ambient occlusion artifact

Hey everyone.

So I’m having some trouble with ambient occlusion in blender. This very same thing happened to me last project but I thought it was just a fluke.

Look at the corner. that column is all black and grainy! Notice how the other side doesn’t have it. That’s how it should look (their the same material and apart of the same mesh). Also there’s a black seem where my object is mirrored from the AO. Non of my other mirrored objects have that problem. I’m more concerned about that boxy column on the corner though.

The normals are not reversed, their facing outside correctly. Does anyone else get this? Could someone please tell me what that’s from?

Thanks so much.

The problem is in the geometry just delete it and recreate it, it’s only a box.

Try using all ray traced lights first to see if it goes away. Your problem looks similar to mine when I used buffered shading spot lights. In order to get the buffered spot lights to work, I had to adjust the clipping range to be close to the building.

Hmmm… To me, it looks like what happens when you have two faces sharing the same position. Blender tends to freak out a bit when that happens.

This is with the mirror-modifier, correct? Have you tried Applying the modifier and seeing if the problem persists? If you apply the modifier, and then remove doubles, are any vertices removed?

thankyou guys! spectre-7 SUCCESS!!! For some reason i had two boxes in precisely the same position. That’s what it was. I know its just a box and could have put a new one but then if it happened on more complex geometry i’d like to know how to fix it without rebuilding.

Glad to help… and yeah, it’s a more common problem than you might expect. It’s definitely a good thing to have a handle on, but luckily also easy to fix. :slight_smile:

I also had a problem that yielded similar symptoms like that, but it was for normal map baking, and wasn’t because of overlapping faces or shared UV space. What caused that was a polygon that, in the UV coordinates, occupied a total area very close to 0. In other words, it was a very thin polygon, and the normal map of adjacent polygons were solid grey because of it.