, or Z axis of revolution

Select an Axis Preset option to specify the revolution axis. The default is Y.

Axis Preset If you set the Axis Preset to X, Y, or Z, you cannot change the values in theAxis boxes. See “Setting a free axis of revolution” on page 286 for moreinformation about the Free option.

In the following example, a profile curve (drawn in the front view) isrevolved using each revolution axis in the perspective view.



Setting a free axis of revolution

Free Axis If you set the Axis Preset to Free, you can enter values in the Axis X, Y, or Zboxes to specify the axes about which the profile curve is revolved. You canalso change these values in the Channel Box or the Attribute Editor. In thisexample, 1 is the value for X, Y, and Z in the Channel Box.

Revolved in X

Revolved in Y (default) Revolved in Z

Profile curve



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Changing the pivot point location

Pivot If you set Pivot to Object, the revolve is performed from the default pivotlocation (0,0, 0). This is the default.

If you select Preset, you can change the X, Y, or Z location of the pivot pointby entering values in the Pivot Point boxes. You can also change thesevalues in the Channel Box or Attribute Editor.

The following shows how a revolved surface is created with the defaultpivot values and what happens when you change the default values to 5 inX, Y, and Z in the Channel Box.

Selecting the surface degree

Surface Degree The Surface Degree options determine whether the V parameter direction ofthe surface is created with linear (degree 1) or cubic (degree 3) geometry.

If you select Linear, the surface is constructed with flat facets all around.

If you select Cubic, the smooth polygonal profiles are defined by the originalprofile curve. This is the default.

0, 0, 0

5, 5, 5

by default



You can also change these values in the Channel Box or the Attribute Editor.To select a Degree type from the Channel Box, place the pointer in theDegree box, use the right mouse button and click-drag to select an optionfrom the pop-up menu.

Sweeping the revolved surface

Use the Start Sweep Angle and End Sweep Angle values to specify theangle of revolution in degrees. The default is 360, with a valid range of 0 to360. You can also change the sweep angle in the Channel Box or theAttribute Editor. See also, “Using the circle sweep manipulator” on page 281for information on how to sweep the revolved surface with manipulators.

Setting the revolve tolerance value

Use Tolerance The Use Tolerance options control the accuracy of the resulting revolvedsurface. You can apply tolerance globally or locally.

If you select None you can change the segments value. See “Defining thenumber of revolution segments” on page 289 for details.

If you select Local, enter a new value to change the tolerance of the revolvedsurface. This lets you create the revolved surface so it is closer to the actualsurface of revolution.

CubicLinear



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Global tolerance means the Positional and Tangential value you set inOptions → General Preferences → Modeling are used.

Defining the number of revolution segments

Segments The Segments value determines how many sections are used to create thesurface of revolution. With a sweep of 360 degrees, six or eight sections areusually sufficient. The following shows the revolve with the default 8sections.

You can also change the amount of sections in the Attribute Editor or theChannel Box. The following shows a surface with 20 segments, or sections.



If Use Tolerance is not set to None, the Segments value is automaticallycomputed so that the result differs from the default revolved surface by lessthan the specified tolerance value.

If Local is set as the Use Tolerance option, the tolerance value of therevolved surface is closer to the actual surface of revolution.

Selecting the curve range

Curve Range Select Complete as the Curve Range to create the revolved surface along theentire profile curve. This is the default.

Select Partial if you only want to use a segment of the curve for the revolve.

Editing part of the revolved surface

If you set the Curve Range to Partial before you create the revolved surface,a subCurve node is created. Use this node to specify a range of the curve.

To edit this curve range, select the subCurve node and click-drag the curvesegment manipulator (click the subCurve heading in the Channel Box, thenselect the Show Manipulator Tool) or change the Min and Max values.

Tip

If animating the sweep angle, change the Segments value instead of thetolerance value to change the numbers of CVs of the surface.



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OutputGeometry


To change the number of polygons created for the surface when creatingpolyset data, use the Attribute Editor. The polygonal surface must beselected. Click the nurbsTesselate tab to display and edit the TessellationAttributes and the Mesh Component Display.

Editing the revolved surface in the Attribute EditorTo edit the revolved surface, use the Attribute Editor. To open the AttributeEditor, either:







The options you set in the options window or the Channel Box aredisplayed. See the option descriptions, “Setting Revolve options” on page285 for details.

Input Curve The Input Curve information is read-only. It gives you access to the historyof the curve you used to create the revolved surface. Click the arrow buttonsto select the curve and open its section of the editor.

Editing the subCurves in the Attribute Editor

If you set the Curve Range to Partial in the options window when therevolve was created, you have access to the Attribute Editor for the resultingsubCurves. See “Setting SubCurve Attributes” on page 20 in Chapter 1,“NURBS Modeling” for details.


Creating surfacesLofting curves and surfaces

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Lofting curves and surfacesUse Surfaces → Loft to construct a surface that passes through a series ofprofile curves. These curves can be curves-on-surface, surface isoparms, ortrimmed edges. Lofting is used most often to create new surfaces fromcurves or primitive shapes, or to close open surfaces.

To loft curves:

1 Pick the first curve you want to loft, then Shift-click to pick subsequentcurves.

2 Select Surfaces → Loft.

3 The lofted surface is constructed from curve to curve in the order that youselected them. The last curve selected is green by default.

Tip

Before you begin, you need at least two profile curves or surface isoparms.

Tip

If you require an even and uniform transition of the surface as it loftsthrough each profile curve (for example, a boat hull), space the curvesevenly.



To add additional curves to a lofted surface:

You can add new curves to an existing lofted surface created withconstruction history.

1 Select one of the curves you used to create the lofted surface. Notice thelofted surface is displayed in the construction history color.

2 Select the curve you want to add, then select Surfaces → Loft.

The following shows the result when two curves are added to the initiallofted surface.



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To loft surface isoparms:

1 While the surface is active, click the Select by component mode icon.


or

While the pointer is positioned over the active surface, use the right mousebutton to select Isoparm from the marking menu.

3 Shift-click to select the isoparms you want to loft together, then selectSurfaces → Loft.



Setting Loft optionsSelect Surfaces → Loft - ❐ to open the options window.

Changing the loft parameterization

Select one of the Parameterization options to modify the V parameterizationof the lofted surface.

Uniform With Uniform knot spacing, the profile curves run parallel to the Vdirection. The parameter values of the resulting surface in the U directionare equally spaced. The first profile curve corresponds to the isoparm on thesurface at U 0, 0, the second to U 1.0, and so on.

