14. Reverse Engineering

(Thanks to Yvan Germain and to Creaform for their contribution )

Reverse engineering is a relevant topic for this book, since with thedevelopment of recent data acquisition technologies, it allows more and moredesign and analysis possibilities.

This chapter does not intend to cover all software capabilities or workingmethodologies, but rather to give a quick overview of what can be done inthis eld. To do this, four dierent workbenches will be used: DigitizedShape Editor , Quick Surface Reconstruction, Free Style , and GenerativeShape Design , and it would be a good practice to have them readily availableby customizing the user environment and having the Workbenches toolbardisplayed on the screen to save time when moving from one workbench toanother.

DSE:Digitized Shape Editor

QSR:Quick Surface Reconstruction

FS:Free Style

GSD:Generative Shape Design

In all workbenches, tools will be available from toolbars or from the Insertpull-down menu. To facilitate the association of the tool with its respectiveworkbench, each workbench acronym (DSE , QSR, FS, or GSD ) will beincluded within parentheses in the command name.

Reverse Engineering

In order to illustrate some commands or behaviors, an STL le is used as ascanned support. This cloud of points le could come from a laser scanner orfrom another source.

This chapter will cover the following:

Importing/exporting a cloud of points

Aligning the scanned model

Generating geometry from the cloud of points

14.1. Importing/Exporting a Cloud of Points

The rst thing to do when working with a cloud of points is to import it into apart. Since the data le cannot be opened directly in CATIA , it is necessaryto launch a new part and to activate the Digital Shape Editor workbench inorder to be able to access related tools. Note that a cloud of points can alsobe imported into a product if needed.

CLOUD IMPORT TOOLBAR (DSE)

Import (DSE)

As shown in Figure 14-1, the Import tool brings up a dialog box that allowsthe user to select the le containing the point data and to format it in orderto get the desired working elements in the 3-D environment.

Info: Imports a cloud lePrompt to User: Select a format and a le to preview or import

To start, it is necessary to select the scan Format to get the right leextension from the list of available formats; here, STL will be used. The le toopen then has to be loaded. This can be done by clicking the ellipsis ()button and browsing the available folders. After this, the Scale Factor mustbe checked in order to reect scan le units and system units; for example, ifa scan was done using mm as reference units and is loaded on a system thatuses inches as working units, it will be necessary to use a 1/25.4 factor inorder to have the le read at the proper scale. Finally, clicking the CreateFacets check box will generate a mesh of triangular facets that will be usefulfor some operations. Clicking Apply will allow previewing the result, whileclicking OK will conrm and end the operation. The entire scanned lecontent will then appear on the screen, as shown in Figure 14-2.

Figure 14-1. Import dialog box.

Export (DSE)

Exporting a cloud of points is sometimes necessary in order to decrease theamount of data to work with or to create partial data les. In the Export tooldialog box, shown in Figure 14-3, the user is allowed to choose theElement(s) to export and browse in order to locate the folder in which the lewill be saved. Clicking the OK button will complete the operation. It isimportant to note that the data will be exported using the system's units andwill not necessarily keep the original units used.

Figure 14-2. Imported scan.

Info: Exports a cloud to a lePrompt to User: Select visible clouds or meshes to export

14.2. Aligning the Scanned Model

A model that is scanned is not always properly oriented or positioned withrespect to the coordinate system when it is inserted into a .CATPart le. Ifsome scan post-processing is necessary, it is good to know how to manipulatea cloud of points in the 3-D environment since it can be required for furtheroperations later on. This is done by creating reference elements from areasor features of the cloud of points and using them to locate the entire cloudwith respect to these references.

CLOUD EDITION TOOLBAR (DSE)

In many cases, a cloud of points will need to be broken in smaller point setsin order to be manipulated or reworked. This will usually not be done bydeleting elements from the set, but by activating or deactivating theelements that are necessary to perform a certain task.

Activate (DSE/QSR)

Figure 14-3. Export dialog box.

