Global Irradiance how to do and what can it do

[tom schuelke]

hi Guys

I´ve been using Vray now for a while and i am impressed by the speed and ease of use. But still feel that there is much to learn.

What i absoluteley didnt use yet and dont know what it does, is the "Global Irradiance map" with "Photon mapping". so what is the concept behind this, how does it work and what can i do with it that i cant do with "irradiance computing" (maybe fast animation wihout flickering and also animated lights and objects ? )

mayby there´s a tutorial somewhere that could better explain it ?

thanks.

[natty]

I think when you use both solutions together you will get a better depth of solution and the photon map seem's to pick up more detail.......
try photon map on it's own .......very fast ........you will have to use vray materials to get photon maps to work.


Natty

[PATER]

I had to answer on this one...

Hey Tom

As far as i understood, photon mapping helps raytracers when shooting their rays. Normally, the renderer takes a point and shoots random rays in the scene to collect the diffuse light information at that point. Although this is the real world approach, (in reality the number of rays is of course infinite and the way of light is actually the other way around) it's not that intelligent cause most of the light comes from a certain lightsource and/or angle. Photon maps provide the Renderer with the information of the direction the most light is coming from. There are 5 photons @ a certain point? So the Renderer shoots it's rays primarly in these 5 directions and can be sure that it'll hit a source of direct or indirect light. Because emitting photons from a lightsource and bouncing them around in the scene is much faster than tracing all the needed rays from the camera, photon mapping can bring you much more lightbounces in less rendertime.

Well... the Chaos-Guys say in their photon map tutorial: "A third advantage of photon maps (although not currently used in VRay) is to guide the raytracer to the more important parts of the scene." and i'm actually a little confused by this statement.
The way i described it actually helps the Raytracer shoot it's rays... or is it just the QMC-Engine? If it's not how i described it, why is the rendering with global photon maps so much faster in Vray?
hm...

Well you can check out a few links in the meantime Tom:

A Basic Guide to Photon Maps in VRay
Goncalos photon-version of flipsides interior scene

It's not that easy to get good infos about photon maps in vray and i'm still not really into it yet. This is all i can post right now... hope that helps... (try vray.info too)

PATER

[tom schuelke]

Hallo Pater

Thank you for your answer. Yesterday i allreadey found the tutorial from Vlado, you´ve been talking about. It was very impressive to see those cornel box beeing computed about two to three times faster than it was with irradiance map only. Now i´ve been testing a little flighthrough. i am not shure. but i think there was much less flickering in the scene. so i am asking my selve, if the photonmap i reused for the animation is view independent.

I think so. so the next test will be how it does reakt with animated objekts and lights. (worst case scenario)

I had the impression, that the GI multiplyer in the Objekt settings reakts much stronger to changes than it does in irradiance renderings.

And i am asking my selve also, in which situations photonmapping is not better than combined photonmapping with irradiance in the first diffuse pass?

wellll i ve received your E´mail in my company and have wrote back to you.

by the way greetings from Hamburg, to Hamburg.

Tom