Light Cache questions

[mattsmith]

Hi guys, it's been a very long time since I've spent any time with Vray, so I'm trying to get my head around some of the new settings.

From what I've read the Light Cache isn't adaptive, but in the rollout there's an adaptive sampling option...what's up with that? Turning it on seems to make the LC generate super slow...are there any advantages to using it?

Also I've read that using World Scale isn't great for big outdoor scenes with lots of details (makes sense) but then I've also read that for fly-through mode it's better to use world scale...why is that? Which should I use for say a super-heavy forest with lots and lots of geometric detail?

finally, the Retrace threshold defaults to 1.0, I'm assuming this determines at what point Vray decides to do some extra path tracing, but what is that 1.0 relative to? When should I adjust this value? Been searching the docs and forums but I can't find anything on these >_<

thanks for any help!

matt

[Zdravko]

there's an adaptive sampling option...what's up with that?

The Adaptive sampling option is usually used when rendering caustics. It helps to reduce the noise in the LC by forcing V-Ray to store additional information for each light cache sample.

I've also read that for fly-through mode it's better to use world scale...why is that?

Also Screen space is best used for stills or animations where the LC is calculated for each frame separately, because it doesn't amass light information. The Fly-through mode on another hand sets all the samples in one map, therefore World space assures that the samples are uniformly spread along the whole animation path.

what is that 1.0 relative to?

Furthermore about the Retrace threshold, when this option is on V-Ray will use brute force sampling in the places where LC sampling produce artifacts. The default value of 1 is equal to one LC sample in a particular point. The best way is to run some test with different values in order to determine the right one for the case.

More information can be found here: http://www.spot3d.com/vray/help/maya...lightcache.htm

[bigbossfr]

Hi,
Another question : if i want to use "Use light cache for glossy rays", if :
- i have static objects : i have to render 1 time the LC
- i have moving objects : i have to render LC for each frames
- i have static object but moving lights : i have to render LC for each frames

Good ?

[Zdravko]

There is no difference whether you enable "Use light cache for glossy rays" option or not. Always use the LC the way you mentioned.

[bigbossfr]

There is no difference whether you enable "Use light cache for glossy rays" option or not. Always use the LC the way you mentioned.

So, for moving objects, i have to render LC for each frame.
There is no "animation mode" for the LC, so i have to use preRender mel script to set the LC for each frame.
I did this, it works, but and "animation mode" will be better because i have to render 1 batch by frame (1-1,2-2,3-3,4-4...).

[Zdravko]

By setting the LC in Single frame mode it will automatically calculate LC map for every frame, when you have animation.
Also what do you mean by

have to render 1 batch by frame (1-1,2-2,3-3,4-4...)