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Creating a TopoDS_Solid with voids

Ben Hollingsworth's picture

I'm trying to create a TopoDS_Solid (an extruded profile) with a handful of void openings cut from it.  According to several places in the online documentation, the first shell specified for a new solid is the outer shell.  Subsequent shells added to this solid are considered to be voids or hollows within that first shell.  I think I'm creating the solid the right way before exporting the file to STEP, but every STEP viewing program I can find imports all of these shells as solid shapes, not as a single solid with multiple voids.  What am I doing wrong?  Here's a simplified version of my code (the actual code is far too long & involved to post here).

BRepBuilderAPI_MakeSolid solidb(outer_shell);
for (all void openings)


shape_tool->SetShape(my_label, solidb.Solid());

Ben Hollingsworth's picture

I should point out that I've verified that the resulting solid does have multiple shells, according to this check:

    TopTools_IndexedMapOfShape map;
    TopExp::MapShapes(solidb.Solid(), TopAbs_SHELL, map);

    printf("solid contains %d shells\n", map.Extent());

For some reason, this isn't getting exported to STEP in a manner that shows them as voids.  I'm using STEPCAFControl_Writer to Transfer to STEP using the default mode, which is STEPControl_AsIs.  I tried specifying STEPControl_ManifoldSolidBrep, but with identical results.

Ben Hollingsworth's picture

By analyzing the resulting STEP files, it appears that OCCT is creating my STEP element as a BREP_WITH_VOIDS.  This seems reasonable, but doesn't work in any STEP reader I've encountered.  All of the working STEP models that I can find create both their outer shell and their void shells as multiple MANIFOLD_SOLID_BREP entities.  Is there a way that I can tell OCCT to create the latter?  As I mentioned earlier, passing STEPControl_ManifoldSolidBrep to STEPCAFControl_Writer.Transfer() still creates BREP_WITH_VOIDS.

Ben Hollingsworth's picture

Since nobody is apparently able to respond here in the forums, is this a question that could be answered through paid technical support?  We need to get this problem resolved, and we're willing to pay for help if necessary.

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Dear Ben,

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