[Radiance-general] Images too bright with gendaylit

[Jan Wienold]

Hi Joe,

why do you think it is too bright? Is the luminance to high? I guess you 
just have to adapt your exposure setting for the image.

The physics for gendaylit and your parameters is correct:

1. test of luminance of the sun (ray in sun direction):

gendaylit -ang 90 0 -W 900 200 >sky.rad
oconv -f sky.rad >sky.oct

echo  0 0 0 -0.000000 -0.052336 0.998630 |rtrace -h sky.oct | rcalc -e 
'$1=47.4*$1+120*$2+11.6*$3'
result: 1.356104e+09 cd/m2

This value looks reasonable - the max is about 1.6 e9 cd/m2

2. test of irradiance (sensor also looks towards sun):

gendaylit -ang 90 0 -O 1  -W 900 200 >sky_irr.rad
oconv -f sky_irr.rad >sky_irr.oct
echo  0 0 0 -0.000000 -0.052336 0.998630 |rtrace -h -I+ sky_irr.oct
result : 8.998834e+02   W/m2

Equals the direct irradiance which was "put" into the model (the sky is 
ignored, as in your example).

cheers

Jan


On 08.08.17 09:17, Joe wrote:
> Hello,
>
> when I use gendaylit to create a sun my images are too bright.
>
> The command used is
>
> gendaylit -ang 90 0 -W 900 200
>
>
> void light solar
> 0
> 0
> 3 7.576e+006 7.576e+006 7.576e+006
>
> solar source sun
> 0
> 0
> 4 -0.000000 -0.052336 0.998630 0.533000
>
> This will put the sun to the zenith with reasonable values
> for direct normal and diffuse irradiance in W/m^2.
>
> Correct so far?
>
> I removed the skyfunc, just the sun source is active.
>
> I put together a simple scene:
> - plastic cylinders as coordinate origin,
> - large brown ground plate
> - dielectric spheres (I just love those :)
>
> Here is an image with renderings of different sun settings:
>
> http://imgur.com/hOqCpmY
>
> When I use the sun as stated above the image on the right
> side is rendered. Much too bright.
>
> Reducing the parameters of void light solar:
>
> middle image (7.576e+005 7.576e+005 7.576e+005 )
> left image (7.576e+004 7.576e+004 7.576e+004)
>
> Viewed with default parameters of rvu.
>
> Do you have an idea what I am doing wrong
> or might have missed?
>
> Kind regards,
> Joe
>
>
>
>
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-- 
Dr.-Ing.  Jan Wienold
Ecole Polytechnique Fédérale de Lausanne (EPFL)
EPFL ENAC IA LIPID

http://people.epfl.ch/jan.wienold
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Phone    +41 21 69 30849