Light map - what is this

[igsiv]

Hi,

I read about light map, and I don't understand - what is this?
Anybody, help me please !

1. How to build up trajectory for eye-ray?
2. How to calculate bounces for light map? Is this intersections of eye-rays with object's surfases? Or, what is the main algorim for determinating x, y, z - coordinates for bounces ?
3. How to calculate illuminations for bonces stored in light map? Is this direct illumination only ? Or indirect (diffuse) illumination too ? What does it mean "bounces in the path stores the illumination from the rest of the path " in more detail?

4. what is the main idea of the light map ?

Thanks in advance

[vlado]

Explaining all the things behind the algorithm will make a rather long post; if you are familiar with photon mapping, then the concept is extremely similar.

Best regards,
Vlado

[igsiv]

Vlado, thanks for the answer!
I secretly hoped to hear namely your answer. Long posts do not frighten me . I ask about light map here only because I can not find the answer somewhere else. This forum - my last hope (or I do not know where to search?). I know Photon mapping very well. It is possible, for this reason light map nonpluss me. Because photons are traced from a light source, and beams light map - from the camera.
BTW
The Most Important Question - how light map calculate illumination? Even very shortly?

[plastic_]

everything is explained here:

http://www.spot3d.com/vray/help/VRay...s_lightmap.htm

[igsiv]

2 plastic_
Thanks, I have already read it.

The light map is built by tracing many many eye paths from the camera. Each of the bounces in the path stores the illumination from the rest of the path into a 3d structure, very similar to the photon map. On the other hand, in a sense, it is the exact opposite of the photon map, which traces paths from the lights, and stores the accumulated energy from the beginning of the path into the photon map.

Is this the only available explanation of light map? It's not enough for me.