[Radiance-general] different methods on irradiance calculation

[Greg Ward]

Hi Ali,

Multiprocessing is not supported under Windows using rtrace, unfortunately.

Mkillum is not advisable if you are just computing illuminance points.

Turning interpolation off with rtrace (-aa 0) is a reasonable thing to do for point calculations, especially if you have only a handful of values you are computing.  The payoff for the ambient cache is when you have many bounces and/or many calculation points.

Best,
-Greg

> From: Ali Fatoorechi <ali at surveymbs.com>
> Date: April 11, 2017 12:24:01 PM PDT
> 
> Hi Guys,
> 
> I am writing mainly to understand Radiance more on different methods on irradiance calculation on surface point while maintaining accuracy and speed.
> 
> - I can use rtrace with irradiance interpolation turned on and rely on high -ad( >1024) for direct light from sky.
> running Radiance on Windows, it didn't seem to do run it in multi processing(-n). I am not sure if this is supported on Windows?
> Also breaking the points in chunks and running separate rtrace processes didn't seem to speed it up much. 
> I don't go mad with -a numbers but the time tends to increase, sometimes up to an hour for a room on complex models. 
> 
> - I tried mkillum to increase the speed/accuracy but as the model is all triangles I get the "aiming failure" error messages,
>  and it was mentioned in another post that triangles are poor choice for light sources(due to the way Radiance samples
> direct lighting.) I guess mkillum may not be advised in this case? also the calc time increases linearly with with more illums in the model.
> 
> - rtrace with interpolation switched off, seems to be pretty quick. but as it is blind monte carlo there is a concern on accuracy on
> direct lighting I guess(unless using high -ad). I have seen the window glazing defined as glow in three phase method(and later to use genbsdf for T).
> I am not quite familiar but if glow material is part of the direct lighting, would this make it a better approach than pure MC?
> 
> thanks and apology for this long post,
> Ali
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