Decimate Planar generates concave edges #44780

New Issue

Mikhail Rachinskiy · 2015-05-20T01:48:59+02:00

Mikhail Rachinskiy commented

2015-05-20 01:48:59 +02:00

System Information
Windows 8.1 x64
Renderer: GeForce GTX 860M/PCIe/SSE2

Blender Version
Broken: 2.74.5 05c4c24

Short description of error
Decimate modifier generates concave edges with certain geometry while in Planar mode.

Exact steps for others to reproduce the error

Open blend file decimate_planar.blend
Enable Decimate modifier:
- on the most left object (hard edges) → no concave edges
- on the center object (smooth edges) → concave edges, very nasty

on the most right object (more smooth edges) → concave edges, but no intersections (so technically model is fine)

Use case for this is jewelry design, it's better to optimize your models before boolean operations, and it is always appreciated to keep your STL file size small as possible to send them by email.

Here is simple GIF animation to illustrate the issue:

Note: I cannot use Collapse mode, because it generates artifacts that are impossible to fix.

**System Information** Windows 8.1 x64 Renderer: GeForce GTX 860M/PCIe/SSE2 **Blender Version** Broken: 2.74.5 05c4c24 **Short description of error** Decimate modifier generates concave edges with certain geometry while in Planar mode. **Exact steps for others to reproduce the error** - Open blend file [decimate_planar.blend](https://archive.blender.org/developer/F177716/decimate_planar.blend) - Enable Decimate modifier: - on the most left object (hard edges) → no concave edges - on the center object (smooth edges) → concave edges, very nasty ## on the most right object (more smooth edges) → concave edges, but no intersections (so technically model is fine) Use case for this is jewelry design, it's better to optimize your models before boolean operations, and it is always appreciated to keep your STL file size small as possible to send them by email. Here is simple GIF animation to illustrate the issue: ![dcm_cnc.gif](https://archive.blender.org/developer/F177719/dcm_cnc.gif) Note: I cannot use Collapse mode, because it generates artifacts that are impossible to fix. ![dcm_clps.png](https://archive.blender.org/developer/F177722/dcm_clps.png)

Mikhail Rachinskiy commented

2015-05-20 01:48:59 +02:00

Changed status to: 'Open'

Mikhail Rachinskiy commented

2015-05-20 01:48:59 +02:00

Added subscriber: @MikhailRachinskiy

perfection cat commented

2015-05-20 03:05:58 +02:00

Added subscriber: @sindra1961

perfection cat commented

2015-05-20 03:05:58 +02:00

I do not know whether it is helpful for you, but there is such a method.
If you set some seam, it may be improved.
{F177730}

I do not know whether it is helpful for you, but there is such a method. If you set some seam, it may be improved. {[F177730](https://archive.blender.org/developer/F177730/Ex2.png)}![Ex1.png](https://archive.blender.org/developer/F177732/Ex1.png)

Mikhail Rachinskiy commented

2015-05-20 03:33:19 +02:00

Yes I know I can escape concave edges by manualy mark seam/sharp edges, and in this case where I provided example scene as simple is it could possibly be—it looks like an OK solition. But production models are much more difficult than this, and sometimes I have to deal with STL models where it is impossible to select edge loops because it's all triangulated by format standard.

Yes I know I can escape concave edges by **manualy** mark seam/sharp edges, and in this case where I provided example scene as simple is it could possibly be—it looks like an OK solition. But production models are much more difficult than this, and sometimes I have to deal with STL models where it is **impossible** to select edge loops because it's all triangulated by format standard.

Campbell Barton commented

2015-05-20 16:23:26 +02:00

Added subscriber: @ideasman42

Campbell Barton commented

2015-05-20 16:23:26 +02:00

float precision is causing problems here, using double precision for quadric operations makes the example work as expected.

However this is just not going to be well supported (even with doubles, it may be possible to get a more extreme case to fail).

The problem is there are so many faces and they are so small, forming a near flat surface.
Because they are so small, the difference around some parts of the model is detected as zero.

Subdividing a mesh to make a near flat surface then applying decimate, is a rather contrived example. (fine for report of course).

