flythrough render pass for comping people & including refractions

[leotchest]

I am in the process of rendering out 3,800 frames for an interior flythrough. Im looking for a good technique for rendering the people (a combination of Populate, RPC's (sad but true) and maybe some animated axyz models if i can find the time).
So the people would be rendered in a separate pass and added to the main flythrough afterwards in Premiere Pro. I'm experimenting with making all the objects in the scene (apart from the people) matte objects (by right clicking and changing the 'vray properties') but my main concern is what happens when there is a glass object in front of one of these people. The mask that i am rendering will completely block the view of the person if there is glass in front of them - thats going to mess up the flythrough of course. The scene is very large with hundreds of materials and countless objects, so i need to be doing this in as simple a manner as possible. Ideally, in addition to being able to render the people with a mask that accounts for the refractions that are needed, i'd like to be able to include a pass for capturing shadows as well as reflections. Ive tried but currently those passes just turn out black. I'm mostly concerned about the refraction problem. Any help would be much appreciated.

[joconnell]

I'd nearly be inclined to do three passes - one for your static scene with no glass at all and cached GI, a second for your people with a shadow pass and a vray dirt pass as an extra tex to make some kind of contact shadows, then a third pass with your people and environment as matte objects and render your glass. You can add over your reflection render, and depending on what type of glass you had in your scene (such as just flat, thin panes) you might not have had much difference in look of an object rendered through a refraction anyway. Refractions will warp and shift objects quite obviously if it's quite thick and there's curvature to it, but if it's very thin and perfectly flat, there might have only been a tiny offset in the difference.

[leotchest]

The scene is well optimised for render efficiency, but even so its taking about 11 days to render on my 7-8 machines. I have sero time available for re-rendering - so i cant re-render without the glass etc (ive considered using an online render farm but the budget is too low to warrant such an expense). For the alphas i am experimenting with setting the glass objects to have an alpha contribution of something like -0.25 and that way i get a sort of view of the people through the glass. I am having some limited success with that at the moment (sometimes it works and other times it doesnt). However, i would like also to be able to capture the reflections - this frame shows there are reflections on the floor - i would like to capture them in a render element when i render the people pass, but cannot seem to get it to work - all i get is "black" in my reflection passes.

[joconnell]

Ah - might it be something like the rpc's not using a vray material so they don't appear in passes?

[leotchest]

Hmmnnnn - that sounds ominous

[joconnell]

Yeah. Vray will only render passes for things that use vray materials, other shaders won't always pass back the information that vray uses for it's buffers so I'd try a simple test first of a scene with a few rpc objects on a plane and add in some passes to see what comes out. If you use the eye dropper in the material editor to load the rpc material into one of the slots, what does it come back as? If you've got the option of something like an rpc texture (I've never used it) then you could load that into a vray light material or the self illumination channel of a vraymtl and you'd get proper passes too.