Coplanar face and GI Problem

[danb4026]

I have attached an image that exemplifies the problem I am trying to solve.

Many times, I will create a ceiling plane that I will make invisible to the camera. I do this when creating a plan view of a space with the camera pointing down. This allows me have the ceiling for interior spaces GI calculations, but not be seen by the camera.

 

The problem, as shown below, is when the ceiling sits right on top of walls, columns, etc. I end up with the dark, shadowing, and/or distortion on the faces directly below the ceiling. The box on the left has the same ceiling on top of it as the box on the right, just not visible to the camera.

 

If I make the ceiling not cast shadows, that defeats the whole purpose of using it for GI.

 

Is there a remedy for this?

[WAcky]

cut holes in the ceiling where it joins the columns?

[danb4026]

Hey James, I do that when there isn't much to cut. Sometimes I will even boolean the ceiling.

 

I have a situation where I have already built the space which has tons of mullions and lots more geometry running right up to the ceiling. I would hate to have to cut holes for everything and when I boolean it, it becomes a mess.

[WAcky]

Which renderer are you using?

[danb4026]

Vray

[WAcky]

The only thing I can think of is to try setting your secondary rays bias from 0.0 to 0.01 in the global switches rollout.

 

Other than that the only thing I can suggest is to make the the tops of the columns a seperate item and make them not receive shadows or cut holes into the ceiling...

[BrianKitts]

when I do renders like this I render out a mask to use in post to poche the tops of the walls.

 

Just take a plane with it's matte set to -1 and place it just barely below the tops of the walls. render it out to create a layer in PS, color overlay and stroke it as you wish.

 

another way to do it would be to just detach the top faces of your walls, assign its own material so that you could isolate the top with a multi-matte render element. hmmmmm, now that I think about it, that's how I'll probably do it in the future.

Edited March 23, 2010 by BrianKitts

[Jose Negrete]

if you are rendering an ortho top view you can use the camera's clipping planes feature. to avoid the transparent ceiling setup.