Info: Activates or deactivates cloud areasPrompts to User:When the tool is activated : Select the cloud of points or the mesh toprocessWhen a cloud is selected : Message varies with selected mode

The Activate tool allows the user to select only scanned elements he or shewants to work with. The displayed dialog box, shown in Figure 14-4, allowsthe user to select among dierent options to make the element selection. TheBrush option, used in the illustration to prepare elements in order to createa planar reference, selects a number of elements with a single stroke and isvery ecient to use. Note that if too many elements are selected, it ispossible to deselect some of them by pressing the SHIFT button while movingthe cursor. If the Trap option is used, there is a possibility that elementslocated at a distance from the area of interest are selected at the same time.The Flood option then allows the user to select the ones that are connectedtogether. By clicking the OK button, only the selected elements will stayvisible on the screen, with the others being deactivated. To retrieve thecomplete cloud denition, it is necessary to reuse the tool, to select the cloudof points in the 3-D environment or in the Part Specication Tree , and to usethe Activate All button.

Figure 14-4. Activate dialog box.

Remove (DSE)

As mentioned previously, while selecting elements to activate them, it ispossible to use the SHIFT button to deselect some elements. The Remove toolpermanently removes elements from the cloud of points kept in the le andthen creates a hole in the mesh, as shown in Figure 14-5. Elements removedcannot be recovered. If a removed element needs to be used again, theoriginal cloud of points must be imported again.

The tool oers a dialog box similar to the one used by the Activate command,as shown in Figure 14-6.

Info: Removes points/vertices/trianglesPrompts to User:When the tool is activated : Select the cloud of points or the mesh toprocessWhen a cloud is selected : Message varies with selected mode

Figure 14-5. Removed points from scan.

SURFACE CREATION TOOLBAR (QSR)

In order to be able to realign the cloud of points with respect to the partcoordinate system, it is necessary to create reference elements to performthis task.

Basic Surface Recognition (QSR)

The Basic Surface Recognition tool oers predened primitive-like options tocreate surfaces from an activated portion of the cloud of points. When usingthe Plane option, the green arrows appearing on the surface boundaries can

Figure 14-6. Remove dialog box.

Info: Recognizes Basic SurfacePrompt to User: Select a cloud to be analyzed or a line to set the directionof the axis or a point to set the center

be used to resize the planar element you want to create, while the greencircle surrounding the surface can be used to rotate it in the 3-D space, asshown in Figure 14-7.

When creating a surface using this tool, it is important to click the Morebutton in order to get information about the quality of the surface objectcreated, as shown in Figure 14-8, when using the Cylinder option. Mean andmax errors can then be known.

Figure 14-7. Basic Surface Recognition dialog box.

When creating reference elements, it is important to create a geometry thatwill not lead to a mismatch of the cloud of points with its former set ofreferences. For example, in the proposed model, the hole in the propeller wasobviously created centered to it and normal to its forward face. By creating acylindrical surface from points taken on the face of the hole, there is apossibility that the Cylinder 's axis is shifted from center and not normal tothe forward face of the propeller, as shown in Figure 14-9.

Instead of using this approach, which could lead to errors, it is a betterpractice to dene the center and the axis of the propeller by taking anapproach using the initial reference planar face created to extract a sectionand get the center location from it. To create the section in the proposedmodel, it will be necessary to reactivate the entire cloud. In someapplications, activating a portion of the cloud could be enough.

SCAN CREATION TOOLBAR (QSR)

Planar Sections (QSR)

Figure 14-8. Surface recognition of a cylinder.

Figure 14-9. Geometrical mismatch.

Info: Cuts a cloud of points into planar sectionsPrompts to User:

The Planar Sections tool allows the dynamic creation of one or many sectionsin the cloud of points with respect to a planar reference, as shown in Figure14-10. It creates objects in the model that can be post-treated but that cannotbe exported as geometry. When launching the command, it is necessary toselect the cloud of points to consider and a planar reference to dene thesection. By using the green arrows displayed on the plane icon appearing onthe cloud of points, it is possible to dynamically locate the level of thesection. By populating the corresponding edition boxes of the dialog box, it ispossible to generate a series of equidistant sections. To complete sectioncreation, it is necessary to click the Apply and then the OK buttons.

