"banding" in maya renders

[mr-mint123]

I'm almost ready to throw my monitor out the window here. I tend to use a dome lighting setup with spots to simulate a radiosity type look. But sometimes, for no apparent reason, I get shadow banding on surfaces that are close to one another. For instance, if two planes are on top of one another, the one toward the camera gets shadow stripes across its surface. I've gotten it to work using lo-res dmaps (256) and the filter setting at 2, but like I said, sometimes it just refuses to cooperate. I set up lights using similar settings to these earlier today and it worked fine. I had a crash and lost the last save with the working light setup. I went back in and set up the lights the same way as before and BOOM! I get bands. What's going on? I've looked through the documentation, nothing I've found there helps at all, any clues?

[gmask]

How many lights do you have in the dome.. 256 seem high for this use. I have done this with dozens of lights and dmap res of 64 and never comes across this problem.

[mr-mint123]

It's a half dome really (only one side of the model needs to be visible). There's probably only about 10 lights in all (including a primary light source). But I have this problem with only one spot lit up, too. Point lights AND directionals will do it as well. Not all the time, though, every once and awhile a light setup will work. For the most part I just get these "shadow bands" running across the model. No rhyme or reason to it.

I tried turning off Dmap auto exposure for the lights (as I think the maya docs suggest) but no go. I've had this problem since I started using maya (2 years ago) and no one else I know can replicate or explain it (it's come up on different systems with different hardware, so I know it's not a system thing).

[gmask]

if you want mail me the file info@gmask.com or post an image..

[summers3d]

Have you tried adjusting your dmap bias? I've had to do this from time to time to take care of banding problems. Dmap bias adjusts the positon either closer or farther from the shadow casting light source...
-David

[mr-mint123]

I have messed around with the dmap bias, it generally cans all my shadows and things look like they're lit with an ambient. Even with the smallest adjustment it does this.