@MikhailRachinskiy, Could you show a practical example which causes this problem?

Edge collapsing is likely to cause some artifacts, In the cases you use it, its possible you'd be better off with re-meshing algorithm rather then decimation.
Or make decimation topology aware, to give better results (which is a much bigger change).

While checking on this report exposed some other issues.
24e1d7f4f4
b5bf5b36f1

With these changes, the test file looks better then it did before, but the artifacts pointed out are still noticeable.

float precision is causing problems here, using double precision for quadric operations makes the example work as expected. However this is just not going to be well supported (even with doubles, it may be possible to get a more extreme case to fail). The problem is there are so many faces and they are so small, forming a near flat surface. Because they are so small, the difference around some parts of the model is detected as zero. Subdividing a mesh to make a near flat surface then applying decimate, is a rather contrived example. (fine for report of course). @MikhailRachinskiy, Could you show a practical example which causes this problem? Edge collapsing is likely to cause *some* artifacts, In the cases you use it, its possible you'd be better off with re-meshing algorithm rather then decimation. Or make decimation topology aware, to give better results *(which is a much bigger change)*. ---- While checking on this report exposed some other issues. 24e1d7f4f4 b5bf5b36f1 With these changes, the test file looks better then it did before, but the artifacts pointed out are still noticeable.

Mikhail Rachinskiy commented

2015-05-21 09:59:27 +02:00

Subdividing a mesh to make a near flat surface then applying decimate, is a rather contrived example.

You have no idea:
http://www.bulgari.com/en-ch/products.html?product_detail_one=228&root_level=315&sign=18
http://www.bulgari.com/en-ch/products.html?product_detail_one=228&root_level=315&sign=21
http://www.bulgari.com/en-ch/products.html?product_detail_one=228&root_level=315&sign=48
http://www.korloff.fr/en/Jewelry/St-Petersbourg
http://www.korloff.fr/en/Jewelry/Yasmine
http://www.carreraycarrera.com/en/collections-en/baile-de-mariposas-collection
http://www.cartier.com/collections/jewelry/collections/trinity-de-cartier
…you got the point :)

Simple example I've provided actually represents the problem of triangle reduction of jewelry ring quite well.
But here are two production examples:

Part of the trinket: trinket.blend
Part of the not bulgari earring: notbulgari_earring.blend

I can understand why there are issues with trinket part on the flat surface with little spheres carved out (but if you could fix it by adding another delimiter to the modifier—that would be just wonderful), but on the bottom of that part you can see exactly the problem I illustrated with the example file, the same thing with not bulgari earring part (note: it may take a while to perform reduction in this case).

Thanks for the fixes! I haven't been able to test them yet tho.

>Subdividing a mesh to make a near flat surface then applying decimate, is a rather contrived example. You have no idea: http://www.bulgari.com/en-ch/products.html?product_detail_one=228&root_level=315&sign=18 http://www.bulgari.com/en-ch/products.html?product_detail_one=228&root_level=315&sign=21 http://www.bulgari.com/en-ch/products.html?product_detail_one=228&root_level=315&sign=48 http://www.korloff.fr/en/Jewelry/St-Petersbourg http://www.korloff.fr/en/Jewelry/Yasmine http://www.carreraycarrera.com/en/collections-en/baile-de-mariposas-collection http://www.cartier.com/collections/jewelry/collections/trinity-de-cartier …you got the point :) Simple example I've provided actually represents the problem of triangle reduction of jewelry ring quite well. But here are two production examples: - Part of the trinket: [trinket.blend](https://archive.blender.org/developer/F178305/trinket.blend) - Part of the not bulgari earring: [notbulgari_earring.blend](https://archive.blender.org/developer/F178306/notbulgari_earring.blend) I can understand why there are issues with trinket part on the flat surface with little spheres carved out (but if you could fix it by adding another delimiter to the modifier—that would be just wonderful), but on the bottom of that part you can see exactly the problem I illustrated with the example file, the same thing with not bulgari earring part (note: it may take a while to perform reduction in this case). Thanks for the fixes! I haven't been able to test them yet tho.

