Mental Ray error message?

[colicoid]

I get this error from MR and then the render goes into an eternal loop it seems:

RCGI 0.4 warn 362004: no photons stored after emitting 10000 photons from light "spotLightShape5" (tag 546)

I removed all the spotlights from my scene and then it worked (rendering black). Any ideas on what is wrong here?

[McGergs]

you have caustics on but do not have any photonic materials in your scene.

[colicoid]

Actually, caustics are switched off.
After some extensive surfing on the net and hours of tinkering I found a solution.

It seems that some of my photons (at least 10k of them) do not hit any objects and simply continue in thin space for eternity. I managed to fix the problem by creating a polygon sphere and make it large enough to surround my whole scene. That way, stray photons eventually hit the sphere and are hence "collected". By disabling primary visibility on the shape node, the sphere does not appear in the final render.

My scene is an exploding logo so in the beginning all the pieces are there, close to the lights. My batch render stopped after 51 frames because the pieces that make up the logo was now scattered enough to not recieve any photons.

Hope this saves some time for sombody else... :)

[mrcorvus]

I had the semae problem and I found this:

GI photon maps vs. caustic photon maps

Photons that are specularly reflected or refracted are stored in the caustic photon map; all other photons are stored in the global illumination map.

So the objects in the scene mus have some specular on their texture.

As the Shinyness parameter of the photon shader attached to an object increases, specular highlights become smaller and the likelihood of specular reflection increases. In this case, more photons migrate from the global illumination map into the caustic photon map, decreasing the density of the global illumination map. (Similar considerations apply to the Translucence parameter, but in the opposite direction: when Translucence is increased, photons migrate from the caustic photon map into the global illumination photon map.)