Chord Length With Chord Length spacing, the parameter values on the resulting surface inthe U direction are based on the distance between the start points of theprofile curves.



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Changing the loft degree

Surface Degree You can set the Surface Degree to either Linear or Cubic. This sets the loftedsurface to linear or cubic in the U direction.

Reversing the loft direction

Auto Reverse If Auto Reverse is toggled off, the curves are used as they are which mayresult in a twisted surface. If toggled on, the curves are automaticallyreversed. The default in on.

In the following example, the two top curves and the two bottom curves aregoing in different directions.

Tips on Knot Spacing

Since lofting is based on the parameter values along the curves, if thecurves are all parameterized the same way (each curve is the same degreewith an equal number of edit points and identical knot values), the loftedsurface will have the same number of spans in the U surface parameterdirection. This helps to control the amount of surface data, and the size ofthe related data file. You can achieve this by copying the original crosssectional curve, and then transforming and modifying it as necessary.

If the parameterization of all the curves do not match, the resulting surfacecan have considerably more spans than any of the curves used in itsconstruction. If you create the original curves as Edit Point curves withchord length, this results in increased surface complexity.

Cubic Linear



If Auto Reverse is toggled off, the result is a twisted lofted surface. Iftoggled on, the curves are automatically reversed.

If Auto Reverse is toggled off, you can use the Show Manipulator Tool toreverse the curve direction of the original profile curves as needed. Simplyclick the manipulator handle to reverse the curve direction.

Opening or closing the lofted surface

Close The Close option determines whether the created surface is closed in the Udirection. Close is toggled off by default.

Auto Reverse onAuto Reverse off



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Curve Range If you set the Curve Range to Complete, the lofted surface passes throughthe entire curve.

If you select Partial and select the Show Manipulator Tool, curve rangemanipulators are displayed on the profile curves. This means you can dragthe manipulators to interactively alter the portion of the curve to use in theloft. The resulting surface only passes through the selected portions of theprofile curves (the subCurves).

Editing part of a lofted surface

To edit part of a lofted surface, set Partial as the Curve Range in the optionswindow. Click the Show Manipulator icon to display the curve rangemanipulators and editable parameters in the Channel Box. Click thesubCurve heading in the Channel Box for the input curve you want to edit.

Close toggled off Close toggled on

Click the subCurve

Click-drag themanipulators or entervalues in the Min/Max

heading in theChannel Box todisplay the manipulators

boxes.

for a specific subCurve.



You can also enter values in the Numerical Input line while a manipulatorhandle is active.


OutputGeometry



Editing the lofted surface in the Attribute EditorTo edit the lofted surface, use the Attribute Editor. To open the AttributeEditor, either:







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If you selected curves to construct the lofted surface, the following isdisplayed:

The options you set in the options window or the Channel Box aredisplayed. See the option descriptions for details.

Input Curves The Input Curve sections and available options change depending on whichmethod you used to create the lofted surface. This information is read-only.It gives you access to the history of the lofted surface you constructed. Clickthe arrow buttons to select the surface, isoparms, or curves and open itssection of the editor.

Reverse Curve If you toggle Auto Reverse off, a Reverse Curve toggle box is displayed foreach curve, primitive, or surface isoparm you used to create the loftedsurface. Select the Show Manipulator Tool to also display the reversemanipulators. Click the toggles to reverse the direction of the input curves,or click the manipulators.



In the following illustration, the first curve used to create the lofted surfaceis selected for reversal.


If you set the Curve Range to Partial in the options window when the loftwas created, you have access to the Attribute Editor for the resultingsubCurves. See “Setting SubCurve Attributes” on page 20 in Chapter 1,“NURBS Modeling” for details.


Creating surfacesBeveling surfaces

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Beveling surfacesUse Surfaces → Bevel to create an extruded surface with a beveled edgefrom any curve, including text curves and trim edges.

To create a beveled surface from a curve:

Click on the curve you want to bevel and select Surfaces → Bevel. Thefollowing example shows a text curve beveled with the default options.

To create a beveled surface from an isoparm:

1 To select the isoparms, click the Select by component type icon from theStatus Line.


or

While the pointer is positioned over the active surface, use the right mousebutton to select Isoparm from the marking menu.

3 Click to select an isoparm.



4 Select Surfaces → Bevel to bevel the isoparm.

Changing the bevel’s dimensions interactivelyYou can change the dimensions of the bevel interactively with the ShowManipulator Tool, or in the Numerical Input line. You can also enter valuesin the Channel Box or the Attribute Editor.

If you want to edit the beveled curve from the Channel Box or AttributeEditor, the manipulators do not have to be displayed.

Note

By default, Bevel Width and Bevel Depth are 0.5 linear units of measure,and Extrude Height is 1.00 linear units of measure.



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Editing a beveled curve with manipulatorsIf you bevel a curve, the following manipulators are displayed when youclick the Show Manipulator icon and click the bevel heading in the ChannelBox.

To interactively edit the bevel units, click-drag the manipulator handles. TheFeedback Line displays the current measurement of each bevel unit as youmove an active manipulator. You can also enter values in the NumericalInput line or in the Channel Box.

Changing the bevel height

The HeightPoint manipulator handle corresponds to the Extrude Depthoption in the Channel Box. To change the bevel height, click-drag theHeightPoint manipulator handle. You can also enter a value in theNumerical Input line or in the Extrude Depth box in the Channel Box.

HeightPoint

WidthPoint

DepthPoint



Changing the bevel width

To change the bevel width, click-drag the WidthPoint manipulator handle.You can also enter a value in the Numerical Input line or in the Width box inthe Channel Box.

Changing the bevel depth

To change the bevel depth, click-drag the DepthPoint manipulator handle.You can also enter a value in the Numerical Input line or in the Depth box inthe Channel Box.

Reversing the bevel direction

To reverse the direction of the bevel, use a negative value for the beveldepth, width, and height (or Extrude Depth). Change these values in theChannel Box or in the options window.

The following shows a beveled isoparm created in the default direction, andone in the reverse direction. Sometimes, this is the result you may want. Forinstance, you may want to create a beveled edge on a surface as shown inthe example.



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Editing a beveled isoparm with manipulators

Although the same manipulators are displayed for a beveled isoparm, anadditional set of manipulators, StartParam and EndParam, become availablewhen you click the isoparm heading in the Channel Box.

