clipka <ano### [at] anonymousorg> 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

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