Irradiance issues

[lisux]

Hi all.

Im' trying to learn GI in Houdini, my first attemp is to get irradiance effects.

I began with the GI irradiance video tutorial for H6.

I use the tutorial scene with the VEX GI shader, set the Irradiance to Full Irradiance.

Ok i've tested with different samples values and i get worse results than prman 11, but it needs more testing. My doubts began with the irradiance caching method used by H7. If i check Irradiance Caching in the Specific tab of a Mantra ROP, the cache is done in RAM?, because i don't specifying any cache file.This cache is like an .icf prman cache file? so it gets irradiance plus ambient occlusion? For the irradiance effect the render computes the shaders or only a "model of the shader" like prman?

The default error parameter is the same like the attribute "irradiance" "maxerror" of prman?

When i try to save the irradiance cache to a file, put the filename and sets File Mode to Write Only, render again, but no file is created Am i making some mistakes in the setup?

How can i see a photon map? (is there any app like the pixar's ptviewer?)

What is a direct photon map?

And for the last, how can i set what lights must emit photons?

Sorry for the message extension and thanks for you answers.

[aracid]

hey lisux

to create ur GI map on ur HD, under ur GI Shop, theres a photon map tab, specify ur map there, and under ur irradiance caching, under ur mantra ROP.

then specify write to create and read to bla bla bla. im sure u know what i mean.

just checking now, it doesnt seem to write the file out if u dont specify it under ur SHOP.

For the irradiance effect the render computes the shaders or only a "model of the shader" like prman?

im not too sure what u mean by that

ill try answer more a bit later

aracid

[stu]

For the irradiance effect the render computes the shaders or only a "model of the shader" like prman?

I think I see what you're getting at. I would assume that mantra actually evaluates the shader and does not just use an approximation of the diffuse colour for the irradiance calculations. I remember back in the BMRT days that when using a texture map you'd have to pass the irradiance solution an "average colour" to represent the texture - it wouldn't actually evaluate the surface shader to find out what colour the surface was actually going to be before bouncing light.

stu

[lisux]

hey lisux

to create ur GI map on ur HD, under ur GI Shop, theres a photon map tab, specify ur map there, and under ur irradiance caching, under ur mantra ROP.

then specify write to create and read to bla bla bla. im sure u know what i mean.

just checking now, it doesnt seem to write the file out if u dont specify it under ur SHOP.

I put the photon map name in the Specific tab and mantra ROP generates a photon map, then i put the name in the GI SHOP and the shader uses it.

Thats OK, but if i check Irradiance caching, put a file name in de Cache file, set Read/Write or Write only and render, no file is created .

So ican generate photon maps files but not irradiance cache files.

And in the GI SHOP you can see direct photon map, what is this?

[edward]

In you VEX Global Illumination SHOP, do you have it set to use Full Irradiance?

As for more photon map info, look under the Help Contents > Shaders > Vex > VEX Language Reference > Shading Contexts > Photon Shading Context.

[sidandmj]

Full irradiance must be used in order to write a cache for it.

check out my new rendering post, i have included a hip file that has a GI OTL embedded in it, maybe this will help . . .