When the tool is activated : Select the element to treatWhen the scan is selected : Select a plane or modify specications orpress OK, Apply or Cancel

Figure 14-10. Using planar sections.

A created section may contain more data than is needed. It is then possibleto use the Activate tool on sections in order to keep only what is necessary toperform the desired operation.

The inner portion of a planar section can easily be ltered by using theInside Trap option of the Activate tool, as shown in Figure 14-11. To denesuch a ltered section, it is possible to choose the Polygonal Trap Type to goaround the geometry of interest. A Trap is completed by double-clicking thelast point. The selected portion of the section will then be used to retrievethe hole size and center location.

CURVE CREATION TOOLBAR (QSR)

Sketch From Scan (QSR)

Figure 14-11. Planar section partial activation.

Info: Creates sketch from a scan or a set of scansPrompts to User:When the tool is activated : Select a scan or a meshWhen the scan is selected : Modify specications or press OK, Apply orCancel

The Sketch From Scan tool allows the user to create a primitive-like sketchfrom a Planar Section element. By using the Primitive option found in thedialog box, it becomes possible for the user to right-click the Automatic gripthat appears near the geometry and then select a planar shape from acontext menu. A Tolerance can be entered prior to clicking the Apply buttonto have the selected element calculated and located in a sketch, and clickingthe More button will show information about the quality of the proposedgeometric element, as shown in Figure 14-12. The created sketch can be usedas is or be edited in order to add a center point as an Output Feature forfurther use.

When elements are created from the cloud of points, wireframe referenceelements can be created on it to facilitate the alignment procedure. Theelements can be created by using any wireframe tool. These tools can beretrieved from the DSE , QSR , FS, or GSD workbenches.

WIREFRAME TOOLBAR

(DSE/QSR/FS)

(GSD)

The goal is to add wireframe elements that will be used to locate the cloud of

Figure 14-12. Sketch from Scan dialog box.

points at the origin of the part. Any tool option can be used as long as itallows creating the desired reference geometry, such as for a Plane element ,Parallel through point , Oset from Plane , etc. All created elements appearin the active GeoSet in the Part Specication Tree , as shown in Figure 14-13.

After the necessary elements are created through the cloud of points, it maybe necessary to create some more elements at the origin (or at the locationwhere the cloud of points is desired). With all reference elements created, itthen becomes possible to have the cloud of points located at the origin.

CLOUD REPOSIT TOOLBAR (DSE)

Align With Constraints (DSE)

Figure 14-13. Wireframe geometry added.

Info: Aligns clouds with a selection of constraintsPrompts to User:When the tool is activated : Select the cloud to alignWhen the cloud is selected : Use Add to add a constraint then Apply toupdateWhen the Add button is clicked : Select a rst constraint element in thecloud to alignWhen an element is selected in the cloud : Select a second constraintelement in the referenceWhen an element is selected in the reference : Use Add to add aconstraint then Apply to update

A very eective way to have the cloud located at the origin is to use the Alignwith Constraints tool. It basically works by adding constraints betweenelements the same way as when adding constraints in an assembly, excepttraces of the elements selected to make the alignment are available in thedialog box, as shown in Figure 14-14.

Using the tool does not move the original cloud of points. Rather, it creates anew version of the cloud properly located, as shown in Figure 14-15. Theoriginal version of the cloud of points, as well as the Axis Systems created bythe operation, can then be deleted if desired.

14.3. Generating Geometry from the Cloud of Points

Figure 14-14. Aligned with Constraints dialog box after using Apply.

Figure 14-15. New aligned cloud created.

With the cloud of points properly located at the desired location, it is usuallyeasier to start to rework the geometry since part reference planes becomeavailable as work references.

If the shape is organic (no prismatic shape), no rough material part can reallybe created. In this case, surfaces will be created from portions of the cloud ofpoints, and the nished model will become a patchwork of a series ofsurfaces extracted, reworked, and blended. However, if a rough solid can bemade, like in the presented model shown in Figure 14-16, it may be shapedwith surfaces created from the cloud of points. This is the beginning of aniterative process where surfaces will be best tted, trimmed, lleted,untrimmed, etc.

