Catia_Best_Practices

UG/Catia Data Exchange Best Practices

Unigraphics Solutions

Revision 3November 2, 1999

Version Modifier Date Description

1.0 Joe Lackner January 26, 1998 Initial Release

2.0 Joe Lackner April 21, 1998 Added MODEL_DIMENSION description

3.0 Joe Lackner November 2, 1999 Updated Text, added best practices for file size, what to look for when volumes don’t match, and tips on symmetric/mirrored data


Introduction............................................................................................................................. 1

Rule 1: Decide what needs to be exchanged..........................................................................2

Rule 2: Process for better exchange......................................................................................2

UG to CATIA Process........................................................................................................... 4

Rule 3: Prepare / Organize Data Before Translation...........................................................4Model Preparation Best Practices.....................................................................................4Creation of UG Verification Check Data..........................................................................5Cloud Of Points............................................................................................................... 5Volume, CG, and Surface Area........................................................................................5Translate the Data............................................................................................................6Theorem Direct UG to Catia............................................................................................6UG to STEP and STEP to Catia.......................................................................................7IGES............................................................................................................................... 8Check Fatal Errors......................................................................................................... 10Alternate Methods.........................................................................................................10Generate UG Validation Data........................................................................................10

Catia to UG Process............................................................................................................. 12Prepare / Organize Data for Translation.................................................................................12

FILTERING.................................................................................................................. 12PART MERGE.............................................................................................................. 13CATMOD...................................................................................................................... 13CATCLN....................................................................................................................... 13Model Preparation Best Practices...................................................................................14Data Validation Errors...................................................................................................15Creation of CATIA Verification Check Data.................................................................15Cloud of Points.............................................................................................................. 15Volume, CG, and Surface area.......................................................................................15

Translate model..................................................................................................................... 16Theorem Direct Catia to UG..........................................................................................16Catia to STEP and STEP to UG.....................................................................................17IGES.............................................................................................................................. 18Check Fatal Errors......................................................................................................... 18

Alternate Methods................................................................................................................. 18

Appendix A.......................................................................................................................... 19Simple Graphics Data....................................................................................................19Facets............................................................................................................................ 19Geometry....................................................................................................................... 19Boundary Representation Topology...............................................................................20Drafting Annotations & Symbols...................................................................................20Data Organization.......................................................................................................... 20Associative Relationships..............................................................................................21Feature and Parameter Data...........................................................................................21

Appendix B.......................................................................................................................... 22Tools 22Product Descriptions.............................................................................................................. 23

IGES.............................................................................................................................. 23STEP............................................................................................................................. 23VDA FS......................................................................................................................... 23Theorem Direct.............................................................................................................. 24

Appendix C.......................................................................................................................... 25

Common Catia Terms and Rules for the Unigraphics User...............................................25



Data Interoperability Strategies Page 1

Introduction

Exchange of data between Unigraphics and Catia is one of the most common exchange pairs in the CAD/CAM industry

Making the exchange successful between both systems seems like black magic among the newly indoctrinated to the ways of data exchange, but does not need to be. Knowing some of the basic questions to ask and gaining some understanding on what to expect will improve the users success and comfort level with moving data between the two systems.

This document outlines rules, processes, and tips to follow which should help those users who need to get data between the two systems.



Rule 1: Decide what needs to be exchangedThe first step of exchange is deciding what needs to be exchanged and then choosing the appropriate tool to do the job. It is important to focus on the pieces of data required to accomplish the tasks on the receiving end. Often the default is to send everything from A to B, when only a small amount of the data is actually used on the other side. Limiting exchanges to the required data significantly improves the success of exchange and reduces confusion. Construction and reference geometry that does not add any value can be eliminated. If the end goal is to support a Digital Pre Assembly process the data requirements may be different than if supporting machining operations etc.. Data that modern CAD systems create fall into roughly the following categories. Simple graphics data, Facet data, Geometry Boundary representation topology, Drafting annotations and symbols, Data organization, Associative relationships, Feature and parameter data. See Appendix A for more details on each of the types. See Appendix B for a data type versus tools pairing.

Rule 2: Process for better exchange

Defining the process for exchange is an important step to making data exchange work. The process should take into consideration not only the steps to do the exchange, but should be extended to include the appropriate steps to be taken in design. The steps for any sites' individual exchange needs might include: data management to organize data on specific layers to segregate construction geometry from actual part geometry; design validation before exchange; cleanup of parts for exchange; and rework if necessary. The documented process presented here focuses on the steps from the time data is ready for exchange.





