Create a Watertight Object from Meshes

Similar topics have been discussed before but I haven’t been able to find the correct answers. I have a CAD model exported from other CAD softwares. The model is in DWG which I import in Rhino. The model comes as meshes with a whole lot of triangulation. Now I want to convert it to solid polysurfaces without triangulation which are closed and watertight. The model by itself has been exported from another BIM software so the elements are all proper. I ideally should not be needing to stitch anything.
How do I do it ?

Is it not possible to get the file as a STEP or IGES instead?

@ftzuk , I haven’t tried that and could try it, but the main objective is to have a model into Rhino that doesn’t have any triangulations. Will the STEP model provide that ?

STEP won’t have any triangulation.

It depends what is exported at the other end. In the worst case they convert mesh faces to surfaces and then the step consists of triangles

If the model is coming from Revit and is exported to DWG, its possible it is exported as meshes. There is a setting in Revit that is buried in the options that will force it to export nurbs solids where possible. If the object is a toposurface it cannot be exported as a solid (ACIS object), and will always be a mesh (triangulated)
https://help.autodesk.com/view/RVT/2022/ENU/?guid=GUID-CE5C1481-40BE-4503-A55C-25B0BC0F817B

@cdordoni So the issue here is I can directly export from Revit as ACIS solids which comes perfectly as Polysurfaces. But there is some cleanup and stuff which needs to be done in Max and then the model is ready to be exported.
I also tried STEP converter online but that too imports finally as Mesh only in Rhino. So no luck with that @ftzuk.
Somehow I think this problem has been persisting since long as I could see that on other forums as well. Seems even if I select No Triangulation while exporting FBX from Max, it still does create triangulated meshes. And its not an issue with Rhino import. Because I tried with online FBX viewers and those too show the same.

Now the next thing I am trying to do is to see if Grasshopper can help me deconstruct meshes and reconstruct as Polysurfaces. Let’s see.

Can you share some of your geometry or at least a picture ?

Can try this:
ExportMaster for Autodesk® Revit® - IGES® | Autodesk App Store

But yeah I’ve neved used Revit so not sure. I thought it would have STEP & IGES export as part of the program.

Sorry, I didn’t share an image before. Here it is.

But happy to tell you all that I was able to crack the problem using Grasshopper. See conversion images too:


Although a small part of the model. 3 meshes have been added. Next step is to see if all the meshes can be added and whether it gives any errors.

Attached is the script too.
Gh script for Mesh to Nurbs.gh (14.6 KB)

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Final one:


Fairly successful.