IGS-Export: Keep a trimmed surface as a trimmed surface

I would like to export some surfaces from a rhino model (which I did not create) in order to use them in a third party programme (NAPA, https://www.napa.fi/). The surfaces are trimmed surfaces. I have the problem that only the untrimmed surface is displayed in NAPA after the export.
You can activate the object control points of the trimmed surface in Rhino and then you can see very quickly what the original surface looked like. Is there any way to define this surface in such a way that the “original” object control points are deleted and recreated on the basis of the trimmed surface? Or is there a setting in the export to export only the trimmed surface information?

In NAPA I can only reference on a closed surface. If various surfaces are suddenly untrimmed, I have a lot of open edges that make life difficult for me.

Before exporting I had already tried to use the ShrinkTrimmedSurface-command. Unfortunately, it doesn’t work with the surface - only some control points have moved a little, but nothing else happened.

Hi Alexandros -

When you export a trimmed surface from Rhino in the IGES format and then import that again, you will see that the surface is trimmed. That means that the trimming information is written to the IGES file. What other applications do with that information is beyond our control.

  • When a straight trim is on an isocurve, you can use ShrinkTrimmedSrf to move the control points to the trimmed edge
  • When a straight trim is not on an isocurve, you should be able to use RefitTrim to recreate a surface that follows that trimmed edge
  • When the trim curve is not straight, and depending on the situation, you might be able to duplicate the edge, explode it, and if that results in 4 or less curves, use EdgeSrf


Hi Wim,

as I work in the superyacht business you can imagine that nearly every trim curve is not straight. I found another workaround which helped me to transfer the surfaces from Rhino to NAPA.

I had a conversation with the support of NAPA and they told me that NAPA is only able to work with entities 128 and/or 144. All curves, points and surfaces need to have a maximum degree of 3.
So I used the possibility to create my own “export type” in Rhino. I defined the IGES-type details for the points and curves and also for the surfaces as mentioned above. And then it runs!

It was just a problem with the export settings. Now I can see the trimmed surfaces in NAPA and I can reference on them, describe rooms, calculate them and so on.

Thank you for your fast response!

Best regards,


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