visibility of void / antimatter photon port surface in irradiance rendering

Hi Lars,

when you speak of irradiance rendering, do you mean running rzpict with -i option? In this case, surfaces get re-assigned a pure lambertian material with refl. coeff. of magnitude Pi (for primary ray hits), to automatically produce irradiance values on them.

All completely transparent stuff (glass etc) is of course excluded, but I remember that once there was an issue with Radiance classic, namely the problem that the antimatter material erroneously is not excluded from this material conversion process, and thus suddenly becomes visible. So this bug seems to have made it into Radzilla, too.

Well, this is one idea, without gurarantee that is really is the real problem. I Have to check it myself..

so long


----- original message --------

Subject: [Radzilla] visibility of void / antimatter photon port surface in irradiance rendering
Sent: Tue, 20 Jan 2009
From: Lars O. Grobe<[email protected]>

Hi Radzilla-users,

I made a strange observation that I want to share. Most probably it is
my fault, but it would be great if someone could shed some light (or
photons) onto this.

I define my photon port surfaces as such:

void antimatter photonPort
1 void

This should always be invisible. Right? At least I have no clue what
could be seen here...

I call rzpict with -apem on -apo photonPort and so on...

Now I have put a box of photonPort-faces (five faces - to the side and
to the top) around a sky-light. And - I can see this box as white in
front of my blueish glow sky on an irradiance rendering of the section
thru this system!

Well, I know that irradiance values can be wrong when calculated by
rtrace or rzpict with the photon map. Still, the visibility of a
non-defined surface makes me worried that something more fundamental may
be wrong here.

Any comments?

CU Lars.

I attach a VERY small rendering of the section of the skylight, which is
of such small file size that it should be acceptable. It still should
give a better idea of what I describe.

--- original message end ----