UG to CATIA Process

Rule 3: Prepare / Organize Data Before TranslationThe exchange from UG to Catia starts with the part file. Understanding that the receiving system does not support geometry, data management, assemblies in the exact same manner and preparing for that fact will improve your ability to move the data. Segregating geometry on the appropriate layers and building the translation process to move only those layers is a good first step. Understanding how assemblies, layers, etc. are handled on the receiving end, and adjusting your data management to take into account the data’s destination will help achieve better exchange. Making sure that the geometry is clean will also be critical in having a good exchange.

Model Preparation Best PracticesTip: File size

One of the problems seen most often in the exchange of assembly files from UG is the creation of a Catia model file that exceeds the size limit on the receiving end. These limits vary from site to site, so check with the people with whom you are exchanging to see what their limits are. Limits at some sites for Catia models have been as small as 2 Mb. The size limit can occur because the assembly structure, as stored in UG with components as individual parts, will result in single model file in Catia containing details and dittos which exceeds the site limit. This can even happen when assemblies are not involved where an individual component can cause the size limit to be exceeded because of the nature of the model. To remedy this problem the UG part assembly may have broken down into smaller subassemblies or in rare cases the solid may have to be broken into smaller pieces. Also check the part for duplicate data and eliminate any duplicate surfaces, solids, curves etc.

File size can also be impacted by tolerance settings available in each of the translators. See notes on the specific translator settings for these values.

Tip: Translate only the necessary geometry

Organize data so only necessary geometry is translated. There are many ways to accomplish this in UG. If the user wants the translator to do most of the work, segregate construction geometry from exchange geometry by layer. Most translators support this. The user interfaces usually allow layers to be turned off from processing.

Tip: Bad data doesn’t get better with translation

Run Info->Analysis->Examine Geometry on all geometry before converting. Remove all tiny faces and tiny edges; fix self intersections, face inconsistencies and check for any other critical errors. Tiny geometry can cause failures in translation on the receiving end of a Unigraphics data. The data may be perfectly valid in Unigraphics but may not be intended by the designer.

Creation of UG Verification Check Data



UG check data can be used at several points throughout the process. First, it is used to validate that the model preparation process has not modified the CATIA geometry. Second, it will be used to validate the geometry once it is in Catia. The data acceptance standard may vary by site. The values below are an example.

Cloud Of Points

A cloud of points are projected to the critical areas of the part, including the following: Mating areas Specific blended surfaces Pockets

The point data can be created interactively in UG by using the point sub function.

In CATIA, the maximum deviation tolerance will be .0039 in or .1 mm. If points fall out of this tolerance range, recheck that the points were created correctly. For example, a problem might be creating points on SolidMs geometry before it was converted to SolidE and then STEPed out (although, procedurally, this should never be done).

Volume, CG, and Surface AreaThe volume of a closed body is a good high-level indicator if the part has changed through translation. The volume, CG, and surface area can be obtained by Using the Info->Analysis->Mass Properties Using Solids. The information can be placed in a text file using the print option. The criterion for CATIA-UG allowable deviation for the volume or surface area metric is .1% of the original volume or surface area. For CG .0039in or .1mm deviation can be used.

TIP: If the CG or volume are off by an amount greater than the tolerance check for self intersections in the solid and if the source of the geometry was mirrored data.



Translate the Data

The UG part can be translated using Theorem Direct, STEP, or IGES.

Theorem Direct UG to Catia

TIP: Use the Theorem surface optimization tolerance to reduce file size

Translate with the surface optimization tolerance set to .0001 for inch parts. The general rule is to use an order of magnitude tighter than the users machining tolerance. If left at the default value surfaces such as variable radius blends, will be b-spline approximated at the parasolid default that can result in larger files in Catia. From the command line use add the option “surfopt .0001”.

TIP: Use the mask to turn off unnecessary layer data

The Theorem mask file is a simple ASCII file used to control translation. To turn off a layer the user can create the file (e.g., layeroff.msk) with the following line:

OFF LAYER 11

See the Theorem documentation for more details on how to use the mask file.

Make sure blanked data in the file is not desired, by default blanked data is not processed. Use the mask file to select blanked data.

TIP: Use the Retain assembly structure option to maintain UG assemblies

If the Unigraphics parts contain any assembly structure, then selecting this option will create Detail/Ditto structure in the Catia model. The default is to explode the assembly structure into a flat single level structure. If running from the command line add “ditto” as a parameter. Remember the earlier caveat for Catia model size. Sometimes translating individual components may be necessary to avoid Catia model size limits.



UG to STEP and STEP to Catia

Make sure the user followed the steps to prepare the file.

