Very basic question:
When simulating uniform sky, I see that usually “source” geometry is used, with 180degree angle.
However, “source” also has a direction vector associated with it. Seeing as the sky is uniform, what’s the physical meaning of this directionality?
It’s so that Radiance ‘knows’ that the sky is up. Which isn’t as odd as it sounds, since a 180 source with a direction vector ‘0 0 -1’ is used to model the ‘glowing’ ground. See Section 2.3 here:
Daylight Experts Ltd.
Expert Witness | Simulation | Measurement | Conservation
Associate Editor Lighting Research & Technology