Angle based UV-unwrap: distorted UV island with even angles on geometry #78101

New Issue

Vyacheslav Kobozev · 2020-06-21T17:05:58+02:00

2020-06-21 17:05:58 +02:00

System Information
Operating system: Windows-7-6.1.7601-SP1 64 Bits
Graphics card: GeForce GT 640/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 445.87

Blender Version
Broken: version: 2.90.0 Alpha, branch: master, commit date: 2020-06-19 23:28, hash: 874af5301c

Short description of error

Exact steps for others to reproduce the error
2020-06-21_18-02-13.mp4
untitled.blend

**System Information** Operating system: Windows-7-6.1.7601-SP1 64 Bits Graphics card: GeForce GT 640/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 445.87 **Blender Version** Broken: version: 2.90.0 Alpha, branch: master, commit date: 2020-06-19 23:28, hash: `874af5301c` **Short description of error** ![42431604.png](https://archive.blender.org/developer/F8635251/42431604.png) **Exact steps for others to reproduce the error** [2020-06-21_18-02-13.mp4](https://archive.blender.org/developer/F8635253/2020-06-21_18-02-13.mp4) [untitled.blend](https://archive.blender.org/developer/F8635255/untitled.blend)

Vyacheslav Kobozev commented

2020-06-21 17:05:58 +02:00

Added subscriber: @Vyach

blender-admin commented

2020-06-21 17:05:58 +02:00

#102833 was marked as duplicate of this issue

Germano Cavalcante commented

2020-06-23 23:08:18 +02:00

Added subscriber: @mano-wii

Germano Cavalcante commented

2020-06-23 23:08:18 +02:00

Changed status from 'Needs Triage' to: 'Confirmed'

Germano Cavalcante commented

2020-06-23 23:08:18 +02:00

Perhaps it is a known problem since we have: #71959 (Improve UV unwrapping balance between angle and area preservation)
But I'm confirming for now.

Perhaps it is a known problem since we have: #71959 (Improve UV unwrapping balance between angle and area preservation) But I'm confirming for now.

Vyacheslav Kobozev commented

2020-06-24 00:36:14 +02:00

@mano-wii
okay

@mano-wii okay

MB commented

2020-10-08 18:15:27 +02:00

Added subscriber: @no4me

Richard Antalik commented

2020-11-24 20:30:15 +01:00

Added subscriber: @iss

Richard Antalik commented

2020-11-24 20:30:15 +01:00

Adding back modelling because this is otherwise untagged with project in https://developer.blender.org/maniphest/query/J_RaaSzk5wr0/

Vyacheslav Kobozev commented

2021-01-27 03:26:54 +01:00

poke

Paul Kotelevets commented

2021-08-27 11:00:26 +02:00

Added subscriber: @1D_Inc

Paul Kotelevets commented

2021-08-27 11:00:27 +02:00

I am not sure that angle-based term stands for "preserving all the angles".
I think it works different.

I am not sure that angle-based term stands for "preserving all the angles". I think it works different.

Vyacheslav Kobozev commented

2021-08-27 16:15:24 +02:00

In #78101#1212397, @1D_Inc wrote:
I am not sure that angle-based term stands for "preserving all the angles".
I think it works different.

There shouldn`t be different behavior for similar angles, because it become unpredictable (what angle will be distorted?)

> In #78101#1212397, @1D_Inc wrote: > I am not sure that angle-based term stands for "preserving all the angles". > I think it works different. There shouldn`t be different behavior for similar angles, because it become unpredictable (what angle will be distorted?)

Paul Kotelevets commented

2021-08-27 23:46:40 +02:00

In #78101#1212518, @Vyach wrote:

There shouldn`t be different behavior for similar angles, because it become unpredictable (what angle will be distorted?)

Angle based method is supposed to deal with organic/irregular topology, while conformal - with linear. Maybe it is a naming problem.

> In #78101#1212518, @Vyach wrote: > There shouldn`t be different behavior for similar angles, because it become unpredictable (what angle will be distorted?) Angle based method is supposed to deal with organic/irregular topology, while conformal - with linear. Maybe it is a naming problem. ![image.png](https://archive.blender.org/developer/F10337988/image.png) ![image.png](https://archive.blender.org/developer/F10337990/image.png)

Chris Blackbourn commented

2022-05-07 04:45:09 +02:00

Added subscriber: @Chris_Blackbourn

Chris Blackbourn commented

2022-05-07 04:45:09 +02:00

I actually spotted this one in the code first, so it's nice to have a real world example.

I think what's happening here is those quads are being triangulated before being passed to the solver. By triangulating, we create additional constraints across the diagonals not present in the original mesh.

I've constructed a fully symmetric model which is specially designed to demonstrate the problem here:

Note that a fully symmetric unwrap can be created by hand, keeping that square a square, and something like this would be the desired unwrapping:

Blender file for the curious. You can try scaling in the 'Y' for some interesting results, splitting the quad, or removing some of the triangles. UnlikelyShape.blend

In terms of fixes, if this is the cause of the bug, we would need to upgrade the LSCM solver to operate directly on quads as well as triangles.

I just skimmed through the original "Least Squares Conformal Maps
for Automatic Texture Atlas Generation" paper and it doesn't mention quads, so this would be either a literature search or some original research or perhaps a "contact-the-author" situation.

I actually spotted this one in the code first, so it's nice to have a real world example. I think what's happening here is those quads are being triangulated before being passed to the solver. By triangulating, we create additional constraints across the diagonals not present in the original mesh. I've constructed a fully symmetric model which is specially designed to demonstrate the problem here: ![image.png](https://archive.blender.org/developer/F13055616/image.png) Note that a fully symmetric unwrap can be created by hand, keeping that square a square, and something like this would be the desired unwrapping: ![image.png](https://archive.blender.org/developer/F13055633/image.png) Blender file for the curious. You can try scaling in the 'Y' for some interesting results, splitting the quad, or removing some of the triangles. [UnlikelyShape.blend](https://archive.blender.org/developer/F13055620/UnlikelyShape.blend) In terms of fixes, if this is the cause of the bug, we would need to upgrade the LSCM solver to operate directly on quads as well as triangles. I just skimmed through the original "Least Squares Conformal Maps for Automatic Texture Atlas Generation" paper and it doesn't mention quads, so this would be either a literature search or some original research or perhaps a "contact-the-author" situation.

Paul Kotelevets commented

2022-05-07 07:50:35 +02:00

@Chris_Blackbourn interesting case.
In 2.7 angle based method give a better result with such kind of a geometry (at least tries to), while in 3.0 both methods give the same results.

@Chris_Blackbourn interesting case. In 2.7 angle based method give a better result with such kind of a geometry (at least tries to), while in 3.0 both methods give the same results. ![image.png](https://archive.blender.org/developer/F13055895/image.png)

Chris Blackbourn self-assigned this 2022-11-13 01:00:53 +01:00

Chris Blackbourn commented

2022-11-13 01:00:53 +01:00

Turns out to be more subtle than anticipated. Please contact me if you're working on this one.

Chris Blackbourn commented

2022-11-30 04:52:31 +01:00

See another instance of the bug here: https://developer.blender.org/T102833

Germano Cavalcante commented

2022-11-30 15:25:33 +01:00

Added subscriber: @070NRG

Philipp Oeser removed the

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Angle based UV-unwrap: distorted UV island with even angles on geometry #78101