Extracting Geometry from CGR files

March 8, 2021 Iouri Apanovitch

The CGR (Catia Graphics Representation) is a light-weight format that is commonly used for geometrical data exchange among OEMs and suppliers. CGR is a tessellated file format similar to STL, which you might be more familiar with. I.e., CGR data is a collection of flat triangles, rather than exact surfaces and edges, as would be in the CATPart file.

The CGR files are much smaller than their CATPart or CATProduct counterparts. Also, CGR data is sufficient to perform most of the design review tasks, such as measurements, cross-sectioning, interference analysis, etc.

However, geometry data in this format cannot be directly extracted or referenced in a CATPart, which creates difficulties when doing design work in context with CGR models.


To do so, you must use some "tricks", which I will present in this post.

Trick #1: Using Measure Item tool

This method only allows extracting points.

1. Insert the CGR file into a new or existing CATProduct.

 

 2. Start the Measure Item tool and select a point or a curve you want to extract. (Make sure Exact else approximate is selected as the Calculation mode.)

 

3. Click Create geometry button. Select whether to insert the extracted geometry in a new part, or in an existing one.

 

4. If a curve was measured, select whether to extract the 1st endpoint, the 2nd endpoint, or both.

 

5. The points get extracted into the CATPart.

 

Trick #2: Using DMU Optimizer workbench

With this method, a CGR file is exported as a surface model.

  1. Insert the CGR file into a new or an existing CATProduct and activate the DMU Optimizer workbench (DMO license is required).
  2. Either Offset    or Silhouette   tool can be used:
    • The Offset tool exports the tessellated geometry as-is, while Silhouette tool allows geometry simplification by reducing the number of triangles in the tessellation
  3. Select, for example, the Offset  tool and select the CGR model.
    • Make sure the Offset value is 0

 

  1. Click Save and save the result as the .model file

 

  1. Open in CATIA the .model file from the previous step.
  2. Double click on *MASTER to expand and copy *SET1

  1. Open a new CATPart and Paste Special the copied set as CATIA_RESULT into a geometrical set.

 

  1. Each triangle from the tessellation is copied and pasted as a separate surface.

 

  1. Use the Join tool from the Generative Shape Design workbench to join all the separate surfaces into one quilt-like surface.

 

Lastly, keep in mind that CGR geometry is never as accurate as that in a CATPart file. If this represents an issue in your design work, request a CATPart file instead.

 

About the Author

Iouri Apanovitch

Senior Technical Training Engineer<br><br>As a senior member of the Rand 3D team with a doctorate degree in Finite Element Analysis (FEA) and over 35 years of experience, Iouri provides design, consulting, and training services to those in the aerospace, automotive, electronics, and consumer goods industries. Iouri is a seasoned pro in 3D parametric design and prototyping using knowledge-based engineering methods, and has worked on a wide range of projects including BOM automation, CMM points generation, automated 3D annotation creation, and die tooling automation design. He is also a sought-after instructor and holds the designations of both CATIA Certified Professional (Expert level) and CATIA Certified Instructor.

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