Unfold Surface giving strange results on trimmed NURBS cylinder

[Juliensv]

Hello, I have a NURBS surface which is made from a half-cylinder and then trimmed. I use the Unfold surface command but the shape it spit out is a little strange. One side seems correct, but the other side has kind af a bulbous shape which does not correspond to the NURBS surface at all! The strange thing is that when I reversed the surface normal, the unfolded shape created looks correct.

This is in VW2023 SP3

I have included both results in the file as well as the two shapes super-imposed.

 

Any idea why the command is behaving this way? Is it a bug or something I did?

 

Unfold surface troubleshooting.vwx

Edited February 3, 2023 by Juliensv

[Pat Stanford]

I can't tell from your screen shots, but is your NURBS curved in multiple directions? If so, I don't think VW will be able to unfold it as the built in command can only unfold "Developable" surfaces. Think something that can be created from a piece of paper without any distortions.  So a straight "tunnel" could be unfolded, but a curved tunnel can not.

 

HTH

[Juliensv]

Hi Pat,

 

The NURBS surface is just a slice from a cylinder, so I believe it should be "developable". I think really what I'm confused about is why it would behave differently with a reversed surface normal.

[Pat Stanford]

There was a thread several years ago about Unfold not working on Trimmed NURBS. Or at least some Trimmed NURBS.  Never saw a real solution. I think the Unfold may not be powerful enough to handle your case.

 

Hopefully somebody who know will be able to answer your question.

[Claes Lundstrom]

Looks like a bug to me, even though I never use VW for my unfolds. The only way to extract a predictable seems to be to extract two edge curves and then loft them into a new surface. 

[Kevin McAllister]

I would encourage you to submit it as a bug. The only way the tool will get better is if someone looks at it.

I have had accuracy issues with unwrapped surfaces in the past and tend to use Rhino now and export back to Vectorworks. Accuracy is important 🙂

 

Kevin