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# How to create an 10.000 lux overcast grey sky?

Hello Again, everything works fine so far, but as I now want to get the illuminance in a room I followed the radiance_tutorial and end up in the following problem: When I use the provded sky.rad and create the sky.mat using gensky as described in the tutorial, I result in the following:

$echo 0 0 0 0 0 1 | rtrace -I -ab 1 octrees\sky.oct #?RADIANCE oconv skies\sky_10klx.mat skies\sky.rad rtrace -I -ab 1 SOFTWARE= RADIANCE 4.2a lastmod by on w015t-001 CAPDATE= 2015:09:15 11:56:42 GMT= 2015:09:15 09:56:42 FORMAT=ascii 4.751300e+001 5.813355e+001 6.707717e+001  and echo 0 0 0 0 0 1 | rtrace -I -h -ab 1 octrees\sky.oct | rcalc -e "$1=179(.265$1+.670$2+.065$3)" 10025.4983  This is as near as I can get, but the sky is not grey. Can anyone provide me with an answer? Thanks, Fabian edit retag close merge delete ## Comments what do you mean the sky is not grey? Can you show the contents of your sky_10klux.mat and sky.rad files? ( 2015-10-07 09:57:47 -0500 )edit ## 1 Answer Sort by ยป oldest newest most voted Radiance is a monte carlo simulation, so you're not likely to get exactly 10,000 lux but you can get closer by increasing the number of samples. To do that set -ad to something high like 50,000 and set -lw to 1/ad (2e-5) and you should get closer to 10,000 lux. The command looks like this: echo 0 0 0 0 0 1 | rtrace -I -h -ab 1 -ad 50000 -lw 2e-5 octrees\sky.oct | rcalc -e "$1=179(.265$1+.670$2+.065\$3)"


The more samples you send the more you'll converge to the correct result.

As for your sky not being grey, that is likely due to the parameters you're using for your sky glow material. Is this what your sky material looks like (from scene 0 tutorial)?

skyfunc glow sky_glow
0
0
4 0.9 0.9 1.15 0


The "0.9 0.9 1.15" is the RGB color assigned to the sky. To make the sky grey change them two be one:

skyfunc glow sky_glow
0
0
4 1 1 1 0

more

@Andyrew: Thanks for your help. Having the sky_glow values set to one resolves in an 10000.77 lux grey sky. Fabian

( 2015-10-09 04:36:51 -0500 )edit