TIP: Use the Face/Edge b-spline approximation tolerance

Translate with the Face/Edge b-spline approximation tolerance set to .0001 for inch parts the general rule is to use an order of magnitude tighter than the users machining tolerance. If left at the default value, surfaces such as variable radius blends, which must be b-spline approximated, will be output at the tightest tolerance resulting in larger files in Catia. A default file must be created from the STEP user interface in order to change this value. Select the UG to STEP direction and then proceed to the Translation Options. From this menu you will be able to change the tolerance. Be sure to save the default file if you will be running the translation from the command line.

TIP: Use the default file to turn off unnecessary layer data

Limiting the amount of data to translate will speed up translation as well as make it easier for the receiver to understand. When using Unigraphics STEP one way to accomplish this, turn specific layers on or off to enable or disable translation. A default file must be created from the STEP user interface in order to change this value. Select the UG to STEP direction and then proceed to the Translation Options. From this menu you will be able to select the layers to translate by disabling and then enabling layers. Be sure to save the default file if you will be running the translation from the command line.

TIP: Use the interactive UG version of STEP to flatten assemblies

The STEP translator does not offer a command line or default file option to flatten assemblies at translation time. If a flattened assembly is desired, access STEP from interactive UG and select all objects from the loaded assembly for translation.

TIP: Set the Catia DCL STPCAT_EXACT_SOLIDS_CREATION = TRUE

By default the Catia translator will create Volumes from Solids at translation time. Part of the reason for doing this is to reduce the Catia model file size. If the user wishes to get Solids as a result of the translation the DCL must be set first.



IGESTIP: If the user wants to translate wireframe data only from a solid part

In the IGES menu under 6. Preprocessing options -> 8. Entity selection, set all Surface and Solid types to OFF. Also turn Curve type, 7. All Solid Edges, to ON.

TIP: If the user wants to translate Drawing Data only

In the IGES menu under, 6. Preprocessing options -> 8. Entity selection, set all Surface and Solid types to OFF. Also turn either Curve type, 6. Solid Edges on Drawings or 7. All Solid Edges, to ON. NOTE: Solid Edges on Drawings will limit the number of edges that are translated to the IGES file, to those which appear on the drawing or its views. All Solid Edges will cause all edges in the part to be translated. Since All Solid Edges is a superset of Solid Edges on Drawings, Solid Edges on Drawings can not be turned OFF when All Solid Edges is ON. In addition, turn Views Visible type, 3. Segmented Views Visible (402/19), to ON for best results on the receiving system. NOTE: IGES entity 402 form 19 is a gray page entity and may not be supported by the receiving system. If this is true, leave 3. Segmented Views Visible (402/19) set to OFF. You will lose information controlling entity view dependent edits of color, font, or width for individual segments of that entity. An example is an edge entity is partially hidden and is invisible or dashed. Without the 402/19 entity, the invisible/dashed information is lost and the entire entity shows up as solid in the receiving systems view.

TIP: If the user wants to translate drawing data only from an assembly part

In the IGES menu under, 6. Preprocessing options -> 8. Entity selection, set all Surface and Solid types to OFF. Also turn Curve type, 7. All Solid Edges, to ON. NOTE: Solid Edges on Drawings will not work with assembly parts. In addition, turn Views Visible type, 3. Segmented Views Visible (402/19), to ON for best results on the receiving system (above NOTE applies). The user must also set, 6. Preprocessing options -> 10. Entity mapping -> 10. Assembly, to either Expanded Grouped Geometry or Expanded Ungrouped Geometry. If Patterns which contain geometry with View Dependent edits exist in the part, also set, 11. Pattern, to either Expanded Grouped Geometry or Expanded Ungrouped Geometry. NOTE: Use of the Expanded Geometry options will cause the resultant part on the receiving system to be a piece part. That is, the nested Assembly structure will be lost. NOTE: This method of translating Drawing Data from Assembly parts will only work for Assemblies with components one level below the top. All View Dependent edits below that level will be lost.



General translation tips

In general translating the file into a separate directory for each model, STEP, or IGES file received will prevent the overwriting of assembly or component files, and will also give the user a better idea of what files resulted from a particular translation.

All of these products run from the command line and can easily be called from a script, making large numbers of files easier to handle.



Check Fatal Errors

Each of the translators output a log file. See each user guide for naming conventions etc. In general the Theorem log file can be scanned for the word 'Error', STEP can be scanned for the word 'Contains', and IGES can be searched for the summary at the end of the log file. Fatal errors will usually be shown by a loss of data.

