Invisible matte object (well sort-of)

[rmaytee]

I'm wondering if anyone know how I can achieve this.

I am hoping to animate a space developing from the ground-up. I thought i would be able to place a large box over the space that was invisible. The box could mask everything it over-laps, but as the box is moved up, you could see everything beneath it. The problem is, I want to see this happen from a view above the space, similar to the second image.

The images below are obviously not the actual model, I just wanted to create some test. But I can't seem to make the box mask the objects it covers (physically), but still allow the camera to see the objects it is not physically covering. Obviously, once an objects has a matte/mask property, if it blocks the view of things behind it, they will be masked.

Does this make sense at all?

I guess another way to describe it would be like animated clipping planes. But only, the clip will be done on the scene's Z-axis, not the camera's.

Any ideas?

[instinct]

Well this wont be that easy unless you use solids heh. You could try with the slice modifier and a cap modifier. this will most likely go bonkers wth more complex meshes tho.

Regards,
Thorsten

[Mikokariadis]

You could do something like that in post, making a mask with two separate plates, the one with the foreground wich is to be "revealed" by the mask that is feeding on the background plate. Though that could start to look funky if you want to make it look in perspective.

For doing that in 3d we went for scalpelmax 2010 and it has no problem handling big complex models.

[rmaytee]

Instinct was right on. Slice modifier is easy, and does just what I need it to do.

Not sure if it will work on proxies. Haven't tried that yet, but we'll see.

[rmaytee]

Looks like it doesn't work with proxies, but for this project, I can just use the actual models.