The following lines will just give an idea of the work that has to be done inorder to rework an entire cloud of points. Since many of the operationsinvolve GSD workbench's tools already covered previously, they will just bepointed out in the text. Refer to Chapter 9 for more information.

To start, a visual analysis of the cloud of points will allow the user to identifyzones to consider in order to best t surfaces, as shown in Figure 14-17. Thedesired zone can then be activated.

Figure 14-16. Rough solid.

SURFACE CREATION TOOLBAR (QSR)

Power Fit (QSR)

The Power Fit tool allows the user to best t a surface from a selected groupof points. When activating the tool, it is necessary to rst select the cloud ofpoints. The Activate tool icon, found in the Preparation tab of the dialog box,as shown in Figure 14-18a, must then be clicked in order to use the desiredcommand options to dene the points to work with. If a certain region isalready activated prior to launching Power Fit , it is still necessary to use theActivate tool; however, in that case, the Brush option is the best to use tomake a quick selection.

Figure 14-17. Zone to consider.

Info: Power tPrompt to User: Select a Cloud or Curves

Once the region is selected, it is necessary to select the Parameters tab tocreate the settings relative to the surface that will be dened. Depending onthe quality you want to achieve for the nished surface model, Tolerance ,Order , and Segment parameters will be dened, as shown in Figure 14-18b.When the settings are complete, it is necessary to click the Apply button inorder to make the new surface appear.

Finally, it is a good practice to have a look at the Information tab, shown inFigure 14-18c, to get data about the accuracy of the surface created from theselected cloud of points region. Depending on the tolerance that can be

Figure 14-18. Power Fit Tool dialog box.

allowed, the surface element will be accepted or rejected. The OK button canthen be clicked to complete the creation of the surface.

In order to verify the quality of a surface with respect to a cloud of points, anumber of tools are available at any time to the user. One of the most usedcompares variations with points and a given surface.

CLOUD ANALYSIS TOOLBAR (QSR)

Deviation Analysis (QSR)

The Deviation Analysis tool is used to graphically quantify the deviation of asurface with respect to a cloud of points. In order to use it, however, it is rstnecessary to set the shading mode to Shading with Material .

As shown in Figure 14-19, the cursor can be moved over the surface to get alocal deviation of the surface while in the analysis process. The graphicresult of the analysis is stored in the Part Specication Tree and can behidden, but it can be reactivated and made visible with a double-click.

Info: Analyzes deviations between datasPrompts to User:When the tool is activated : Select the reference dataWhen the cloud of points is selected : Select the data to measureWhen the surface to compare is selected : Modify specications or pressOK, Apply or Cancel

From here on, the surface denition process becomes highly iterative.Depending on the shape you want to rework, you might have to use thePower Fit tool to create surface patches, to create curves on the patches inorder to use the curves to trim the surfaces to a certain dimension, to createmigration surfaces between the patches created on the cloud, to undo. etc.

The following sections describe the tools used in dierent situations toperform these tasks.

OPERATION TOOLBAR (QSR)

OPERATION TOOLBAR (GSD)

Extrapolate (QSR/GSD)

Figure 14-19. Deviation Analysis dialog box.

Info: Creates a surface or curve by extrapolationPrompts to User:When the tool is activated : Select a boundary (a point or a curve)When the endpoint of a curve or the edge of a surface is selected :Select the curve or surface to extrapolateWhen the object to extrapolate is selected : Modify specications or pressOK, Apply or Cancel

The Extrapolate tool creates a new curve or surface from another one byextrapolating it along one of its limits. The created object is added in thePart Specication Tree , while the reference one is hidden in No Show . Anumber of parameters can be modied in the dialog box displayed to theuser, as shown in Figure 14-20. The created geometry, if ever disassembled,will break up in two dierent elements: the reference element and theextrapolated portion.

SHAPE MODIFICATION TOOLBAR (FS)

Extend (FS)

The Extend tool allows the user to change the dimensions of the selectedcurve or surface by modifying its denition parameters, which has theadvantage of keeping a single geometry element. When the element isselected, green square grips appear at its limits. Selecting and dragging anyof these grips will allow the user to modify the geometry. As shown in Figure14-21, the associated dialog box is kept minimal.

