[Radiance-general] Lightpipes and rtcontrib

[Greg Ward]

Hi Axel,

Responses inline...

> 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?

Would work for the sky, but not the sun.

> 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?

I gave it a go for illustration purposes at the 2006 Radiance  
workshop.  You can download a QuickTime movie of the presentation from:

	http://www.radiance-online.org/radiance- 
workshop5/2006_Radiance_Workshop/

It's the talk entitled, "Applying the Radiance rtcontrib program,"  
but heed the warning and download the QT movie rather than hitting  
the link on your browser, because most browsers (including Safari)  
barf on it.  The key part you want to check out is "Step 2" in the  
mirrored light pipe example.  I'm using flat surfaces, but only for  
comparison purposes.  The rtcontrib approach should work for any  
geometry.

> 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?

Again, this wouldn't work for the solar component.

-Greg