Alternate Methods

If translation with one tool fails, try another. Since translation should require the least amount of user time, try one of the other translators if they are available. If another translator does not work, look further into the errors in the translation to see specifically what failed. Check if geometry is corrupt from the sending system or can be modified to improve translation. As an example, in some extreme cases removing a blend from a solid in Catia will allow the basic solid to be translated to UG. The blend can be added in UG. Tests have shown that this can be successfully done without impacting the original CG and Volume.

Generate UG Validation Data

See the UG to Catia process for Details.





Catia to UG Process

Prepare / Organize Data for Translation The exchange from Catia to UG starts with the model file. There are several ways to generate data for exchange in Catia depending on the users' access to a Catia license, or the working relationship with the supplier. Here are a few of the details to create files for Exchange from within Catia. The following steps will help in the exchange of geometry data. The Catia user should look into the following utilities to gain a better understanding. CATUTIL->CATMOD, CATUTIL->CATCLN, CATUTIL->CATEXP.

FILTERING

Filtering drawing data from the CATIA file and general cleanup can be accomplished by performing the following operations on the CATIA model:

1. Remove all elements from NO-SHOW/NO-PICK

2. Convert all SOLIDMs to SOLIDEs, where possible, by using SOLIDE/MODIFY/TYPE or the CATSOE utility.

3. Generate Volumes from SOLID-E and delete SOLID-E in all workspaces

4. Replace dittos placed into workspace using symmetry (left handed coordinates to use right hand coordinates) (STEP)

5. Explode all dittos and composite curves

6. Delete all unused details

7. Delete all DRAW geometry before STEP translations

AUXVIEWs DRAFTs Draw geometric elements Dimensions/text Symbols Symbol occurrences Draw dittos Draw details Schematic elements (logical lines and connectors) (*)

8. Delete all filters

9. Apply the “ALL” filter to the master workspace

10. Delete screens/windows/transformations

11. Delete comments



12. Delete UDBs/Application elements and sets

13. Delete logical lines (piping, schematics, and so forth)

14. Delete all CATIA

NC sets Robotic sets TASK sets Kinematic sets Nesting sets

15. Invoke IDENTIFY/UPDATE and IDENTIFY/RENAME+ALL

16. Delete all geometry not directly involved in machining the part

Note: All items above can be accomplished by using native CATIA functions..

PART MERGE

Part Merge can also be used to filter out unnecessary geometry very quickly. Do this by merging only the desired geometry into a new part. An example of this would be to merge only the exact solid information of a part into a new part.

CATMOD

CATMOD can be used to prepare the model for translation before transferring a CATIA model to another CAD/CAM system. CATMOD has the capability of maximizing details, deleting draw elements, and removing unused details. CATMOD may also change mapping of entity types from one type to another.

CATCLN

CATCLN is used to prepare the model for translation by “fixing” corrupt geometry, such as zero-length geometric elements. CATCLN can be accessed in CATIA by selecting UTILITY/CATCLN. Or by running /CATCLN from the command prompt. Running this operation will clean up some of the problems in Catia model geometry before translation.



Model Preparation Best Practices

TIP: A DCL can be used in conjunction with CATMOD to convert pipes to SolidE

STEP or Theorem direct translators will not recognize Catia pipes in their native form. If these entities are desired they need to be converter by Catia first.

TIP: Update Catia model

In Catia it is possible to change the operations (CSG) which create the solid, but may not be reflected in the solid until an update is done. Make sure that all model files have been updated before translation.

TIP: Convert SolidM data to SolidE data before translation

SolidM data or mock up solids result in facetted b-rep solids in UG. Facetted b-rep solids are cumbersome to use in UG because they are usually solids with many faces wherever there is some type of radius. SolidM data is an approximated solid used by Catia to speed visual operations and should not be used as input into operations such as machining where the exact model is necessary.

TIP: Filter out unnecessary data



Data Validation ErrorsBe sure to check all messages and log files from the CATCLN and CATMOD processes. Also if the user knows of other tests that can be run to validate geometry they should be run now. Address critical issues related to the Catia Geometry Rules section of this before proceeding with translation.

Creation of CATIA Verification Check Data

CATIA check data can be used at several points throughout the process. First, it is used to validate that the model preparation process has not modified the CATIA geometry. Second, it will be used to validate the geometry once it is in Unigraphics. Each site can set the acceptance standard and what the criteria should be. The values below are an example of such criteria.

Cloud of Points

The cloud of points are points that are projected to the critical areas of the part, which include the following:

Mating areas Specific blended surfaces Pockets

The cloud of points can be created manually in CATIA by using the POINT/PROJECT/REPEAT function.

