Validity of trim loops

Rhino Developer
1

Hi,

please take a look at the following face inside this 3dm file:
http://downloads.moduleworks.com/public/ProblemSurface.zip

I convert the face into our NLIB-based format by getting the NURBS representation including the 2D U/V trim loops.
In this case, I get a single outer trim loop which consists of 5 edges. When converting this face to NLIB, we see an face that is invalid (smaller).

If I however export this face as a STEP file and re-import it into Rhino, the subsequent conversion to NLIB works correctly. Strangely, there are now 2 trim loops with each 4 edges.

I’m a little confused why the conversion fails with the original NURBS representation.

Thanks
Mark

2

That surface has control points all over. [F10]
If you shrinktrimmedsrf it’s a lot more reasonable.
I know nothing about NLIB, but the shrunk surface is a lot more palatable.
clk

3

Hi Chris,

thanks for the reply.
I’ve tried the shrinktrimmedsrf command, and indeed, I was able to convert the face correctly to NLIB.
I wonder if this command is automatically run when it gets exported via STEP?

Is there an API call (RhinoCommon) to do this programmatically?

Thanks
Mark

4

Changed category to “Rhino Developer”

5

Call ShrinkFaces() on the Faces collection of a Brep.

See http://4.rhino3d.com/5/rhinocommon/html/M_Rhino_Geometry_Collections_BrepFaceList_ShrinkFaces.htm