[Radiance-general] Rendering large space with small detail (small picture now attached!)

[Lars O. Grobe]

> I want to be able to test the daylight and sun penetration in the mall 
> space during different sky conditions eg 9am 12pm 3pm sunny sky and 
> also an overcast sky. So in hindsight I should've used the CIE 
> overcast. However, when I simulate with sunny sky conditions I get the 
> same resolution and rendering problems.
>
> Any more thoughts?
>
> Paul.
Hi Paul,

using not the uniform sky does not solve the problem, I guess that John 
asked because the uniform sky is not really a model of what you could 
observe in nature, so few people use it for anything but testing.

To solve your problem, several comments and hints have been given, and I 
would suggest that you try these. As a note, the mkillum tool is 
actually a way to get useable results without setting ambient parameters 
too high, a performance boost so to say, In your case, you would have to 
expect really high rendering times without such techniques.

If you wonder why you see the splotchy shades, look into how Radiance is 
rendering the ambient. The problem is the limited number of sample rays 
sent out for each bounce, to random directions. So for one point, most 
rays may hit the shade, while for a point just a cm aside, which should 
receive more or less the same irradiation, you may be lucky enough to 
hit the sky with all sampled rays. And than, this calculation is not 
done for each point in space, but only if the variation exceeds limits, 
the ambient resolution enforces it, .... and so on. So you COULD set ar, 
as very high, increase the ar setting, set a low aa, and wait.

The mkillum tool will optimize the calculation a lot, as it replaces the 
complex geometry outside the scene by a light source, so that is why I 
recommended it. It is always useful in cases of so-called complex 
fenestration, and your sun-shades are. If you think very creative, you 
could even consider the layer of internal sunshades as 'complex 
fenestration' (ok, no glass, but similar problems here), so I added the 
idea to have a mkillum surface here, too. But I guess that mkillum for 
the vertical clerestory windows, skyfunc for the horizontal skylight, 
and moderate ambient settings for the scene than should give acceptable 
results.

Do you have the book "Rendering with Radiance", as well as Axel Jacobs 
tutorials? These should give you an idea why you experience problems 
with you scene, as well as strategies how to solve these. And you should 
find examples on how to use mkillum, too.

CU Lars.