On the CATIA side, the maximum deviation tolerance will be .0039 in or .1 mm. If points fall out of this tolerance range, recheck that the points were created correctly. For example, a problem might be creating points on SolidMs geometry before it was converted to SolidE and then STEPed out (although, procedurally, this should never be done).

Volume, CG, and Surface area.The volume of a closed body is a good high-level indicator if the part has changed through translation. The volume, CG, and surface area can be obtained by running BDEBUG, or by interactively selecting the Analysis function-> Inertia-> Compute Absolute then pick the solid. The information can be placed in a text file using the print option. One criterion for CATIA-UG allowable deviation for the volume or surface area metric is .1% of the original volume or surface area. For CG .0039in or .1mm deviation can be used.



Translate model

The CATIA model can be translated using Theorem Direct, STEP, or IGES. The following Hints may aid in translation of any of the methods.

Theorem Direct Catia to UG

TIP: Translate with the Parasolid Tolerant Modeling factor set to “3”

The tolerances used to create geometry in Catia can differ drastically from those required by Unigraphics. For this situation, Unigraphics has tolerant modeling, placing a band of tolerance around all of the edges to allow the data to be used. The tolerant modeling factor of 3 has shown the best success for getting Catia geometry into Unigraphics. From the command line the following parameter would be added “pstolmodel 3”

TIP: Use mask files to filter or turn on geometry

Use the Mask file to further filter the translation for turning off of layers, translating solids as CSG, facetted or BREP.

Note: Sometimes data in Catia may be in NOSHOW mode, Default setting will not process NOSHOW data. Use mask file to turn on NOSHOW data in the following manner.

ON NOSHOW

TIP: Turn off Parasolid checking for hard to translate solids

This option is only recommended as a method of last resort. The resulting solid will more than likely have a Parasolid fault that will need to be addressed. For those users who cannot explain why a solid will not translate into UG, this option can be used to allow the user to use the Unigraphics Examine Geometry tools to investigate the problem with the model.



Catia to STEP and STEP to UG

Make sure the user followed the steps to prepare the file.

TIP: Surface and Wireframe data

If STEP is accessed from ugmenu under option 2, translation control option 7 , the Modules option defaults to Solids and Product data. This setting will only translate the solid and product data found in the STEP file. If surfaces and wireframe are desired, select option 7 and turn on wireframe and surfaces. Be sure to save off the default file if running from the command line rather than submitting the translation from the user interface.

TIP: For STEP to UG use tolerant modeling

If the user is running standard user defaults the fault correction method will be set to tolerant modeling and will not need to be changed.



IGESTIP: Translate an Assembly IGES file into UG

If the user wants to translate an Assembly IGES file into UG, and the Sub-figures in that file contain text, which he wants to appear in the top level UG part:

In the IGES menu under, 7. Postprocessing options -> 12. Entity mapping, set 6. Subfig Text/Dimensions TO Visible- Component and Assembly Parts. NOTE: The translator will create a reference set in the component part containing both the text and geometry, then include that reference set (rather than the component part itself). UG does not support display of component part text in the top level part, but it does support display of reference set text in the top level part.

General Tips

In general, translating the file into a separate directory for each, model, STEP, or IGES file received will prevent the overwriting of assembly or component files, and will also give the user a better idea of what files were the result of a particular translation.

All of these products run from the command line and can easily be called from a script which can make running large numbers of files easier to handle.

Check Fatal Errors

Each of the translators will give a log file as output. See each user guide for naming conventions etc. In general the Theorem log file can be scanned for the word 'Error', STEP can be scanned for the word 'Contains', and IGES can be searched for the summary at the end of the log file. Fatal errors will usually be shown by a loss of data.

Alternate Methods

If translation with one tool fails, try another. Since translation should require the least amount of user time, try one of the other translators if they are available. If another translator does not work, look further into the errors in the translation to see specifically what failed. Check if geometry is corrupt from the sending system or can be modified to improve translation. As an example, in some extreme cases removing a blend from a solid in Catia will allow the basic solid to be translated to UG. The blend can be added in UG. Tests have shown that this can be successfully done without impacting the original CG and Volume.



Appendix AWe consider each of the data types in the following paragraphs.

Simple Graphics DataVector-oriented 2D graphics formats are adequate for exchanging graphical representations of engineering drawings and other types of illustrations. Simple graphics data is easy to exchange using well-known standards such as CGM, PostScript, and various bitmap formats. The simplicity and broad acceptance of 2D graphical formats explains the ease with which images and illustrations can be transferred between PC applications like MS Word, PowerPoint, and Excel, or viewers such as Netscape and Internet Explorer. When the user needs to communicate a graphic representation of a part, the creation of CGM, gif and tif images need to be considered an appropriate solution, especially if the receiver is not required to make any changes to the data. This data can be easily created from within UG and Catia, and 3rd party tools such as xv can be used to create this data.

