Decimate Modifier Produces Gaps

I’m applying the decimate modifier to a model, but for some reason, it sometimes leads to visible gaps, like this one:

Before:

After:

As you can see I intentionally selected the vertex that gets broken up to show that it’s not two vertices at the same place or some other anomaly in the mesh.

Does anyone know what makes the Decimate modifier behave like that? Anything I can change about the mesh to prevent it?

Really your screenshots are meaningless. How can anyone interpret what is going on with such an isolated view and no actual blend file to look at. Also supply basic system information and what actual blender version you are using

Why do you think they’re meaningless? They show the corner of a mesh, first perfectly sealed, then with the top blown wide open.

Maybe a little illustration shows it better:

I’m running Blender x64 r52813 (nightly build), that should be shortly before the 2.65 public release, on Windows 8. I cannot provide the .blend file because it is a commercial model, but it has been created in Blender (not imported), fits in a bounding box of about 50 units and contains >600,000 vertices.

I could try to create a reproduction case, but in any case, I think I might have already figured out what was going on: I applied the “Edge Split” modifier before the “Decimate” modifier, so that vertex was actually split into 3 (one with the for each face connected to it with a sharp edge).

It still surprises me very much that “Decimate” moves vertices around (versus only removing and inserting vertices), but knowing that now, I can arrange the modifiers accordingly.

Glad that you got it to work.

Lots of users post images that give out as little information as possible and it’s frustrating sometimes.

I’ll answer that with two images. Try to think what’s wrong with the mesh in the first one, I’ll reveal the answer below the images.

[ATTACH=CONFIG]208712[/ATTACH]

[ATTACH=CONFIG]208713[/ATTACH]

The problem in the first image is that it’s not a mesh, it’s an image I made in GIMP in a few seconds, having 8 color values = meaningless.
Second image is something I posted in another thread as visual for written words. It shows part of a mesh, its topology, modifier that was important for the discussion, arrow highlighting the area that was mentioned so one doesn’t have to discover it, Blender version, and all that with enough resolution so that your eyeball doesn’t have to touch the screen to see anything.

It’s not that hard. Just have to give some thought for the viewer.

Now I’m a little bit hurt.

I did think about the viewers, specifically I provided the first picture with highlighted vertices so they could understand the shape I’m showing and then proceed to the second one seeing what has changed. I also described what I am trying to show (and kept my description as short and focused as possible so nobody would be put off reading several paragraphs of text).

But maybe I was too sunk into my modeling work to notice that unless one looks closely at both images, it’s just a random prism of different grays.

I’ll try to provide clearer illustrations in the future.