Click-drag the start and end parameter manipulators to change the beveledisoparm segment. You can also enter values in the Numerical Input line or inthe Min and Max boxes in the Channel Box. The following shows whathappens when you edit the StartParam.

Defaultdirection

Reverseddirection

Click to displayStart and Endmanipulators StartParam

EndParam



Setting Bevel optionsSelect Surfaces → Bevel -❐ to open the options window.



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Attaching the bevel surfaces

Attach Surfaces Toggle Attach Surfaces on to attach each part of the bevel surface. Thedefault is on. If toggled off, the surfaces are not attached.

For example, if Attach Surfaces is toggled off and you create a bevel withBevel set to Both, three surfaces are created. These surfaces are independentand can be selected and modified as such.

You can select one of these surfaces from the Hypergraph or Outlinerwindow (Window → Hypergraph or Outliner).

Attach Surfaces on Attach Surfaces off



You can also select the surface you want to edit from the Objects pop-upmenu in the Channel Box and open its Attribute Editor.

Selecting a bevel surface area

Bevel The Bevel options specify whether the beveled surface area is applied to thetop, bottom, or both sides of the original curve or isoparm. The followingexample uses a NURBS Circle primitive curve using each method.

The bevel is created from the top of the circle.

Top Side

The bevel is created from the bottom of the circle.

Bottom Side

The bevel is created from both the top andbottom of the circle. This is the default method.

Both



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Changing the bevel dimensions from the options window

You can enter exact bevel dimensions values before the bevel is created.

Bevel Width The Bevel Width value specifies the initial width of the bevel as viewedfrom the front of the curve or isoparm.

Bevel Depth The Bevel Depth value specifies the initial depth of the bevel portion of thesurface.

Extrude Height The Extrude Height value specifies the height of the extruded portion of thesurface, not including the bevel surface area. For more information, see:

• “Editing a beveled curve with manipulators” on page 305

• “Editing a beveled isoparm with manipulators” on page 307

• “Editing a beveled surface in the Attribute Editor” on page 314

Selecting a bevel corner type

Bevel Corners The Bevel Corners options specify how corners in the original constructioncurves are handled in the beveled surface.

Tip

The combination of Bevel Width and Bevel Depth values determine theangle of the bevel.

Only the extrude part of the bevelsurface is created.

Off

Straight

The bevel is created with linear, or straight, corners.



Selecting bevel cap edges to determine the bevel shape

Bevel Cap Edge The Bevel Cap Edge options are used to determine the shape of the beveledpart of the surface.

Setting the curve range

Use the Curve Range options if you are creating a bevel from a curve.

Note

If the curve is degree is 1 or 2, the bevel’s surface will be cubic (degree 3).

Circular Arcs

The bevel is created with rounded, or circular arc corners.

Convex

The bevel is created with a convex edge.

Concave

The bevel is created with a concave edge.

Straight

The bevel is created with a straight edge.



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Curve Range Select Complete to use the entire curve for the bevel operation. Complete isthe default setting.

Select Partial to only use a segment of the curve for the bevel. When youselect the Show Manipulator Tool, a manipulator is displayed at each end ofthe curve. Use these manipulators to edit a part of the input curve to changethe beveled result.

Editing part of the beveled curve

Select Partial as the Curve Range in the options window and click the ShowManipulator icon to display the curve range manipulators and editableparameters in the Channel Box.

Click the subCurve heading in the Channel Box for the input curve you wantto edit, then click-drag the StartParam or EndParam manipulator handles tointeractively edit the input curve. You can also enter values in the Min andMax boxes.

You can adjust these subCurves in the Attribute Editor if you require furthermodifications. See “Editing a beveled surface in the Attribute Editor” onpage 314, and “Editing a beveled isoparm with manipulators” on page 307for more details.


OutputGeometry


Setting the bevel tolerance

Use Tolerance The Use Tolerance options let you create a bevel within a specified toleranceof the original input curves. You can apply tolerance globally or locally.



Global tolerance means the Positional value you set in Options → GeneralPreferences → Modeling is used.

If you select Local tolerance, you can enter a new value to override thePositional tolerance value you set in Modeling Preferences.

Local tolerance is useful if you want to change these values often, but don’twant to change the Global tolerance all the time.

Editing a beveled surface in the Attribute EditorTo edit the completed beveled surface, use the Attribute Editor. To open theAttribute Editor, either:







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The options you set in the options window or the Channel Box aredisplayed. See“Changing the bevel’s dimensions interactively” on page 304and “Setting Bevel options” on page 308 for details.

Input Curve The Input Curve information is read-only. It gives you access to the historyof the curves or isoparms you used to create the bevel surface. Click thearrow buttons to select the curve and open its section of the editor.


If you set the Curve Range to Partial in the options window when the bevelwas created, you have access to the Attribute Editor for the resultingsubCurves. See “Setting SubCurve Attributes” on page 20 in Chapter 1,“NURBS Modeling” for details.


Creating surfacesExtruding surfaces

Extruding surfacesUse Surfaces → Extrude to construct a surface by moving a cross sectionalprofile curve along a path. Extrude works by sweeping a profile curve.Before you extrude, set the pivot point of each profile curve to specify therelationship between the profile and the path.

The profile curve, the curve you want to extrude along the path, can be anopen or closed free curve. You can also use a surface isoparm, curve-on-surface, or a trim boundary.

To create an extruded surface:

You need at least two curves to create an extruded surface: a path curve and aprofile curve. The profile curve is the curve that gets swept along the pathcurve to create the surface. The path curve is the last selected curve.

1 Select the profile curve first, then Shift-select the path curve. The last curveyou select (the path curve) displays in the selected default green color.

2 Select Surfaces → Extrude.

Tip

If you select more than two curves, select all the profile curves first, thenselect the path curve last.

Path curve

Profile curve



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To extrude a profile curve without using a path curve, change the extrudeStyle to Distance in the options window. See “Choosing the extrude style”on page 317 for details.

Setting Extrude optionsSelect Surfaces → Extrude - ❐ to open the options window.

Choosing the extrude style

Select a Style option to specify the type of extrusion you want. See “Settingthe extrude distance” on page 318 for information on the Distance option.

Flat If you choose the Flat option, the extrude maintains the orientation of thecross section in space as it moves along the extrusion path.

Restrictions

If the extrusion path has sudden changes of direction, undesirable twistingof the cross section around the path can occur. If this happens, increase thenumber of CVs in the path to make the change of direction between CVsmore gradual. Sharp corners work well, but tight corners do not. Forexample, try extruding a circle along a linear path with 90 degree angles.



