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Angle based unwrapping thin triangles gives warped results
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Description

System Information
Windows 10 64 bit, GTX 1080Ti and GTX 660Ti

Blender Version
Broken: (2.79b )

Short description of error
Flat areas with thin triangles often look warped when unwrapped using the angle based method, even though the problematic edges have no angle.

Exact steps for others to reproduce the error

  1. Create a mesh with multiple long, thin triangles that are completely flat (common case is triangulating a concave n-gon with rounded corners)
  2. Place seams all around the flat area
  3. Unwrap using the angle based method

Angle Based:

Conformal:

File:

Details

Type
Bug

Event Timeline

Bastien Montagne (mont29) triaged this task as Normal priority.

Not sure there is any bug here, not all UV unwrapping methods work well for all kind of geometry… Could be mere floating point precision limitations, etc. @Campbell Barton (campbellbarton) or @Brecht Van Lommel (brecht) may know better here?

It's a known limitation of the ABF method unfortunately. We can try to invent some new algorithms to solve this, but it's beyond the scope of a bug.