FacetsFacet data is often used for high-end graphics applications and for spatial studies of fit, clearance, and accessibility and to drive one of the many Rapid Prototyping technologies. Many systems for visualization and analysis of large assemblies are driven entirely by facet data. The number of facets used can be adjusted to make sensible tradeoffs between accuracy and performance. This type of data is generally easy to exchange. Common formats include VRML, STL (stereolithography files) and various graphics file formats such as Inventor. The most popular method of creating facet data to be exchange from UG is to use the Rapid Prototyping Interface found in the Unigraphics File->Export_>Rapid_Prototyping. Catia facet files can be created by using the STL operator found on the keypad choices. There are also interfaces available to create facets from Catia models or UG parts for UG/Reality (Division's Dvise) software. In some cases, the best method is to exchange the solid data directly. It can be converted to the appropriate format for DPA in either Unigraphics or Catia.

GeometryShape information is central to many engineering and manufacturing applications. The most basic building blocks for representing shape information are geometric entities — points, curves, and surfaces. Points are so simple that they do not warrant any further discussion. The curve types generally available are:

Line (i.e. straight line), Circle, Conic section curves (ellipse, parabola, hyperbola),A spline curve, usually a non-uniform rational b-spline (NURB) curve, Similarly, the surface types typically available are Plane, Circular cylinder, Circular cone, Sphere, Torus, Surface of revolution, Extruded surface, Offset surface, Some sort of free-form surface, usually a NURB surface

This is roughly the set of geometric entities specified in standards like IGES and STEP, and (more importantly) is roughly the set of geometric entities supported by most popular systems. Simple engineering geometry (lines, circles, planes, cylinders) has been standardized for hundreds of years, and is easy to exchange. In recent years, with the almost universal adoption of NURBs, free-form geometry has also become easy to exchange, although there are sometimes problems because different systems have different limits on the mathematical degree of NURBS curves and surfaces. Because of this commonality, of geometry forms, exchanging curve and surface data between systems generally works very well. Conversely, market demand for good basic data exchange facilities and “open” systems deters vendors from deviating too far from this data model, so it is likely to remain quite stable in years to come. Geometry data can be exchanged very effectively using standards such as IGES and STEP. STEP is somewhat preferable because the geometric objects are more rigorously defined.



Boundary Representation TopologyMost systems use some form of boundary representation (b-rep) in which curves and surfaces are combined together to describe (solid or sheet) bodies. The basic topological entities are vertices, edges, loops, faces, shells and bodies. They record various types of adjacency or connectivity relationships, as illustrated in the figure below.

So, for example, we might store information indicating that two faces are adjacent in the sense that they meet along some common shared edge. Note that this is logical information, and in fact the two faces are typically allowed to have a small gap between them, provided this is less than some tolerance. Problems arise when exchanging topology information because different systems use different tolerances when deciding whether or not two faces should be considered adjacent. The gap between faces might be within the tolerances of one system, but outside the tolerances of another, thereby contradicting the topological information indicating that the two faces are adjacent. In other words, we arrive in a situation where the geometric information and the topological information are inconsistent. Parasolid creates models to very tight tolerances, so exporting from Parasolid to another system typically works very well. To import models from a less precise system, Parasolid has a special “tolerant modeling” facility that allows it to handle models that are less precise than the ones it typically produces itself. The tolerant modeling innovation helps considerably, but topology problems still arise when transferring solid models between systems using standards such as STEP and IGES. Using the same modeling kernel in the systems that need to exchange solid models can eliminate these problems. For example, exchange of solid models between Unigraphics, Concentra ICAD, and SolidWorks operates flawlessly because they all use the Parasolid kernel.

Drafting Annotations & SymbolsDrafting annotations (notes, labels, dimensions, crosshatching) are actually quite difficult to exchange effectively. The problem is that they are represented in quite different ways on different systems. In particular, many layout problems arise from font differences. Both IGES and STEP (not in production) have facilities for exchanging drafting annotations, but it is surprisingly difficult to transfer drawings between systems and have them look identical afterwards. Of course, if identical appearance is all that’s required, simple graphical formats (CGM, PostScript) can be used instead, though this loses all the structure and “intelligence” in the drawing and makes it fairly difficult to edit in the receiving system.

