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> clipka <ano### [at] anonymous org> wrote:
>> Am 03.04.2017 um 11:26 schrieb muyu:
>>
>>> 2) The calibration factor may be wrong. I simulated the reference panel and set
>>> the diffuse as 1.0. The value is the same over different viewing angles. But I
>>> found that when I increased the height of the light source, the value may change
>>> from 239 to 240 (why?). Then the reflectance in the scene is caculated by diving
>>> this calibration factor. Is this the right way?
>>
>> I'm not sure I really understand what you are doing there.
>
> I am simulating the canopy reflectance under different solar and camera
> configurations.
>
> The incident solar radiation is parallel but not always nadir. For instance, I
> set the light source (zenith anglen 20 degree)
> light_source{<0,36.397,100> color rgb<0,1,0> parallel}
>
> Then for a planar surface with optical properties `finish { diffuse 1 specular 0
> ambient 0 }`, I got reflectance 239 (or 240 when the light source is moved
> further away). This value was considered as the calibration factor (f) for
> reflectance 1.0.
>
> Then for given camera configuration, I render the image of the targetting canopy
> with the same light source. Then the encoded pixel value of the image was
> averaged (color) and divided by the calibration factor instead of 255 to get the
> canopy reflectance (Ref), i.e. Ref = color/f.
>
> Or it should be Ref = color/255 + (1 - f/255) ?
>
>
> Great thanks again.
>
> Shouyang
>
>
If your light is not dirrectly above but at an angle and pointing at a
given point, then, placing it higher have the effect of making it closer
to been sttaight up.
When mooving the light up, be sure that you also move it laterally in a
proportional maner. One way would be to place it along a given axis at
the desired distance, then use a rotate statement to actually place it
at the desired location.
Use :
light_source{-1000*z rgb 1 rotate <75,0,0>}
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