SV: Re: [Radiance-general] Lux-values for points in a plane

[Per Haugaard]

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 Thank you very much for your reply: I really appreciate your help. But it still troubles me why I cannot get the correct ratio between the output and the entered LT-value for the window. Please refer to the below.
   
  > 6.216 0.00 1.8 0 -1 0 (window)
  > 6.216 0.05 1.8 0 -1 0 (black wall located 0.05 m behind the window  
  > - in fact all walls are black)
  > 
  > The Window (LT=0.72):
  > void glass window_glass
  > 0
  > 0
  > 3 .78 .78 .78
  > 
  > cat IllumKoordinater.pts | rtrace -I -ab 4 -h -w -oov kontor.oct |  
  > rcalc -e '$1=$2;$2=179*(.265*$4+.670*$5+.065*$6)' > lux.dat
  > 
  > Output
  > -1       4883.69
  > -0.95  3049.70
   
  > If I understand the above correctly you are calculating two points:
 > one in front of the window, one behind it. The black walls are used
 > to swallow all light reflections on the inside so you will only have the
 > transmitted light left.
 
 
  Yes I only want to evaluate on the transmitted light through the window. I am interested in, later on, to calculate the transmitted light through the window with external shading based on a CIE-standard overcast sky.
  
 > Two improvements:
 
 > 1) Move the wall further back or place your second point at ie. 0.04. If
 > the calculation point coincides with the wall everything is possible.
 
 
  When I calculate the transmitted light at any other point in the room e.g. 0.04 (away from the black wall) the calculation coincides with the window (LT=1). 
  
 > 2) Don't use a box at all. At the perimeter there is a dark horizon 
 > (black walls) which is taken in into the calculation. You could 
 > create a sphere of the material around your calculation point instead.
 
 I’m not sure what you mean here.
 
 
  > Two things worth noticing here. The output coordinates are not  
  > listed correctly which gives me the suspicion that lux-values are  
  > is not calculated for the correct coordinates. Furthermore the  
  > ratio between the output are not according to the entered LT-value  
  > for the window (0,62 vs. 0,72)
  
 > The first is the result of rtrace's interpretation of the '-I' switch 
 > (uppercase 'I'!) rtrace creates a 'virtual surface' at the calculation 
  > point and starts the calculation from the point of the view vector. 
  > In your case these are (6.216+0, 0+-1, 1.8+0) and 
  > (6.216+0, 0.05+-1, 1.8+0). Your rcalc command prints only the y- 
 > coordinate.
   
  Okay, so the calculation is carried out for the correct input coordinates.
   
  > The second problem I can't explane but depending on the size of your
  > box the 'dark horizon' might have some influence here.
   
  My reference point in the room should coincide with the center of the window. I appreciate any help on solving why the ratio between the output and the entered LT-value for the window (0,62 vs. 0,72) differ.




Best regards


Per Haugaard





  

______________________

Per Haugaard,
Griffenfeldsgade 33, 2.tv
2200 København N
Denmark

mobil:  +45 26 39 06 40
E-mail: perhaugaard at yahoo.dk
       
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