solarbr

Dear all,

if I read gensky.c (line 267) correctly, then the solar brightness is
constant for sin(sun altitude) below 0.16 which is an altitude of about
9.2deg.
Does that mean to say that RADIANCE skies can't be trusted for (very) low
angle sun?
Is there a scientific, computational, or philosophical reason behind this?

Cheers

Axel

Hi Axel,

It's probably fair to say that gensky can't be trusted to produce accurate absolute luminances for the sun OR the sky at ANY altitude. Skylight is simply too variable to be pinned down, even on average, without considering the local climate. In the case of low altitude sunlight in particular, there are a lot of highly variable atmospheric effects at play, which is why we don't see many reruns of the same sunset. In the code for gensky, I was going by some general ballpark values taken from Wyszecki and Stiles (Color Science), and it's a really crude estimate.

For accurate values, you'll have to come up with your own "sources" and set the -B and -R options accordingly.

-Greg

ยทยทยท

From: "Axel Jacobs" <[email protected]>
Date: March 29, 2004 6:56:19 AM PST

Dear all,

if I read gensky.c (line 267) correctly, then the solar brightness is
constant for sin(sun altitude) below 0.16 which is an altitude of about
9.2deg.
Does that mean to say that RADIANCE skies can't be trusted for (very) low
angle sun?
Is there a scientific, computational, or philosophical reason behind this?

Cheers

Axel