Figure 14-20. Extrapolate dialog box.

Info: Extends curves or surfaces of a given lengthPrompt to User: Select a curve or a surface

CURVE CREATION TOOLBARS

(DSE)

(QSR)

(FS)

3D Curve (DSE/QSR/FS)

The 3D Curve tool allows the user to create a spatial curve through a seriesof point selections. The last point of the curve must be double-clicked. Thecreated curve will pass by the points, but will not necessarily be done on asurface, unless it is planar. A number of options can be set in the associateddialog box, as shown in Figure 14-22.

Figure 14-21. Extend dialog box.

Info: Creates 3D curves by clicking points either in space or on existinggeometry (points, clouds, curves, surfaces)Prompts to User:When the tool is activated : Click anywhere to create your constructionpoints. Scans of points can also be selectedWhen a point is created : Click anywhere to create your constructionpoints. Scans of points can also be selected

Curve on Mesh (DSE/QSR)

The Curve on Mesh tool allows the user to create a spatial curve through aseries of point selections made from the scanned points. The last point of thecurve must be double-clicked. Parameters of the created curve can be set inthe associated dialog box, as shown in Figure 14-23.

Figure 14-22. 3D Curve dialog box.

Info: Creates 3-D curves on mesh.Prompts to User:When the tool is activated : Select a meshWhen a mesh is created : Pick on the support mesh to create split orinternal points or move the pointer over control points to make onlineedition, or press the 'Shift' key to modify the current constraint type

Curve on Surface (FS)

The Curve on Surface tool allows the user to create a curve that lies on theselected surface by a series of clicked points, with the Point by Point type,or to get a dynamic isoparameter creation using the Isoparameter type. ThePoint by Point type creation uses a spline-type curve from a series of controlpoints joined by a control polygon, as shown in Figure 14-24. The last point ofthe curve must be double-clicked.

Figure 14-23. Curve On Mesh dialog box.

Info: Creates a curve on a surfacePrompts to User:When the tool is activated : Select a faceWhen a face is created : Click the current isoparametric or the currentpoint

Isoparametric Curve (FS)

The Isoparametric Curve tool allows the user to create a curve on the surfaceby rst clicking a point on the desired surface, which causes anisoparametric curve with a large red dot to appear, as shown in Figure 14-25. This curve can be moved in any direction of the surface. By clicking apoint at any given location, a new green grip appears to relocate the curve ifnecessary.

Figure 14-24. Curve On Surface dialog box.

Info: Creates isoparametric curves on a supportPrompts to User:When the tool is activated : Select surface on which Isoparametric curve tobe createdWhen a face is created : Click on the selected surface to create Isocurve orselect Point selector to select/stack PointWhen a point is clicked : Select Cells for Swapping the Isoparam CurveDirection on those cells on which Isoparam curve is created

SURFACE OPERATION/CREATION TOOLBARS

SPLIT/TRIM TOOLBAR (QSR)

TRIM-SPLIT TOOLBAR (GSD)

OPERATIONS TOOLBAR (GSD)

SURFACES TOOLBAR (GSD)

SURFACES TOOLBAR (FS)

A number of surface modeling tools can be used to rework or create surfacesin order to get a series of patches that will closely recreate the envelope ofthe cloud of points and that will be used to create or shape a solid object. Inmany cases, a surface patch created by an operation will have to be cut orextended in order to be better dened for the following operation.

Working meticulously will allow the user to generate an excellent result fromthe scanned geometry, as shown in Figure 14-26.

Figure 14-25. Isoparametric Curve dialog box.

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This chapter covered a number of tools allowing the user to work with cloudsof points generated for inspection or reverse engineering purposes. Good-quality models ask for time, experience, and patience.

Figure 14-26. Completed work.

Citation

Michel Michaud: CATIA Core Tools: Computer Aided Three-Dimensional InteractiveApplication. Reverse Engineering, Chapter (McGraw-Hill Professional, 2012),AccessEngineering

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