Tube Tube is the default extrude style. It sweeps the cross section along thespecified path so that the reference vector stays tangent to the path.

Setting the extrude distanceSelect the Distance extrude Style to extrude a profile along a straight line.No path curve is required. When selected, the options window changes toinclude the following:

Extrude Length Enter a value or drag the slider bar to specify the length of the extrusion. Bydefault, the extrude length is 1.0. The following shows the result when youchange the value to 5.0.

With Tube, the extrusionsweeps along theprofile curve andpushes out as itfollows the path.



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Setting the profile normal extrude direction

Direction If Distance is the selected extrusion Style, the default direction of theextrusion is Profile Normal. This means that the direction of the path isautomatically taken from the normal of the profile curve. If the profile curveis not flat (planar), the average normal is used.

Specifying the direction vector

Direction Vector Click the Specify button to change the default direction for the extrusion.

Length = 1.0 Length = 5.0

Normal direction Resulting surface



When you click Specify, you can select X Axis, Y Axis, Z Axis, or Free. Ifyou select an axis button, the extrusion occurs along that axis. For example,if you click the Z Axis button, the extrusion will be linear in the Z direction.

If you select Free, you can enter values in the X, Y, and Z boxes to specify avector to extrude. For example, the extrusion occurs by 1.0 in the X directionby default. The following example shows what happens if you set X and Y to0.0 and Z to 1.0 when you extrude a curve.

Selecting the result position

Result Position If you set Style to Flat or Tube, At Profile is the default Result Position.This means the resulting surface starts at the profile; the path curve is movedto the profile and then the extrusion is performed.

If you select At Path, the profile curve is moved to the path curve and thenthe extrusion is performed. This results in a surface at the path.

Setting the pivot

Pivot The Pivot options are only available if you set the Style to Tube.

The Pivot options let you choose the pivot point method to position theprofile curve on the extrusion path. If you select At Path as the ResultPosition, you can choose the profile curve and position it to the pivot pointon the extrusion path.

If you choose Closest End Point, the path end point closest to the center ofthe bounding box of the profile curves is used. This end point is used as thepivot point for all the profile curves. If performing a multiple extrusion, theresulting surfaces are offset from the path. This is the default.

If you select Component, the pivot point of each individual profile curve isused to extrude the profile curve. The extrusion occurs along thecomponents of the profile curve.

x = 1.0y = 0.0z = 0.0

x = 0.0y = 0.0z = 1.0



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See the following examples.

Selecting the extrusion orientation

Orientation The Orientation options are only available if Style is set to Tube.

If you choose Path Direction, the direction of the extrusion is determined bythe direction of the path curve.

Closest End Point

Component

Path and profile curves



By default, the direction of the extrusion is determined by the ProfileNormal direction. The direction of the linear path is automatically takenfrom the normal of the profile curve.

Orientation examples

The following examples show the extrusion using a combination ofOrientation modes and Result Positions.

In this first example, Result Position is set to At Profile and Orientation isset to Profile Normal. The path curve is moved and rotated to match theprofile curve. This is the default setting.

In this next example, Result Position is set to At Path and Orientation is setto Path Direction.



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In this last example, Result Position is set to At Profile and Orientation isset to Profile Normal. The profile curve is moved and rotated to match thepath curve.




Curve Range Set the Curve Range to Complete to extrude the entire profile along theentire path.

Select Partial to extrude only part of the profile along part of the path. Thiscreates a “subCurve” history node (initially set to the whole curve) whichcan then be edited using the Show Manipulator Tool.

Editing the extruded surface using manipulators

If the Curve Range is set to Partial in the options window, you can use theShow Manipulator Tool to edit the parameter range of part of the curve usedin the extrude operation.

In the first example that follows, Tube requires two input curves, so twosubCurve history nodes are included in the Channel Box.

Click the heading in the Channel Box to select a subCurve history node, thenclick the Show Manipulator icon to display the manipulators (if not alreadyselected). Drag the manipulators to edit the subCurve interactively, or entervalues in the Min and Max boxes. In the following example, the profileinput curve (subCurve 1) is selected and edited.



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Now the path curve (subCurve2) is selected and edited.

If the Distance extrude style is used, click the extrude1 heading to displaythe manipulator to edit the length of the extruded surface.

Click the subCurve heading to edit the profile curve (the curve used tocreate the extrude).




OutputGeometry



Editing the extruded surface in the Attribute EditorTo edit the completed extruded surface, use the Attribute Editor. To openthe Attribute Editor, either:







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The Attribute Editor includes the options you set in the options window. See“Setting Extrude options” on page 317 for details.

Profile Curve/Path Curve

The Profile Curve and Path Curve boxes let you access the input curves aswell as statistical information about these curves. Click the arrows beside theboxes to select the input curves and click the tab to open the AttributeEditors for them.


If you set the Curve Range to Partial in the options window when theextrude was created, you have access to the Attribute Editor for the resultingsubCurves. See “Setting SubCurve Attributes” on page 20 in Chapter 1,“NURBS Modeling” for details.


Creating surfacesPreparing to stitch surfaces

Preparing to stitch surfacesUse Edit Surfaces → Prepare For Stitch to easily prepare multiple surfacesfor stitching before you use the Stitch Tool.

Prepare For Stitch attaches a stitch operation node in front of each selectedsurface. Any subsequent stitch or stitch surface points operation carried outon the surface is performed by using the stitch node inserted in front.

Creating stitched surfacesUse the Edit Surfaces → Stitch Tool to stitch, or align, two NURBS surfacestogether.

The two surfaces can be stitched together with position (C0) and tangent(G1) continuity. Stitch modifies the positions of the boundary row (column)of CVs, and the first row (column) of CVs on a NURBS surface to achieve C0and G1 continuity respectively.

If you know which options to set before you create the stitched surface, openthe options window first, then use the tool to stitch the surface. Click theoption box (❐) after the tool name to change the option settings. See “SettingStitch Tool options” on page 332 for details.

Alternately, you can create the stitched surface with the default options andthen edit the completed surface from the Channel Box or Attribute Editor.See “Editing the stitched surface in the Channel Box” on page 334 and“Editing the stitched surface in the Attribute Editor” on page 336 for details.

C0 (position) aligns the first CVsalong the surface isoparms.

G1 (tangent) uses the second CVsto achieve tangent continuity alongthe surface isoparms.

