Untrim doesn't always produce the underlying NurbsSurface's natural edges

[CADacombs]

This is related to this post: STEP import: Some BrepEdge curves are modified - Autodesk Community - Fusion 360

Open the .stp file in EvaluateMyBrepEdges.zip

Using these scripts (output is printed in Text Commands panel),

https://github.com/CADacombs/fusion360python/blob/main/Inspect_BrepFaceSrf.py

https://github.com/CADacombs/fusion360python/blob/main/Inspect_Crv.py

observe that 2 of the BrepEdges curves are not the natural edges of the NurbsSurface.

I expect that the Untrim command would replace the modified edges with the NurbsSurface's natural edges, but it doesn't.  Please fix this.

Thank you,

Steve

[Phil.E]

Thanks I put in an improvement request for this.

[TrippyLighting]

@CADacombs I think for the time being I will move my surfacing projects to my other CAD software.

Maybe I am overreacting but I admit have a very hard time with this and the other post about the STEP import.

I made a post about this on the Fusion 360 EE Slack Channel.

[TrippyLighting]

@CADacombs I posted both of these issues on the EE Slack Channel and received some feedback:

"Thanks for posting this. For reference FUS-103737 has been opened to investigate this one further. I suspect it will ultimately need to be handled by the ASM team"

That most likely means that this is not going to be a quick fix!

[JamieGilchrist]

@CADacombs ,

I'm curious, the source file came from Rhino, can you share the step file that came from Rhino too?  I'm seeing that it's gone through two systems before getting into Fusion.  FWIW I was able to bring your data into Alias, create 5Degree boundary curves, create surface and iges and step out the data and didn't see the same result as your original step and iges files.  I wonder if there is a translator version on our end our your system that may be causing this.

[CADacombs]

The STEP file was directly made by Rhino of a surface made in Rhino.  Regardless, the attached contains STEP files of degree 2, 4, 5, 6, and 7 Bezier surfaces made in Rhino and exported once.

Referring to the

lower U surface parameter as West,

upper U as East,

lower V as South,

upper V as North,

All West and North edges are degree 3 curves, and the South edge of degree 2 is an Arc3D.  Untrim doesn't change any of them.

All the other edge curves are "natural" to their surfaces.

If you like using my two scripts, here is a combination of them:

https://github.com/CADacombs/fusion360python/blob/main/Inspect_Geom.py