support for IGES constructive solid geometry entries?

I was hoping to create some simple CSG shapes using the CSG primitivies of IGES.
I've only tried FreeCAD, which doesn't seem to like to view them. I asked on
the FreeCAD forums and they say everything is BREP these days and there is no
hope of viewing CSG trees as described by IGES.

However, in the OpenCASCADE source I've found some support for (for example)
IGES entity type 154 (solid cylinder). Does OpenCASCADE support these
primitives? Do any other viewer programs (solidworks)?


Forum supervisor's picture

Hello Britton,

Open CASCADE Technology (OCCT) imports IGES data in two steps: at first it transfers the file into a model in memory, then it translates the model into a OCCT representation (Shapes etc). On the level of the model, most of data you can find in the IGES file are supported. However not all of them are converted into OCCT shapes during the second phase of translation. In particular, in case of CSG model only the final BRep representation of the result of CSG tree is translated into OCCT shape, if it is recorded in the file. All intermediate primitives that compose the CSG tree are not converted to shapes.

However, since all data and operations are available in the model, it is quite possible to create a custom extension of the standard interface to support reading in the CSG data and re-constricting the complete tree of primitives and operations in the OCCT environment. Such sort of interfaces were already created by OPEN CASCADE company in the past, for example, for transferring CSG models from EUCLID 3 software to CATIA V4 and V5. If you are interested in our custom development services and wish to order such project please contact us at

Best regards,
Forum Supervisor