C0 continuity C0 and G1 continuity


Creating surfacesCreating stitched surfaces

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To stitch a surface:

1 Change the Stitch Tool options, if necessary. Click the option box (❐) besidethe tool name to open the options window.

2 Select Edit Surfaces → Stitch Tool, then follow the prompts on the HelpLine.

3 Select the isoparms you want to stitch together. The isoparms you selectmust be the surface boundary isoparms or the stitched surface is not created.Surface boundary isoparms are those that define the edges of a surface.

4 A temporary stitch surface is created. At this point, you can click-drag themanipulators to edit the stitch before you press Enter to see the resultingsurface.

5 Press Enter to complete the stitched surface.

Note

For illustrative purposes the following example displays in white. Mayadisplays this temporary stitch surface in bright green.



Selecting different edges

The stitch result depends on the order in which you select the surfaceboundary edges, provided the two edges have been assigned non-equalweights. See “Determining the weighting factors for the input isoparms(edges)” on page 333 for information on assigning weights on inputisoparms.

The following shows how the resulting surface is affected when you changethe selection order for the default edge weights of 1.0 and 0.0 on the first andsecond selected edge of a revolved surface. The highlighted isoparmindicates the first isoparm selected.



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Using isoparm manipulators on a stitched surface

You can also use manipulators to interactively edit the surface after it isconstructed. Select the Show Manipulator Tool and click on an isoparmheading in the Channel Box. The manipulators are displayed on the surfacefrom which you first picked the isoparm. Use these manipulators toselectively modify the portions of the two isoparms where the two surfacescome together in C0 and (or) G1.

Note

When you use the Stitch Tool, the manipulator displays only on edges witha non-zero weight.



Setting Stitch Tool optionsSet the tool options before you use the Stitch Tool. To open the optionswindow, select Surfaces → Stitch Tool - ❐.

To change the options after the surfaces are stitched, use the Channel Box orthe Attribute Editor. See “Editing the stitched surface in the AttributeEditor” on page 336 for details.

Setting the blend options

Blending Toggle the Blending options on or off to specify the global blend when thesurface edges are stitched.

Position is the default blending option. When selected, the two surfacesstitched together have positional continuity (C0).

When Tangent is selected, the two surfaces stitched together have tangentcontinuity (G1).



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Determining the weighting factors for the input isoparms (edges)

WeightingFactor on Edge

Before stitching the edges, the two selected isoparms are averaged in aweighted mode. The two surfaces are modified to meet along this averagedisoparm in C0, G1. You can assign weights to the selected isoparms.

By default, a weight of 1.0 and 0.0 is assigned to the first and second selectedisoparm. In effect, this modifies the CVs on the second surface so the surfaceis C0, G1 continuous with the first surface. If you assign a non-zero weightto the two selected isoparms, the CVs on both surfaces are modified toachieve C0, G1 continuity.

You can choose to modify the weights after completing the stitch withhistory in the Attribute Editor on the avgCurve node created during thestitch (accessible through the Channel Box).

Note

The Stitch Tool does not change the number of CVs or the U/V spaceparametrization. It does modify the CV positions to get as close topositional and tangent continuity as possible.

Note

For illustrative purposes the following example displays in white. Mayadisplays this temporary stitch surface in bright green.

weight = 1.5 (default) weight = 0.5



You can drag the manipulators to selectively alter the portions along theisoparms to be weighted together. These are the portions on the two surfacesthat will be stitched together.

Setting the samples along the stitch edge

Samples AlongEdge

The CVs for the stitched surface are determined by sampling (discretizing)the edge along the surface which needs to be modified for C0, G1 continuity.You can explicitly set Samples Along Edge to close any possible C0 gaps onthe stitched surface. The higher the count, the slower the performance. Thisis the same as Step Count in the Channel Box and Attribute Editor.

Cascading the stitch node

Cascade StitchNodes

If Cascade Stitch Node is toggled on, the stitch operation ignores any priorstitch operations on the surface. If toggled off and the surface has had astitch operation performed on it, the stitch node from the previous operationis used. The default is on.

Keeping original geometry

If Keep Original is toggled on, the stitch surface is created on top of theoriginal input surfaces. This way, you can move the resulting surface if youare not satisfied with the result and restitch a new surface with differentoption settings.

If toggled off, the result of the stitch operation replaces the surface beingstitched. Keep Original is off by default.

Editing the stitched surface in the Channel BoxOnce you press Enter and then select the stitched surface, parameters for theinput surface and the resulting stitched surface are displayed in the ChannelBox. Click the heading for the stitch surface to display its parameters.

Tip

To see the curve computed by the average node, select the ShowManipulator Tool on the average node. This manipulator provides a visualclue only and cannot be edited.



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Continuity Type on or off in the Continuity boxes to toggle positional or tangentialcontinuity for the stitch surface.

Step Count Step Count means the same thing as Sample Count in the Surface Historysection of the options window. See “Setting the samples along the stitchedge” on page 334 for details.

Bias Use the Bias value to blend the CVs between the input surface to the stitchnode and the result from the stitch operation. A value of 0.0 has no effect.

Fix Boundary You can use the Fix Boundary option only if the Cascade Stitch Nodesoption and G1 continuity are on during the stitch operation. While solvingG1 continuity across all four edges, it is quite possible that the eight CVs(two boundary CVs next to each of the four surface corners, giving a total ofeight) could be modified; this may result in positional discontinuity. To avertthis, turn Fix Boundary on to ensure that the eight CVs remain unmodified.



Updating the stitch surface historyClick the Surface History tab to display the following parameters.

Blend Points Use the Blend Points toggles, Position Continuity and Tangent Continuity,to set local positional or tangential continuity on or off for surface points (ifyou are stitching the surface using edit points or CVs).

Blend Edge Use the Blend Edge toggles, Position and Tangent, to set local positional ortangential continuity on or off for surface edges.

Sample Count Use the Sample Count value to close any gaps between the surfaces. See“Setting the samples along the stitch edge” on page 334 for moreinformation.

Editing the stitched surface in the Attribute EditorTo edit the completed stitched surface, use the Attribute Editor. To open theAttribute Editor, either:




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The Stitch Surface History section gives you access to the input surface andthe curves that the stitch operation is attempting to stitch to. Click the arrowbuttons to select the surfaces or curves if you want to edit them.



Fix Boundary The Fix Boundary toggle is also available in the Channel Box. See “Editingthe stitched surface in the Channel Box” on page 334 for details.

Bias Use the Bias value to blend the CVs between the input surface to the stitchnode and the result from the stitch operation. A value of 0.0 has no effect.

