I don’t understand what distinguishes a “closed_shell” from a “manifold_solid_brep”. In Rhino you have closed single surfaces (like a sphere) and closed polysurfaces (like a box). Both are considered closed breps (a single surface is also a brep). From the message from DS support above, it sounds more like what is needed is that single closed surfaces like spheres need to be exported as closed_shell and not manifold_solid_brep…
Rhino is not a solid modeller. It does not destinguish one from the other, but other software do. There has to be more options in the step exporter just like when you export to dxf you have options what objects in Rhino should be treated like what objects in the DXF.
Same should happen with STEP exporter. Currently the only option is to choose between the three APs. But you cannot configure the exporter to treat the closed polysurface as a CLOSED_SHELL instead of a solid.
Rhino does export as CLOSED_SHELL entities. A MANIFOLD_SOLID_BREP is an entity that contains a list of shells. If your 3dm data conains any solids, each should show up as a CLOSED_SHELL entities in a MANIFOLD_DOLID_BREP’s shell list.
I don’t see this as a Rhino issue. It is standard practice to represent a solid as a closed_shell which is referenced by a manifold_solid_brep. If you have a STEP file containing a solid, and it reads into Catia the way you want, please send it to me. Maybe I can figure out the difference and give an option to do it that way.
I’m sorry. I assumed you have seen the behavior that you are asking for and would have a file that exhibits it. The response you posted from Catia does not indicate to me that there is a problem with the Rhino STEP file.
Not me, and it is not about liking it. Volumes (closed surfaces) are used in Catia as filters, whilst solids cannot be used. Catia is bad at boolean unions so they are done in Rhino. And the import results in solids.
I have to use weird hacks to make them Volumes again, which could not even be necessary if it resulted in Volumes in a first place.
I caught DS R&D in bullshittery.
First they stated they can import closed polysurface objects as closed volume objects in CATIA. Then when I asked for a exmple file, they stated “STEP does not differentiate between closed volume and solid”.
Please accept my appology, although I was deceived by DS crap of an R&D team.