Fit Curve

What is it?

Use the Fit Curves command to create a quadric curve or a spline by fitting it to specified data points.

Example of fitting a spline on a facet body

You can fit splines, lines, circles, and ellipses.

Splines, circles and ellipses, can be open or closed.

Lines and open circles, splines, and ellipses can be extended using on-screen handles or input boxes.

The maximum fitting error and the location of the error is displayed on-screen.

The data points can reside in a set of chained points, or on facet bodies, curves, or faces.

For splines, you can set endpoint and inner continuity constraints, and you can control the accuracy and shape of the fit by specifying:

Degrees and Segments

Degree and Tolerance

Template Curve

An associative Fit Curve feature is created when curves, faces, chained points, or selected points are the target. Any modifications to the target object causes the associated fit curve to update accordingly. Curves fitted to facet bodies have no associativity.

Why should I use it?

Fitting curves as cross sections, to either scanned point cloud data or facet bodies, creates the necessary guide and section curves to begin surfacing, which is a fundamental part of Reverse Engineering workflows.

Where do I find it?

Application Modeling, Shape Studio

Toolbar

Curve→Fit Curve

Shape Studio→Curve Drop-down→Fit

Curve

Menu Insert→Curve→Fit Curve

Fit Curve dialog box

Type

Determines the type of geometry to fit to specified data points.

Data points can be from various sources, such as specified points, chained points, point sets, and points on curves, faces, and facet bodies.

The dialog box groups and options change depending on the type selected.

Fit Spline

Lets you:

Use curves, faces and facet bodies as a target source.

Specify point constraints and start and end point tangency. Right click spline points for on-screen constraint options.

Specify a projection direction if the points you are specifying are not directly on the target.

Control parameterization such as degree, number of segments, and tolerance. You can fit a closed spline and make all segments uniform.

Extend the start and end of the fitted spline either individually or symmetrically.

Fit Line

Fit Circle

Fit Ellipse

Lets you:

Infer points, select or specify points or use a chain of points as the target source.

Extend the start and end of the fitted curve, either individually or symmetrically.

Fit a circle or ellipse as open or closed geometry.

Target

Source list

Infer

Automatically infers the source type from the geometry you select based on the following rules:

If you select points using lasso or rectangle selection, the source type is Specified Points.

If you select a single point the source type is Chained Points and you are prompted to select an end point.

If you select a point set or point group, this has selection priority before the individual point of the set or group. The source type is Specified Points.

Use QuickPick to select a single member point.

If the user selects a curve the source type is Curve

If the user selects a face the source type is Face

If the user selects a facet body the source type is Facet Body.

Point snapping is not available when Source is Infer mode to support chaining.

Use the selection filter of Curve Feature to filter for point sets when using Infer.

Specified Points

The Point Constructor is available to create target points when target points do not

already exist.

Use the selection filter of Curve Feature to filter for point sets when using Specified Points.

Chained Points

When the start and end points are specified, all the points in between are selected.

The All Points in Part check box is available. When selected, all the points are used for the fit.

Curve

Fits a spline to the selected curve. Parameterization options determine the closeness of the fit.

Face

Fits a spline to specified locations on a selected face using the Constraint Manager.

Facet Body

Fits a spline to specified locations on a selected facet body using the Constraint Manager.

Edit Fit Points

Available when Source is Infer, Specified Points or Chained Points.

Lets you select fit points and dynamically edit their locations. Maximum Error is displayed graphically and in the dialog box.

Average Error is displayed only in the dialog box.

Point Constraints

Available when Type is set to Fit Spline.

If the target sources are points, constraints are limited to the start and end of the spline. If the target source is a face or facet body, you can insert any number of internal constraints.

 

Edit Constraints

End Constraints

Start / End

Specifies which end point constraint is edited.

  Specify Tangent

Vector options and the Vector dialog box are available to specify a vector for the tangent direction of the end point.

Reverse Direction

Lets you reverse the specified vector.

Fit Conditions

Available when Type is set to Fit Circle or Fit Ellipse.