Data OrganizationData organization structures include groups, layers, categories, and assembly structures. Provided the participating systems have equivalent capability for representing organizational structure, exchange should work smoothly, since this is logical data that is not subject to precision problems that occur with



floating point data. Most contemporary systems have roughly equivalent facilities for representing layer, group, and assembly structures, and these structures are well supported in IGES and STEP AP214.

Associative RelationshipsIt is often useful to establish associative parent-child relationships between objects owned by the two systems. This is difficult to achieve if the two applications share data via file transfer, rather than by data file unification. The problem is that file transfer is a “delete and recreate” operation with a very coarse level of granularity, and it is difficult to keep child objects properly attached to parents who are continually dying and being reborn en masse. The situation can be improved by using incremental file transfers (transferring only the objects that have changed) or by requiring the sending system to assign persistent identifiers that can be used to track objects as they are deleted and recreated.

Feature and Parameter DataFeature and parameter information is difficult to exchange, but fortunately this does not have a great impact on applications effectiveness.

A feature can be thought of as a parameterized collection of faces and edges that is to be attached to some target body. The feature might be positive (boss, pad, rib) or negative (hole, pocket, groove). Features can be loosely classified as:

Form Features: Hole (simple, counterbored), pocket, boss, pad, etc. Body Features: Block, extrusion, free-form bodies Operation Features: Blend/round/chamfer, taper, offset, hollow, etc. Enumerative Features: Circular and rectangular arrays

In some systems, almost any associative object is referred to as a feature, but this obscures the term, so we choose to use it in the more specific sense described above.

The main value of features is in model editing — the user changes lower-level objects and relies on the system’s associativity facilities to propagate this change throughout the rest of the design and any attached applications data. This technique affords tremendous editing leverage — global design changes can be introduced with very little user input. Furthermore, the parent-child relationships between features can serve to capture and enforce simple engineering rules.

Design features are very rarely used in applications because the feature structure introduced during the design stage is unlikely to be the one needed for applications.

There is currently no means of translation that will retain feature data.



Appendix B

Tools

Since there is no one tool which handles all of the types of data that may be exchanged between the two system you must select which tool or combination of tools best meets your data requirements. Since geometry and specifically Solid Geometry is the most commonly requested data the general recommendation is to select either STEP neutral file exchange or the Theorem Direct translator, or both.

Data Type PreferredSolution

AlternativeSolutions

Comments

Simple Graphics Data

CGM TIF, GIF Select whichever format is easiest for the user to view.

Facet Rapid PrototypingInterface (STL)File generation export from UG

only.

STEP Alternate solutions exist such as direct facet conversion for

Users of Unigraphics Fly Through software from

Division. STEP will transfer the Mockup solid of Catia

into UG as a facetted BREP.Geometry STEP/Theorem

DirectIGES/VDAFS Requires knowing customers

overall needs. STEP offers a broader list of exchange

partners, Direct offers fewer translations.

BREP STEP/ Theorem Direct

None See comments above

Drafting Annotation,

Symbols

IGES DXF Go this route if the drawing data needs to be modified or updated. If only for viewing

see Simple Graphics Data methods above.

Data Organization

IGES STEP, Theorem IGES offers the most robust data organization support today including groups,

layers, and assembly structure and color. STEP is getting

closer, but not fully mature.Associative

RelationshipsNone None

Features None None



Product Descriptions

IGESIGES is the work horse translator in the industry today. It is a mature standard. We support most of the current standard (5.3). Solid exchange via IGES is planned for an upcoming UG release.

We have several projects underway to improve our IGES offering. First we have a performance improvement effort underway to reduce the time-to-translate an IGES file. Second we are pursuing an ease of use - improved user interface capability. This will enhance the user’s ability to set parameters and options more effectively in a much friendlier manner. And third we are pursuing more robust geometry processing, especially of suspect or marginal data.

For Catia exchange IGES is the most robust of the translators as far as coverage of the most types of data including: Geometry, Drafting, Data Organization, and Assemblies. IGES may not be the first choice since Solid Geometry seems to be the highest priority of many users. If Geometry with drawings that can be updated is a requirement IGES is the most likely choice.

STEPSTEP is the emerging standard within the industry. STEP is made up of “application protocols” . We support AP203 and AP214. These are the major geometry oriented standards used within our industries. Our STEP AP’s support wireframe, surfaces, solids, configuration management, and assemblies.

STEP is the correct product for situations where the user has specific commitments to be standards based, is working with a partner who prefers a standards-oriented solution (GM and Boeing are examples), or where the data has to be sent to numerous other partners. Another scenario where STEP is a viable solution is when the target system is unknown.

