Major problem(s) with decimation. Asking for help/advice...

Support Modeling
1

Hi BA,
I’m really having problems with the decimation modifier. I have large triangular meshes that I need to decimate (often >3M tris).
The problem is that some regions are ‘over-decimated’ while others don’t hardly decimate at all. I know this is because of the underlying geometry/topology, but I can’t find any solution. Even if I only decimate by 0.9, or 0.95 I get really poor results.

See pictures below.
This is really critical to my work so if there’s any advice or suggestions thank you very much.

Note that I’ve been using Meshlab lately to decimate with some success but results are not very good either and it is very tedious to export and reimport multiple objects just to decimate… I really need to keep it in Blender for scripting purposes.

Before decimation:

before decimation.JPG1503×918 302 KB

After 0.9 decimation (very badly shaped tris). I’ve tried relaxing to improve but the tris are too distorted.

after 09 decimation horrible.JPG1589×903 300 KB

Again, any help much appreciated.

2

Looking at your 1st screenshot it looks like it was originally all quads and got triangulated for some reason.
So try this :

  • select all
  • press CTRL+F -> Tri to Quad in the hope the triangles will be nicely enough converted back into the quads they were originally
  • add a Decimate modifier but set it to “Unsubdivide” instead of the default “Collapse” (and why having it all quads is better as unsubdivide would do nothing for triangles)
    Try to see with Iteration to 2 , to 4 and to 6 how it goes
3

Thanks for the reply. I’m trying this concept in a little different way (i’ll share if it works), but the problem is that I’m maxing out memory (i’ve got 6gb). So I guess i’ll have to get another 8 gig and see if it works.