Is it possible to Z combine OpenEXRs with volumetrics that are in the active render layer?


I have a rather large scene, and I planned to break it up by rendering only portions of it at once into OpenEXRs with a depth pass, and later Z combining them in the compositor. Unfortunately, I happen to have volumetric materials in my scene, and other objects pass through that volume. And the way my scene is, and due to my computer specs, I simply cannot render the volumetric object, and the objects passing through it all at the same time.

So I’ve read that it is not possible to capture the Z depth of a volumetric material, which makes sense, there can only be one depth value per pixel, and a volumetric material would require many more (or at leas that’s how I understood it).

But the way I understand how all this works, it should be possible to combine an OpenEXR with a volumetric materail that is in the active render layer, because the volume is still inside Blender in 3 dimensions, so it should be able to sort of position that OpenEXR inside that volume. Shouldn’t it? But I can’t get it to work. Using the Z combine node, it only puts the openEXR on top of the render layer, just as if they were combined with an alpha over node.

If you know a solution to this, or if there’s even one, please let me know.