Which file format is Rhino most reliable at importing from?

We are 9 months in to developing a web app in Azure that harnesses both Autodesk Forge and Rhino.Compute at the core of what it does. By and large things are good. At its core is this fundamental activity:

  1. Our app takes a part file from our legacy library of Inventor part files (.ipt) and passes it with new parameter values to the Forge.
  2. The Forge updates the part’s parameters and exports the resulting shape in a file format that Rhino can open. (very slow)
  3. This file is sent to Rhino.Compute which opens it and returns its breps as a byte array.
  4. Our app stores the resulting breps in our database cache for future reuse so in future steps 1 2 and 3 can be bypassed.

We are having problems with the reliability of step 3. When it works it is great and very fast. However we need to decide on the file format to export from the Forge that gives Rhino the greatest success rate in opening the file. We started by exporting STEP format but found that Rhino fails to import STEP files for even quite simple files (see this post). As a workaround we changed strategy and tried exporting DWG but have now discovered that our Rhino6 is also failing to import these files sometimes as well. I attach an example.

SmallCylinderWithTinyCentreHole.dwg (92.8 KB)


  1. Can anyone advise what file format Rhino is most reliable at importing from? Here are the formats that we can choose from (The Forge export options Aug 2020):
    I’d like to caveat the question a little further: We are trying to avoid mesh formats such as OBJ as meshes result in faceted geometry and we want precision as our app is an engineering/manufacturing application rather than gaming.

  2. Can anyone suggest a better way of converting (on the fly) Inventor ipt geometry to Rhino geometry?

I tag the following people to this question because you seemed to have detailed knowledge in this area when you have helped with similar issues: @dale , @chuck, @kike

When I run _Audit on the dwg, I don’t see any geometry in the file:

Document Manifest:
  Texture Mapping: 0 active, 1 system.
  Material: 0 active, 2 system.
  Line Pattern: 39 active, 3 system.
  Layer: 1 active, 1 system.
  Group: none.
  TextStyle: none.
  Annotation Style: 1 active, 12 system.
  Light: none.
  Hatch Pattern: 0 active, 9 system.
  Block: none.
  Model Geometry: none.
  Total: 41 model components. 28 system components.
  Audit Summary:
    Table tally:
      1 layers
      1 annotation styles
      0 fonts
      39 linetypes
    Object tally:
      0 normal objects
      0 locked objects
      0 hidden objects
      0 deleted objects (in undo buffer)
      0 block definition objects 
      0 reference normal objects
      0 reference locked objects
      0 reference hidden objects
      0 reference block definition objects 
    No errors.

When I run _Audit on the dwg, I don’t see any geometry in the file

That’s interesting. If I open the same file in AutoCAD 2020 here it is:

According to this link latest Rhino can import Autocad dwg 2018 file format which is what we are creating (DWG 2018 AC1032).

That said I’ll export to earlier formats and see if Rhino has any better success.
Have exported the same file to DWG in the following formats:
Made no difference - Rhino always sees zero geometry objects in the file.

STEP is always a good choice when coming from a solids modeler.

A little surprising, being that tools to read and write Rhino’s file format have been open source for ~20 years.

– Dale

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