[Radiance-general] Radiance value of uniform sky

[Kam Shing Leung]

(The previous message doesn't seem to show up properly, and is therefore re-sent here without the attachment. Sorry for the duplication.)
   
  Dear all, 
   
  I am trying to obtain irradiance value on the surfaces of building blocks under daylight but encounter the following problems.  Could you shed some light on how they can be solved?
   
  1. Uneven distribution of the uniform sky 
   
  I produced a uniform sky using the –u option under the gensky function.  As measured from the fisheye view of the sky (both angular and hemispheric), however, the radiance of the sky slightly decreases towards the edge of the “circle”.  Is there a way to improve this situation?  Here are the parameters that I used for rendering the sky:
   
  > Rpict –vf view.vf –ab 0 –aa 0 –ar 128 –ad 4096 – as 1024 sky.oct
   
  2.  Different value obtain in each run
   
  I tried to render some building blocks (with homogeneous color and reflectance) and then obtain the irradiance of a point on the ground with rtrace.  Different values returns even if the inputs are identical.  The discrepancy can be as much as 4%.  Like the command line printed above, ambience parameters had been set at their maximum values.  Is there a way to obtain irradiance values with a smaller margin of error?
   
  Thank you very much for your help!
   
  Regards, 
  Kam

       
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