[Radiance-general] Radiosity method implementation on Radiance

[Lars O. Grobe]

Hi German!

> I am thinking on implementing a hybrid methodology between Radiosity
> method and Ray-tracing, for accelerating some calculations (by giving up
> accuracy, maybe)

Did you think about in what use cases radiosity may be faster, and in
which it wouldn't? And are you aware of the "hybrid" rendering approach
used by Radiance? Especially the way that the ambient cache is working
as a means to accelerate the stochastic diffuse-indirect calculation
that a radiosity renderer aims at?

> I think I can make algorythms to subdivide polygons into meshes,
> however, what I do not know how to do is:

I think most of this is already happening when you are using the ambient
cache.

> *1.- Calculation of View (Form) Factors:* I guess a straitforward way is
> to calculate them by randomly sending rays from one surface to the rest
> of them, but I do not know how to do that (or use octrees). (k/N would
> be the view factor Fij... where k is the number of rays that falled into
> j from i, and N the total number of rays sent)

If you want to do this using scripts and the available tools, you could
step through all surfaces in a scene file. There are tools to do the
sampling available.

> *2.- Render:* After I have the Radiosities of every polygon. How can I
> make a render? I guess I can use *vwrays *somehow, but I am not sure how
> to check which polygon am I "seeing", in order to use the calculated values.

You can tell rtrace to output object names instead of radiance or
irradiance values. You can also get both the name of the object and its
radiance. This would even allow to add the radiance value of a scene
with -ab 0 and the precalculated "radiosity" value. Somehow what most
radiosity renderers do to achieve sharp shadows (they add a
raytracing-step for direct calculation).

Still I have doubts that this can be faster than the current
implementation.... :)

Cheers, Lars.