Error in RhinoCommon Unroller vs _UnrollSrf

[Toni_Osterlund (Toni Österlund)]

Hi,
I found a big difference in the results between the RhinoCommon unroller versus the Rhino command _UnrollSrf. Unfortunately found this out after fabrication - and as a notification for future generations I’m posting here my findings.

This subject has been dealt here as well:

RhinoCommon UnrollSurface differs from UnrollSrf command

Have a look at the file in attachment. When I use the UnrollSrf command I get a flat polysurface with smooth edges. When I use RhinoCommons UnrollSurface I get a surface with ugly jaggered edges. How can I achieve the result from the UnrollSrf command using Rhinocommon? [image] For repeating the problem, try this code using Python: import rhinoscriptsyntax as rs obj = rs.GetObject() rs.UnrollSurface(obj) 211214 UnrollSrf vs sr.UnrollSurface.3dm (116.0 KB)

In the background the Rhino’s UnrollSrf seems to shrink faces before unrolling. @dale
The RhinoCommon version does not. This is apparent if you script the command yourself - or if you use OpenNest’s “Unroll” or LunchBox’s “Unroll Brep” components.
Could the shrinkfaces be added to these components in future updates? @Petras_Vestartas @Nathan_Miller

Interestingly FabTool’s “Unroll” component produces correct results, but I suspect it’s based on Rhino command, as it propably predates RhinoCommon.

Here is an example of an “bad” geometry being unrolled before and after shrinking.
Red is the correct outline.

The breps need to be shrunk prior unrolling either in Rhino or in Gh.
In Rhino it’s _ShrinkTrimmedSrf, or in Gh with a small python script, for instance:

[x input type hint: brep]

x.Faces.ShrinkFaces()
a=x

UnrollTests.gh (151.9 KB)

[Petras_Vestartas]

Good to know this!

Would it be any case where doing this to the brep:

x.Faces.ShrinkFaces()

Would actually have worse results?
Or it is the way to do it?

[Toni_Osterlund (Toni Österlund)]

@Petras_Vestartas
This post, and everything in it by @dale provides more insight.

RhinoCommon UnrollSurface differs from UnrollSrf command

Have a look at the file in attachment. When I use the UnrollSrf command I get a flat polysurface with smooth edges. When I use RhinoCommons UnrollSurface I get a surface with ugly jaggered edges. How can I achieve the result from the UnrollSrf command using Rhinocommon? [image] For repeating the problem, try this code using Python: import rhinoscriptsyntax as rs obj = rs.GetObject() rs.UnrollSurface(obj) 211214 UnrollSrf vs sr.UnrollSurface.3dm (116.0 KB)

I’m unfamiliar what brep.Compact() does, but it seems that Dale rebuilds edges, shrinks surfaces and culls unused faces, (plus some checkups) prior.