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# The global cubes algorithm by Immel et al: Is it a particularization of discrete ordinates?

## The global cubes algorithm by Immel et al: Is it a particularization of discrete ordinates?

(OP)
There are situations where the overlap of knowledge and research between radiative heat transfer and radiosity confuses me. While radiosity (a computer graphics technique) was developed using radiative heat transfer as its base ground (acknowledged fact by the early/pioneering radiosity researchers), however there are times where I don't understand if they forgot to cite some heat transfer papers, or if actually they are talking about a different thing.

One such example is non-diffuse reflection. For example, in "A Radiosity Method for Non-Diffuse Environments" by Immel, Cohen, Greenberg, they propose using "global cubes" which basically discretize directions for the solid angles of each cell in each cube. This really sounds to me like the discrete ordinates method, but however in their paper they don't cite Chandrasekhar nor mention discrete ordinates at all. Am I missing something, or maybe they developed their algorithm without knowing the existence of discrete ordinates?

What's more, you can read a further development of the "global cubes" algorithm, using spherical harmonics to avoid aliasing artifacts due to the discretization of directions, this time in the paper "A global illumination solution for general reflectance distributions" by Sillion, Arvo, Westin, Greenberg, and they don't mention the discrete ordinates method either.

Am I right in concluding that they are talking basically about ways of applying the discrete ordinates method, but that for some reason they didn't know of its existence? Or am I missing some detail which makes their approach totally different?

### RE: The global cubes algorithm by Immel et al: Is it a particularization of discrete ordinates?

I would start by contacting Prof. Donald P. Greenberg at Cornell University. No one besides the paper authors can help you discover what the authors were thinking.

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