Positional/TangentialContinuity

The Positional Continuity and Tangential Continuity toggles are alsoincluded in the Channel Box. Type on or off to globally set the continuity forthe surface edges. If toggled off (the default setting), the Step Count (orSampling Rate) is used as the tolerance value. If toggled on, you can set aspecific tolerance value.


Creating surfacesStitching surface points

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Stitching surface pointsUse Edit Surfaces → Stitch Surface Points to stitch NURBS surfacestogether by selecting points on the surface. Any type of surface point can beselected, including edit points, CVs, or surface points along the surfaceboundaries.

To stitch a surface using surface points:

1 Select the points on the surface you want to stitch together. In this example,edit points are selected from two primitive NURBS planes.

2 To select the edit points, click the Select by component type icon, click theParm Points icon and select Edit Points from the pop-up menu.

or

With the right mouse button over the active surfaces, select Edit Point fromthe marking menu.

3 Marquee-select the edit points you want to stitch together.

4 Select Edit Surfaces → Stitch Surface Points.



Setting Stitch Surface Points optionsSelect Edit Surfaces → Stitch Surface Points - ❐ to open the optionswindow.

Keeping original geometry

If Keep Original is toggled on, the stitch surface is created on top of theoriginal input surfaces. This lets you move the resulting surface if you arenot satisfied with the result. You can restitch a new surface with differentoption settings.

Assigning equal weights

Assign EqualWeights

If Assign Equal Weights is toggled on, a weighted average of the selectedpoints is performed both in position and normal using an averageNurbsSurfacePoint node.

If toggled on, all the points are assigned a weight of 0.5. When toggled off,the first selected point is assigned a weight of 1.0 and the rest of the points aweight of 0.0. The default is on.

Cascading the stitch node

Cascade StitchNode

If Cascade Stitch Node is toggled on, the stitch operation ignores any priorstitch operations on the surface. If toggled off and the surface has had astitch operation performed on it, the stitch node from the previous operationis used. The default is on.



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Editing stitched surface points in the Attribute EditorTo edit the completed stitched surface points, use the Attribute Editor. Toopen the Attribute Editor, either:





Input Surface The Input Surface box is read-only. You click the arrow beside its name toaccess the surface to edit it.

Fix Boundary/Bias

The Fix Boundary option and the Bias options are included in the ChannelBox for a stitched surface. See “Editing the stitched surface in the ChannelBox” on page 334 for details about these options.



Setting point constraint options

If you stitched edit points together, the Point Constraints options areavailable.

Parameter U / V Enter values in the Parameter U and Parameter V boxes to adjust the U or Vparameters of the edit points you used to stitch the surface.

Position /Normal

The Position and Normal information is read-only. These values indicate inwhich XYZ direction the edit points and surface normals are located.



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Setting the CV positions

If CVs are stitched together, the Override CV Position options are available.

CV Index boxes The CV Index boxes let you override the default (or initial) position of theCVs you used to stitch a surface together.

CV Position The CV Position information is read-only. These values indicate in whichXYZ direction the CVs are located.

To edit surface points in the Attribute Editor:

1 Click the NurbsSurfacePoints node heading in the Channel Box.

2 Click the option box (❐) next to its name in the Object pop-up menu.

Click this heading, then click the box besideits name in the Object pop-up menu.



To edit curve points in the Attribute Editor:

1 Click the avgCurves node heading in the Channel Box.

2 Click the option box (❐) next to its name in the Object pop-up menu.

Click this heading, then click the boxbeside its name in the Object pop-up menu



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For details about changing the weight factors for curves or isoparms, see“Determining the weighting factors for the input isoparms (edges)” on page333.


Creating surfacesCreating boundary surfaces

Creating boundary surfacesUse Surfaces → Boundary to create a three-sided or four-sided surface fromthree or four curves.

Creating a four-sided boundary surfaceBefore you begin, you need four boundary curves to define the profile of thesurface boundaries.

You can either marquee-select the four curves, or pick the curves in aspecific order. After you select the curves you want to use for the boundarysurfaces, select Surfaces → Boundary.

Marquee-selecting the curves

If you want to use this method, try to create the curves in the order that youwant the boundary surface to be constructed. Keep in mind that the firstcurve you create defines the U parameter of the resulting surface.

Picking the curves in a specific order

Although a specific order is not necessary when selecting the curves, it isrecommended that you pick the curves in opposing pair order. That is, thesecond curve you select should be the curve that is parallel to the first curveyou select. This lets you control which pair of curves will be modified andpositioned so their end points match with the end points of the second curvepair.

Keep in mind that the first selected curve defines the U parameter directionof the resulting surface.

1

2

3

4 U direction



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Creating a three-sided (triangular) boundary surfaceSelect three curves to define the profile of the surface boundaries, then selectSurfaces → Boundary.

Marquee-selecting the curves

If you want to use this method to select the curves, it is important to createthe curves in a specific order or the results may not be what you intended.Try to create the two curves that meet at the apex first, then create the thirdcurve. Notice the different results in the following illustration.

Picking the curves in a specific order

Although the direction of the three boundary curves is not important for atriangular boundary surface, the results can differ depending on the orderyou pick the curves. Remember that the first curve selected defines the Uparameter direction of the resulting surface and that the apex alwaysappears where the first curve meets the second curve.

These curveswere created first.

This curve wascreated first.

1

2

3U direction



In the following, the curves are selected so that the U direction is determinedby a different picking order.

Notes

A 3-sided surface is actually a 4-sided surface with one side that has zerolength. If the end points of two side curves are not exactly matched, then ashort straight line segment will result instead of a zero length line. The zerolength side occurs at the apex of the triangular surface.

The term degenerate surface is often used to describe a surface with a zeroedge length. Although degenerate surfaces are fine for visual purposes, theymay not be compatible with all manufacturing systems.

1

2

3

U direction



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Setting Boundary optionsSelect Surfaces → Boundary - ❐ to open the options window.

Determining the curve order

The Curve Ordering options affect the resulting surface depending on whatis set and how you select the curves.

Automatic/As Selected

Automatic is the default option setting. When As Selected is the curve ordersetting, the order in which you select the curves determines the resultingsurface.

In the following, the first surface is created by marquee-selecting the curveswhile Automatic is selected. The second surface is created when As Selectedis the option setting and you select the curves in a different order.



Setting common end points

Common EndPoints

The Common End Points options let you decide whether or not the endpoints should match before the boundary surface is created.

