Optimizing a very large scene

[busseynova]

I'm putting together a city masterplan visualization, lots going on - Rail clone buildings with light materials, forest pack trees, tyflow people. I'm just using default GI at the moment - LC/BF, all default settings in fact.

beyond the obvious of minimising polycount and texture size, is there any tools with which I can find ways to optimize the lighting?

Would scene units make a difference? I'm working in millimeters, which is probably not ideal from a UI display perspective, but would it effect render times?

[glorybound]

I think V-Ray does most of the heaving lifting for you now.

[busseynova]

One thing that might help is texture baking... I have an uplight on every tree - trees scattered with forest pack. I'm assuming texture baking this light in to the texture could help with computation time?

[Neilg]

One thing that might help is texture baking... I have an uplight on every tree - trees scattered with forest pack. I'm assuming texture baking this light in to the texture could help with computation time?

Not worth the manpower. adaptive lights made a big difference in this area.
Dont have lights inside glass fixtures - make the glass fixtures invisible to gi and not cast shadows. Turn off gi reflective and refractive caustics.
Make sure none of your trees are using translucency - you could turn off trace reflections, keep the specular and keep the 2-sided as they add a lot visually from a distance.

Convert all your textures to hdriloader and tx maps - this is a one click thing via a script included in vray. that turns all your textures into proxies too.

that's about it without any drastic changes. you should be able to push it pretty far.

your system units being in mm might cause you issues. i'd only use that if i was modeling jewelry. i use inches for single buildings and meters for multiple city block scale scenes. mostly you're going to find navigating, zooming panning and working in the file a huge pain in the ass. i never let it go long enough to see if it causes render issues too.

[Oleg_Budeanu]

This may be unpopular opinion, but I am always getting quite nice rendertime reducement when I am using irradiance map instead of BF. Also, it is much cleaner.
If you have moving people / cars you can untick "use irradiance map" in their materials and you'll get BF working only for them.

[^Lele^]

What Neil said.
And you have two more things to play with: proxies and bufferless rendering.
Here's an official guide to lowering RAM usage.

[busseynova]

Dont have lights inside glass fixtures - make the glass fixtures invisible to gi and not cast shadows.

First one isn't an option unfortunately. Glass in multisub material in many cases, but using a vray material wrapper on the glass mat with the GI off will have the same effect won't it?

Turn off gi reflective and refractive caustics.
.

Can this be done globally, or on does it need to be on an object basis?

Thanks, for the tips, I will try the TX conversion.

[busseynova]

Also if I set the Refraction IOR of my glass to 1 it will essentially be like Corona's 'simple' refraction - i.e the rays will not be deviated from their path at all as they pass through a volume with that material...?

[Neilg]

Can this be done globally, or on does it need to be on an object basis?

its the 2 checkboxes in your gi settings - nice and quick!
Do a test in a custom scene of the wrapper. You might be able to use an override mtl which has something with 0% opacity in the GI and refraction slots, or that might slow it down. Test the wrapper and ior of 1 too, I don't have personal experience with those.

You should have a scratch test scene for this anyway, it will be worth the time.

[trick]

Started to use this (http://www.splinedynamics.com/q-proxies/) Some months ago and helps quite a bit with masterplans. Particularly the workflow is helping a lot.

So might be worth a look!