[Radiance-general] Radiosity method implementation on Radiance

[Greg Ward]

As I've noted when asked this question in the past, radiosity is faster for simple spaces with many interior reflections.  Complex spaces quickly become expensive to compute, and the meshing of them can be a nightmare.

If you need to compute the illumination of an empty box, then anything is going to be fast.  If it's really, really important for you to compute empty boxes in a second or two, then radiosity is the way to go.  If you can wait 30 seconds, Radiance works, too.

If you have a complex building to render with trees and sky, have fun doing it with radiosity!

Cheers,
-Greg

> From: Germán Molina Larrain <gmolina1 at uc.cl>
> Date: June 21, 2013 8:42:14 AM PDT
> 
> Thanks for the answers Lars!
> 
> I am thinking on "one-zone" simple scenes, without furniture. I was checking out Lightsolve algorithms, and for them, this approach seem to be working well. I am thinking on something similar, but not the same.
> 
> Also, a friend of mine did some work on lighting simulations, and claimed that Radiosity was actually much faster than Radiance for those calculations.
> 
> Anyway, lets see what others can say about this... I was aware of the hybrid-stochastic-deterministic capabilities of Radiance, but I am not sure what that exactly means, so I cannot say if this would be faster or not.
> 
> THANKS!
> 
> German
> 
> 
> 2013/6/21 Lars O. Grobe <grobe at gmx.net>
> 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.
> 
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