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Solar radiance in Hosek sky model

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I'm currently looking at the Hosek sky model and experimenting with the provided source code.

At the moment the results for arhosekskymodel_radiance() vs arhosekskymodel_solar_radiance() are confusing to me.

 

Using the spectral arhosekskymodel_radiance() and converting it to RGB gives me:

 

[attachment=31582:hosek_expected.jpg].

 

Notice that I manually added in a sun, but it only affects a very small area of the image.

 

Using arhosekskymodel_solar_radiance() and converting to RGB gives me:

 

[attachment=31583:hosek_actual.jpg]

 

In this case the sun is directly provided by the hosek model. The positions match but the color of the sky is completely different. I was expecting the exact same result, expect for the small area where the sun is visible. The bright point of the hosek sun is at the same position as my manually rendered solar disk, but I also get vastly different results for rays that don't directly hit the sun at all.

 

From looking at the interface I was expecting that I can call arhosekskymodel_solar_radiance() with the exact same parameters as arhosekskymodel_radiance() and it will just work. Is this assumption correct? Does anyone have experience with this model? I don't think it is a matter spectral to RGB conversion, as I use the spectral version of the hosek functions in both cases, so the conversion is identical. 

 

Could it be that arhosekskymodel_solar_radiance() should only be used when rendering the solar disk? But that would mean, that you can render an arbitrarily large sun that don't match the assumptions the hosek model makes.

 

EDIT:

After reading the comments in the code I'm now pretty sure that arhosekskymodel_solar_radiance() should only be used when rendering the solar disk!

Edited by B_old

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