Reusing Light Cache?

[thomthom]

How does it work? Can I calculate Light Cache and Irradiance map for one scene, save it and use it for other scenes? Or will it only work for the same scene?

When will I have to create new maps? On light changes? Material changes?

[dalomar_cg]

Re: Reusing Light Cache?

I'll talk about them in general then go into the specifics of each one. You can save certain light solutions in Vray (in fact every one but DMC bc that works directly on the image), however there are a few things that you should know about saving solutions in order to make them work for you. First off, all of the solutions are based on the geometry/materials/lighting of your scene. In order for the lighting solutions to be valid, those three components must be intact (materials is the only on where there's some wiggle room, but not much). Therefore you can't move solutions around from one scene to another, and even within the same scene it takes care to make sure that a saved solution is still valid.

Secondly, in the case of IR and LC, the solutions are view specific. This means that those solutions are only valid for the view in which they were rendered. This is a way that v-ray uses to speed up the render process by trying to calculate only what is needed for what you see.

On to IR specific things...IR is the most flexible when it comes to reusing them. The structure of IR is essentially a bunch of 3d points that have illumination data assigned to them (determined during the render process). Because of the nature of how this data is structured, it allows it to be worked with in a much easier way. First off, you can merge two solutions together with the IRMap viewer. So this means that rather than having two separate maps for two cameras in a scene, you could merge them into one and not have to reload them from camera to camera.

The second thing is that you can do IR calculations that work from previously computed IR maps. Basically, if I had an IRmap that I saved from a given camera, and I had to move that camera over 5ft for a better view, I could use the IR map that I already had to help out with the calculations for the parts of the scene that are in both shots. And you can use this for all of the cameras within your scene, so by rendering out one IR map and adding to that map from camera to camera, you can have one IR map for all of the different views in your scene (this is very powerful). This is basically the concept that is used for rendering out IR maps for animations.

On to LC...Light Cache is much different than IR...To start, the data itself is not the little 3d points, but rather the whole raytracing structure that was used to calculate the solution (not 100% on this, so don't quote me on it). This means that it is much harder to bounce back and forth with LC maps...in fact, you can't at all. Basically, you can save/reuse a LC map for one view and one view only. There's no way to add to them, and once something changes then you will need to start over from scratch. The only exception to this (and its really not even an exception bc its not supported in SU) is LC for animations. For animations LC will sample along the whole path for the whole animation, and keep the raytracing structure as one. You can only use this for animations, not multiple cameras, bc Vray needs to know all of the places to look at the scene from and then interpolates between those places.

The last one I'll talk about (even though you didn't ask) is Photon/Caustic Mapping. This is a similar structure to IR maps, so we're talking about points in space with light data attached. The main difference between this method and the other two is that it is NOT view specific. Which means that once a solution is calculated, it is valid for the WHOLE scene, no matter what view you calculated if from or the view your rendering with. This has its advantages and disadvantages, but because the solution is valid for the whole scene, theres no way/need to add to it like IR calculations. Photon mapping is older, antiquated technology though, so its not very efficient for general lighting, and is mostly only used for caustic calculations.

The following link would be good to look at, as it talks about a bunch of the IRmap stuff I talked about
http://www.spot3d.com/vray/help/150R...ials_imap1.htm

[thomthom]

Re: Reusing Light Cache?

That's great information! Thanks!

I searched for the IR viewer, but I couldn't find any place to download it. Is it bundled with Max?

[dalomar_cg]

Re: Reusing Light Cache?

We don't have it here...we used to though...don't know what happened too it

[juan.carlos.rioja]

Re: Reusing Light Cache?

a question... is this process of saving the IR and using it just by setting the "from file" option as I read in the manual can be used in animations. I'm trying to improve the time I spend to make a video. Are there any options???

[dalomar_cg]

Re: Reusing Light Cache?

Thats pretty much required. For animations, you'll run the prepass to get a saved Irradiance map, then load that up via "From File" and render out the final images.