[Radiance-general] Lightpipes and rtcontrib

[Axel Jacobs]

Dear list,

I know this keeps coming up every now and then, but I just wanted to
check the latest state-of-the-art when it comes to simulating light
pipes. Here is what I gathered from various pieces of documentation,
posts, and the back of my head:

a) a forward raytracer such pmap seems to be the optimal solution, but
pmap has not been merged into Radiance Classic yet and only works with
Radiance 3.7

b) Radzilla, which also supported (some of the) pmap functionality
seems to be unmaintained.

c) the mirror material can only be used on planar objects, hence it's
no good inside a tube (inverted cylinder). How good would a metal tube
in combination with ridiculously high number of bounces be?

d) Guilio made some suggestions in this thread:
http://luminance.londonmet.ac.uk/radiance_mailinglists/general/2005-May/002708.html
about using some approximations in combination with a glow material

e) then there's the new rtcontrib program
(http://luminance.londonmet.ac.uk/radiance_mailinglists/general/2005-May/002710.html):
"Rtcontrib can also be used by the more adventurous among you to
compute input/output relations for devices such as light pipes and
shading systems, although I have yet to test such an approach,
myself." --Greg
There is a directory ray/src/rtcontutor, but the example explains
rtcontrib's use for daylight coefficients, not light pipes. I
personally can't quite work out how it would possibly replace a
forward raytracer, so has anybody been adventurous yet used it for
this?

f) How about gathering the external environment with a mkillum across
the pipe's entrance, then spreading the light in the interior using a
second mkillum at the pipe's exit?

Many thanks for sharing your thoughts

Axel