Radius Fits a circle to the target with a specified radius value.

Closed Fits a closed circle or closed ellipse to the target.

When selected, the Extension group is not available in the dialog box.

Projection

Available when Type is set to Fit Spline and Source is set to Infer, Face or Facet Body.

Determines the direction of projection of specified points onto faces, facet bodies, and in inferred selection.

XC YC ZC

Normal

View

Vector

ParameterizationAvailable when Type is set to Fit Spline.

Method list

Degree and Segments

Fits the spline to the target as closely as possible using Degree and Segment values provided.

Degree and Tolerance

Fits the spline to the target as closely as possible using Degree and Tolerance values provided.

A spline is fitted to the specified degree, using as many nonuniform segments as necessary to reach the tolerance.

A warning is displayed if the fitting operation cannot achieve the tolerance.

Any applied start and end constraints are not violated in order to meet the tolerance target.

Template Curve

Fits the spline to the target using the degrees and parameterization of an existing curve.

Degree Specifies the degree of the fitting spline.

Segments Available when Fitting Parameters is set to Degree and Segments .

Specifies the number of segments of the fitting spline.

ToleranceAvailable when Fitting Parameters is set to Degree and Tolerance .

Specifies a distance tolerance.

The default Tolerance value is set in Modeling Preferences.Closed Fits a periodic spline to the target.Uniform Segments

Specifies segments of equal arc length for the fitted spline.

Select Template Curve

Specifies a template curve that defines the degrees and segments of the fitted spline.

This option is automatically activated when you choose the Template Curve fitting parameter.

A spline is fitted to the target as closely as possible using the degree and parameterization of the selected template curve.

Keep Template Curve Selected

Keeps the template curve selected after pressing Apply.

Use this option when you want to create a set of curves with the same parameterization for input to a loft operation.

ResultsResults information is updated in the dialog box as geometry is manipulated on-screen.

Results depend on the Type specified.

Number of Poles – spline

Number of Segments – spline

Radius – circle

Major Radius – ellipse

Minor Radius – ellipse

Maximum ErrorDisplays the maximum deviation from the target to the fitted curve.

This information is also displayed on-screen.Average Error Displays the average deviation from the target to the fitted curve.ExtensionThe Extension options are available for Fit Circle and Fit Ellipse only when they are open circles and ellipses.

Symmetric

Develops a symmetric extension on both the specified start and end of the selected curve. The extension can be positive or negative.

Open fitted ellipse with 20 mm positive extension

Start /End

Available when the Symmetric check box is not selected.

None – Does not create an extension.

By Value – Specifies a value for the extension.

By Point– Defines a location for the extent of an extension.

SettingsAssociative Makes the fitted curve associative and parametrically related to parent features.

An associative fitted curve creates a Fit Curve feature.

Associativity is determined by the type of target and how points are specified. The following rules apply.

Inferred constraints of curve points have associativity.

o If the parent is modified the curve feature updates.

o If the parent is deleted after creation of the fit curve feature, it does not change its shape, and loses its associativity.

Specified Points do not have any associativity. They are stored as simple coordinates.

Note If the Point Constructor is used to select a point on an object such as a curve endpoint, then the point is associative.

Selected points have associativity. If a parent point is moved, the fit curve updates.

Selected Point Sets or Groups are always handled as selected points with the according associativity.

Chained Points have associativity. If a parent point is moved after creation of the feature, the fit curve feature updates.

Warning

If you use the constraint manager to move a point, that point loses associativity and becomes a specified point.

Points from any source which have been moved and snapped to an object are associative to this object.

A Curve target has associativity. If the target curve is modified the fit curve feature updates accordingly.

A Face target has associativity. If the target face is modified the fit curve feature is re-projected to the target and updated accordingly.

A Facet Body target has no associativity. Modifying the target does not update the fitted curve.

Automatic Point Rejection

Specifies a Rejection Threshold distance.

Points lying outside the threshold are not be taken into consideration for the fit operation.