[Radiance-general] Rendering large space with small detail (small picture now attached!)

[Rob Guglielmetti]

On May 19, 2009, at 8:09 PM, Paul Chilton wrote:
> In the .rif file, I'm creating the mkillum function which I've used  
> the tutorial example is; mkillum= -av 18 18 18 -ab 0 . I then go  
> into the .rad file to find the properties and geometry of the  
> skylight and then copy and paste those values and descriptions  
> separately into a new .rad file and save it as window.rad. In  
> the .rif file I then refer to this window.rad file by specifying  
> illum= window.rad. My interpretation of this procedure is that  
> rather than the ambient being the generator of light into the space  
> it is now the window itself which is the light source.

Hi Paul,

So you're on your way. Lars has explained that mkillum will do the  
"bringing of the direct component closer to your scene" as I  
suggested. A couple of other pointers:

You want to create impostor geometry or define your skylight apertures  
as illum sources. You do this by adding "illum=" lines to the .rif  
file. Let's say you have a skylight defined by a skylight.rad file,  
that describes the polygons that make up the skylight opening; you  
would remove that reference from the "scene=" line(s) and add an  
"illum=" line. You are telling rad to take any polygons defined in the  
illum= files and do a backwards raytrace from those polygons and out  
into the scene beyond. Generally this is the exterior environment, and  
as such the rays traced stand a much better chance of hitting the sun.  
The results of this raytrace operation are saved and applied as a data  
file to the polygons defining the skylight or aperture and that  
aperture becomes a light source. I would not worry about an -av value  
for your mkillum= line, but I would definitely increase the -ab value  
to 2 or 3, and -ad 512.

You should not do anything to the .rad files from there. rad is great;  
if you tell rad (via the illum= line(s)) which surfaces should be  
precalculated as light sources, rad will manage the creation of these  
secondary light sources as they are called and create its own separate  
rad files that substitute the precalculated illums for the  
calculations and/or renderings. Definitely look at the rad manual page  
for more info on this...

- Rob Guglielmetti