Date: Mon, 3 Dec 2012 20:35:16 -0700 (MST)
From: "Roland Kahlenberg (RoRK)" <aemaillist@broadcastgems.com>
To: After Effects Mail List <AE-List@media-motion.tv>
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In-Reply-To: <31540381.54674.1354591591980.JavaMail.root@mail5c.brinkster.com>
Subject: Re: [AE] Generate Z-depth pass in AE
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----- Original Message -----
From: "Chris Zwar" <chris@chriszwar.com>
To: "After Effects Mail List" <AE-List@media-motion.tv>
Sent: Tuesday, December 4, 2012 9:27:22 AM
Subject: Re: [AE] Generate Z-depth pass in AE

Particular can obscure particles based on a Z depth map. It can only
obscure 1 3D After Effects layer.

If you have a composition made up of multiple 3D layers then the only
way to get Particular to obscure particles correctly is to use a z depth
map. 
-------------------

For a 'particularized' comp with multiple 3D layers that require obscuration, a more elegant solution is to copy these layers and the camera into another comp. Then nest this comp into the 'particularized' comp. Place it below the Particular Layer, make it a 3D layer, Parent it to the Active Camera and place the following script into the nested comp's position property - 
CamZoomVal = thisComp.activeCamera.cameraOption.zoom;
[0,0,CamZoomVal]

Off course, you would also switch off the nested comp's visibility switch. Then set Particular's obscuration layer to point to this nested comp. The only setback is that manual updates to the layers in the nested comps are required for any changes made to the affected layers in the 'particularized' comp. Expressions can be used to link the layers but unfortunately the live linking via Expressions will slow down AE quite a bit.


HTH
- Roland Kahlenberg
Intensive mocha & AE Training in Singapore and Other Dangerous Locations
Imagineer Systems (mocha) Certified Instructor & Adobe After Effects ACE/ACI (version 7)