If you select Optional, the surface is created even if the end points don’tmatch (the ends of the curves don’t match). This is the default.

If you select Required, the boundary surface is only built if the end points ofthe curves match exactly. See the following three-sided boundary surface.

To make sure the end points match, remember to select a snap mode fromthe Status Line when drawing your curves.

If Automatic is selectedand you marquee-select the

1

2

3

4

If As Selected is selected,pick the curves in adifferent order to geta different result.

curves, you get this result.

Notice howthe curveend pointsare matched.



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To match the end points after you draw the curves:

1 Click to turn a snap mode on in the Status Line, such as Snap to grids.

2 While in component mode, select the edit point or CV you want to move.

3 Select the Move Tool and drag to snap the edit points or CVs to the sameposition.

Setting the end point tolerance

If you select Required as the Common End Point option, you can changethe End Point Tolerance value of the Local end points.

Tolerance Global tolerance means the Positional value you set in Options → GeneralPreferences → Modeling are used. Positional tolerance is used to determinehow close the end points need to be to be considered coincident. The defaultis Global.

Click to select a point, use the Move Tooland drag to snap the points together.

Click the Snap to grids icon.

Select a component mode.



Local tolerance displays the following where you can enter a new value tooverride the Positional tolerance value you set in Modeling Preferences.

Local tolerance is useful where you want to change these values often, butdon’t want to change the Global tolerance all the time.

Changing the curve point order and tolerance in the Channel Box

You can toggle the curve Order or End Point selection by typing on or off inthe boxes provided in the Channel Box. You can also set the tolerance of theend points by entering a value. These options are also available in theAttribute Editor.

Setting the curve range

Curve Range If you select Complete as the Curve Range, the boundary surface is builtalong the entire profile (or input) curve. This is the default.



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Editing part of a boundary surface

If the curve range is set to Partial in the options window, you can usemanipulators to edit the construction curves of the boundary surface.

1 Click the Show Manipulator icon and create the boundary surface.

2 Click one of the subCurve headings in the Channel Box to display themanipulators and edit the input curves.

Keep selecting subCurve headings to adjust the input curves as necessary.

Note

If Common End Points is set to Required, set the Curve Range toComplete.




OutputGeometry



Editing the boundary surface in the Attribute EditorTo edit the completed boundary surface, use the Attribute Editor. To openthe Attribute Editor, either:







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Input Curves The Attribute Editor for a boundary surface lists the read-only informationfor the input curves you used to build the surface. Click an arrow button toselect an input curve, then click the tab to open its section of the editor. IfPartial is the Curve Range in the options window when you create thesurface, information for the subCurves is also available.

The Order and End Point toggles, as well as the End Point Tolerance sliderare included in the options window and the Channel Box. See the optiondescriptions on page 349 for details.


Creating surfacesCreating birail surfaces

Creating birail surfacesUse the birail tools to create surfaces by combining three or four free-formcurves that intersect. Available tools include Birail 1 Tool, Birail 2 Tool, andBirail 3+Tool. The curves you select can be boundary curves of an existingsurface, isoparms, curves-on-surface, or trim boundaries.

If you know which options to set before you create the birail surface, openthe options window first, then use the tool to create the surface. Click theoption box (❐) after the tool name to change the option settings. See thefollowing for details about setting the options for each birail creationmethod:

• “Setting Birail 1 Tool options” on page 358

• “Setting Birail 2 Tool options” on page 365

• “Setting Birail 3+Tool options” on page 369

Alternately, you can create the birail surface with the default options andthen open the Attribute Editor to edit the completed surface. See thefollowing for details about the Attribute Editor for each birail creationmethod.

• “Editing the single birail in the Attribute Editor” on page 362

• “Editing the double birail in the Attribute Editor” on page 366

• “Editing the multi birail surface in the Attribute Editor” on page 370

Tip

To successfully build a birail surface, the input curves have to intersect therail curves. If you are building birail surfaces from curves, make sure theprofile curves cross the rail curves before you select the birail tools. Openall views to verify the intersection, or try using the front view.


Creating surfacesUsing the Birail 1 Tool

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Using the Birail 1 ToolUse the Surfaces → Birail 1 Tool to construct a surface by sweeping oneprofile curve along two rail curves. You can also construct the surface byreversing the selection order of the rail curves.

To build a birail surface from a single profile curve:

1 Select Surfaces → Birail 1 Tool.

2 Follow the prompts at the Help Line. Click the curve you want to use as theprofile curve, then click the two rail curves. The surface is displayed in theconstruction history color by default.

3 Press Enter to complete the birail surface.

Profile curve

Rail curves



Setting Birail 1 Tool optionsSet the tool options before you create the birail surface. To open the optionswindow, select Surfaces → Birail 1 Tool - ❐.

To change the options after the birail is created, use the Channel Box or theAttribute Editor. See “Editing the single birail in the Attribute Editor” onpage 362 for details.

Controlling the resulting transformation

TransformControl

As the profile curves are swept along the rails, you can scale themproportionally or non-proportionally while preserving the intersection withthe two rail curves. Select either NonProportional or Proportional.NonProportional is the default.



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To change the transformation from proportional to non-proportional:

Construct the rail curves in the XZ plane. Construct the profile curve so thatthe internal CVs are at some constant Y. By scaling non-proportionally, theinternal CVs of the birail surface also preserve the constant Y as the profile.

1 In the top view, create the two rail curves. Select Display → NURBSComponents → Edit Points to display the edit points on the curves.

2 Click the Snap to points icon on the Status Line, place the first point of theprofile curve, and click Snap to points again to turn snapping off.

3 In the front view, continue to place the points to create the profile curve.Select the Snap to points icon to snap the last point to the last rail curve(remember to turn snapping off afterward).



4 Build the birail surface, then while it is active, select a transform mode fromthe Channel Box. While the pointer is in the Transform Mode box, click withthe right mouse button to select a Transform Mode from the pop-up menu.

The following example shows what happens to the birail surface when youswitch between the transform modes.

Blending the profile curves

Edge Blending You can use the Edge Blending option, First Edge, only if the profile curveis a surface curve. If First Edge toggled on, the constructed surface is tangentcontinuous to the surface underlying the profile.

Non-proportional Proportional



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Rebuilding profile or rail curves

Toggle one of the Rebuild Options on to rebuild a profile curve or rail curvebefore it is used to create the surface.

Profile Curves Since only one profile curve is necessary when building a single birailsurface, First Edge is the only available Profile Curves rebuild option.