Mikhail Rachinskiy commented

2015-05-21 10:08:03 +02:00

Edge collapsing is likely to cause some artifacts, In the cases you use it, its possible you'd be better off with re-meshing algorithm rather then decimation.

Well, if you brought that up yourself :) #39748

>Edge collapsing is likely to cause some artifacts, In the cases you use it, its possible you'd be better off with re-meshing algorithm rather then decimation. Well, if you brought that up yourself :) #39748

Campbell Barton commented

2015-05-21 10:28:57 +02:00

Changed status from 'Open' to: 'Resolved'

Campbell Barton closed this issue

2015-05-21 10:28:57 +02:00

Campbell Barton self-assigned this 2015-05-21 10:28:57 +02:00

Campbell Barton commented

2015-05-21 10:28:57 +02:00

@MikhailRachinskiy, I can see you're looking for the best solution here.
But from what I can tell Blender simply doesn't have a good way to remesh at the moment (at the quality level you're looking at).

Thats not really a bug, its just a limit in the software. It would be good to rewrite or add improved methods to the existing remesh modifier.

I looked into further improvements and made some reasonable progress for your example.

aa54d93a29

See Example images:

I managed to get it so none of the edges collapsed around the edges of the mesh (as stated in this report). But the other geometry has such bad topology that I prefer not to commit it.

Closing this report, while its not fixed strictly speaking, this case isn't really ideal for decimate modifier, and it works a lot better now then it did before.

@MikhailRachinskiy, I can see you're looking for the best solution here. But from what I can tell Blender simply doesn't have a good way to remesh at the moment (at the quality level you're looking at). Thats not really a bug, its just a limit in the software. It would be good to rewrite or add improved methods to the existing remesh modifier. I looked into further improvements and made some reasonable progress for your example. aa54d93a29 See Example images: ![248_decimate_topology_01.png](https://archive.blender.org/developer/F178310/248_decimate_topology_01.png) ![248_decimate_topology_02.png](https://archive.blender.org/developer/F178308/248_decimate_topology_02.png) I managed to get it so none of the edges collapsed around the edges of the mesh (as stated in this report). But the other geometry has such bad topology that I prefer not to commit it. ---- Closing this report, while its not fixed *strictly speaking*, this case isn't really ideal for decimate modifier, and it works a lot better now then it did before.

Mikhail Rachinskiy commented

2015-05-21 11:05:08 +02:00

Collapse decimation looks really beautiful now.
Big thanks for what you've done, it will spare me (and not only me) if not from all, but at least from part of the issues with decimation.

Collapse decimation looks really beautiful now. Big thanks for what you've done, it will spare me (and not only me) if not from all, but at least from part of the issues with decimation.

Campbell Barton commented

2015-05-21 11:47:18 +02:00

Changed status from 'Resolved' to: 'Open'

Campbell Barton reopened this issue

2015-05-21 11:47:18 +02:00

Campbell Barton commented

2015-05-21 11:47:18 +02:00

Checking further, notbulgari_earring.blend, it looks like we will need to use double precision.

See comparison: (current master, left, current master /w double precision quadric's, right).

Checking further, `notbulgari_earring.blend`, it looks like we will need to use double precision. See comparison: (current master, left, current master /w double precision quadric's, right). ![out_ring_alm.png](https://archive.blender.org/developer/F178318/out_ring_alm.png)

Mikhail Rachinskiy commented

2015-05-21 12:29:07 +02:00

WOW! This is the result I was looking for!

blender-admin commented

2015-05-21 13:06:30 +02:00

This issue was referenced by e37c4e5819

This issue was referenced by e37c4e5819aec1f853fdd71cf60004aa2363f7d9

Campbell Barton commented

2015-05-21 13:11:07 +02:00

Changed status from 'Open' to: 'Resolved'

Campbell Barton closed this issue

2015-05-21 13:11:07 +02:00

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Decimate Planar generates concave edges #44780

on the most right object (more smooth edges) → concave edges, but no intersections (so technically model is fine)