More detailed information on STEP can be found the STEP Primer, as well as the STEP Position Paper found in the Product Information Matrix for Data Exchange.

The Unigraphics STEP translator has become one of the most successful STEP translators as evidenced by testing by PDES and ProSTEP. For users who need a translator with flexiblity and to exchange Solids STEP is your choice.

VDA FSVDA FS is a German standard. The Unigraphics Solutions VDA FS was developed and is supported by Unigraphics Germany. A main use in the US for this translator is interfacing with certain machine tools developed and built in Europe.

The VDA translator is available via the sales order system. The product is shipped from the Germany office. You can contact Jim Mohan (+1 314 344 5330) or Uli Kohler (+49 22 120802200) if you have questions.

VDA FS is considered the German IGES and is used heavily in the movement of surface data between Catia and Unigraphics.



Theorem DirectBoth STEP and Theorem provide excellent data exchange capabilities, and from a geometry perspective, are equal. Many of our large customers who have to do mass migration of data between Unigraphics and Catia have successfully made use of the Theorem Catia direct translator.

Other issues to consider for a given situation are:

Direct translations work with native format, reducing the need for a STEP translator on the partner system Text and dimensions are available with Theorem’s V2.1 release (May 1998)



Appendix C

Common Catia Terms and Rules for the Unigraphics User

This section will describe some of the common Catia terms associated with exchanging data with Catia.

SolidE- SolidE is also known as a Catia exact solid. The exact solid is basically the equivalent to the Ungraphics b-rep solid.

SolidM- SolidM is also known as the mock up solid. Mock up solids are used frequently in the Digital Pre Assembly process and are found in Catia model files because they take up less space than exact solids. The mock up solid is an approximated solid and is very similar to a Unigraphics facetted solid used in the assemblies applications. Currently both the STEP and Theorem translators will translate these into Unigraphics b-rep solids, creating a face for each of the facets. These solids are typically cumbersome to manipulate and should not be used for downstream applications such as machining since they are approximations of the Solid. The Theorem translator does allow for the translation of the mock up solid directly into the Unigraphics facetted solid used by the advanced assemblies applications.

CSG - Constructive Solid Geometry is the history of the operations required to create a specific solid either SolidM or SolidE. The history can consist of primitive boolean operations and procedural constructions. Direct translators usually try to recreate the SolidM based on the construction history using primitives. If procedural constructions are part of the history such as filetting operations, the translation will not be able to recreate the construction history and the solid should then be processed as a facetted or facetted b-rep Solid. A direct translator will attempt to handle the SolidE in its b-rep form even if a CSG is present. Neutral file exchange such as STEP will handle the translations as in their final forms of SolidM or SolidE resulting in a facetted b-rep solid or b-rep Solid in Unigraphics. Neutral file exchanges do not support the CSG representations.

Isolated Solid- A solid which has no CSG associated with it.

Volume- A volume is a ruled combination of closed skins.

Skin- A ruled combination of faces

Face- A ruled combination of closed series of edges (loop)

Edge- A curve delimited by two vertices and lies on a surface

Detail-Similar to a UG part, or assembly

Ditto- Similar to a UG component

NOSHOW- Similar to UG blanked data

Catia Geometry Rules found in Catia using the STANDARD MODEL Function.

All tolerances in Catia are driven by the MODEL DIMENSION. The model dimension is used in calculation of the ratios which define the tolerances. Any entity created with in a model is computed in the context of the current tolerance system. Any change to the tolerance value after an entity has been created will risk degenerated elements or elements over the infinity value. It is wise to ask the sending or receiving site what their MODEL DIMENSION is and apply it uniformly to all models.

Catia Model Dimension = Set by site, common value is 10,000mm for aerospace sites



Identical Points Tolerance = 10-7 X Model DimensionIdentical Curves = 10-5 x Model DimensionIntersection Projection = 10-2 x Identical curvesInfinity = 106 X Identical curves

An entity cannot be smaller than the Intersection Projection.An entity cannot be larger than Infinity.Models cannot be merged with different geometric standards.

Face rules:

A face cannot be thinner than the Identical curves value.A face cannot be periodic. Catia creates two faces around a cylinder.In a face loop, every edge must not be separated from adjacent edges by more than the identical curves value.

Edge rules:

An edge may be created by a projection of a curve on a surface, if the distance between this curve and the surface is greater than the identical curve's value.

If two adjacent edges are closer than the identical curve's value, you can merge these edges.


Catia_Best_Practices

Documents

ug validation data

symmetricmirrored data

ug process

catia process

data validation errors

theorem direct ug

simple graphics data

theorem direct catia