Rail Curves For Rail Curves, the First Edge option refers to the first input rail curve youselect when you build the surface. The Second Edge option refers to thesecond, or last, curve you select.

To display rebuild options and edit the profile and rail curves:

If you toggle one of the Rebuild Options on, rebuild nodes are insertedbetween the profile curve or rail curves and the birail surface creation node.This means the profile curve or rail curves can be selected from the ChannelBox and rebuilt using the parameters and options provided in the ChannelBox or in the Attribute Editor.

The following shows the Channel Box and Attribute Editor for a profilecurve when rebuild is toggled on.

To access the Attribute Editor for the selected curve:

• Click the option box (❐) beside Rebuild Curve from the History list menuon the Status Line.

• Click the option box (❐) beside Rebuild Curve from the Input pop-up menuin the marking menu.



See “Rebuilding curves” on page 199 for details about the options providedin this Attribute Editor.


OutputGeometry


Editing the single birail in the Attribute EditorTo edit the completed single profile birail surface, use the Attribute Editor.To open the Attribute Editor, either:





Transform Mode The Transform Mode options are included in the options window and theChannel Box.



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Input Profile /Input Rails

The Input Profile, and Input Rail 1 and Rail 2 information is read-only. Itgives you access to the input curves you used to build the birail surface.Click the arrow buttons to select the curves if you want to edit them.

TangentContinuityProfile

The Tangent Continuity Profile toggle lets you turn tangent continuity onor off for the input profile curve. You can use this to make the resultingsurface tangent continuous to the surface underlying the profile curve. Youcan also toggle this option on or off in the Channel Box in the TangentContinuity Profile box.

Note

For this toggle to take effect, the profile curve must be a curve-on-surface.



Using the Birail 2 ToolYou use the Surfaces → Birail 2 Tool to create a surface by blending twoprofile curves along two rail curves.

To build a birail surface from two profile curves:

1 Select Surfaces → Birail 2 Tool.

2 Follow the prompts at the Help Line. Click the curves you want to use as theprofile curves, then click the curves you want to use as the rail curves. Thesurface is displayed in the construction history color by default.

3 Press Enter to construct the double profile birail surface.



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Setting Birail 2 Tool optionsYou can set the tool options before you create the birail surface. To open theoptions window, select Surfaces → Birail 2 Tool - ❐.

To change the options after the birail is created, use the Channel Box or theAttribute Editor. See “Editing the double birail in the Attribute Editor” onpage 366 for details.

Most of these options are included in the Birail 1 Tool options window. See“Setting Birail 1 Tool options” on page 358 for details.

Since you need two profile curves to create a double profile birail surface, anextra Edge Blending toggle (Second Edge) and profile curve RebuildOption toggle (Last Edge) is included in this options window.

Surface Blend is the only option that is not included in the Birail 1 Tooloptions window.



Defining the surface blend

Surface Blend The Surface Blend factor value lets you alter the degree of influence theprofile curves have on the intermediate profiles of the created surface. Forexample, a value of 1.0 means the first selected profile curve has a greaterinfluence than the second profile curve. By default, both selected profileshave an equal influence value of 0.5.

You can also change the Surface Blend value in the Channel Box. While thebirail surface is active, click the heading to display the parameters and entera new value in the Blend Factor box.

Editing the double birail in the Attribute EditorTo edit the completed double profile birail surface, use the Attribute Editor.To open the Attribute Editor, either:





Click to display parameters.

Enter a new blend value here if necessary.



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The Transform Mode and Blend Factor options are included in the optionswindow and the Channel Box. See “Controlling the resultingtransformation” on page 358 for details about Transform Mode, and“Defining the surface blend” on page 366 about Blend Factor.

Input Profile /Input Rail

Because you use four curves to create a double-profile birail surface, theInput Profile and Input Rail information boxes list all of the curves youused as profile and rail curves. This gives you access to the input curves youused to build the birail surface. Click the arrow buttons to select the curves ifyou want to edit them.


The Tangent Continuity Profile toggles let you turn continuity on or off forthe input profile curves. Using this toggle, you can build a tangentcontinuous surface with the surfaces underlying the profile curves. You canalso toggle this option in the Channel Box by typing on or off in the TangentContinuity Profile boxes.

The Tangent Continuity Profile toggles are only valid provided the profilecurve is a surface curve (isoparm, trimmed edge, curve-on-surface).


Creating surfacesUsing the Birail 3+ Tool

Using the Birail 3+ ToolYou use the Surfaces → Birail 3+ Tool to create a surface by blendingmultiple profile curves along two rail curves.

To build a birail surface from multiple profile curves:

1 Select Surfaces → Birail 3+ Tool

2 Follow the prompts at the Help Line. Select three or more profile curves,then press Enter to confirm your choice.

3 Select the two rail curves. The surface is displayed in the constructionhistory color by default.

4 Press Enter to construct the birail surface.



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Setting Birail 3+Tool optionsYou can set the tool options before you create the birail surface. To open theoptions window, select Surfaces → Birail 3+ Tool - ❐.

To change the options after the birail is created, use the Channel Box or theAttribute Editor. See “Editing the multi birail surface in the Attribute Editor”on page 370 for details.

Most of these options are included in the Birail 1 Tool options window. See“Setting Birail 1 Tool options” on page 358 for details.

Since you need two profile curves to create a multi profile birail surface, anextra Edge Blending toggle (Second Edge) and profile curve RebuildOption toggle (Last Edge) is included in this options window.



Editing the multi birail surface in the Attribute EditorTo edit the completed multi profile birail surface, use the Attribute Editor.To open the Attribute Editor, either:





Input Profile /Input Rail

Because you use multiple curves to create a multi-profile birail surface, theInput Profile and Input Rail information boxes list all of the curves youused as profile and rail curves. This gives you access to these input curvesyou used to build the birail surface. Click the arrow buttons to select thecurves if you want to edit them.


The Tangent Continuity Profile toggles let you turn continuity on or offacross the first to last profile curve.



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You can also toggle this option in the Channel Box by typing on or off in theTangent Continuity Profile boxes.

You can also select a different Transform Mode (Proportional or Nonproportional) in the Channel Box.

While the birail surface is active, select a transform mode from the ChannelBox. While the pointer is in the Transform Mode box, click with the rightmouse button to select a Transform Mode from the pop-up menu.

See “Controlling the resulting transformation” on page 358 for details.

Note

For this toggle to take effect, the profile curves must be curves-on-surface.

Type on or off

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