glow&spotlight material

Hi, This is woogie.

I am trying to study material characteristic in Radiance by using Desktop
Radiance in the DOS mode.

I have some problems with glow and spotlight material.

I made a simple scene with only two surfaces facing each other.
One of surfaces is light source and the other is plastic.
the plastic surface (1x1m) is 5m apart from the light source material(1x1m)

And I plugged in different light source material to see if there is differernt.

Light and illum material result in the same illuminance value as that by hand
calcuation.

When it comes to glow material, it seems to me odd.
The first, It is said that the fourth argument, maxrad in the glow material can
be negative, zero, and positive.

When the fourth argument is zero, illuminance value on the floor(1x1m) which is
5m apart from the glow material(1x1) is not uniform.

Light amd illum material result in the uniform illuminance value on the floor
with the same geometry material setting.

It seems to me that rendering parameter might not correct because the center of
the floor is darker than the edge of the floor or it comes from Desktop
Radiance or it is because I did not understand the fourth argument in the glow
material.

If anyone knows of my problem, please let me know.
I am linking a file below

http://www.personal.psu.edu/users/w/x/wxo110/radiance.htm

I appreciate any comment about it.
Thanks!

···

From woogie.

The fourth argument can be set to 0. It is important to crank up the rpict ambient calulcation or you will miss the glow source, because it can only be caught by -ad and -as rays

rpict -ab 1 -ad 8000 ...

Dr. Moeck

···

-----Original Message-----
  From: WOOK JEA OH [mailto:[email protected]]
  Sent: Sun 4/25/2004 4:17 PM
  To: [email protected]
  Cc:
  Subject: [Radiance-general] glow&spotlight material
  
  Hi, This is woogie.
  
  I am trying to study material characteristic in Radiance by using Desktop
  Radiance in the DOS mode.
  
  I have some problems with glow and spotlight material.
  
  I made a simple scene with only two surfaces facing each other.
  One of surfaces is light source and the other is plastic.
  the plastic surface (1x1m) is 5m apart from the light source material(1x1m)
  
  And I plugged in different light source material to see if there is differernt.
  
  Light and illum material result in the same illuminance value as that by hand
  calcuation.
  
  When it comes to glow material, it seems to me odd.
  The first, It is said that the fourth argument, maxrad in the glow material can
  be negative, zero, and positive.
  
  When the fourth argument is zero, illuminance value on the floor(1x1m) which is
  5m apart from the glow material(1x1) is not uniform.
  
  Light amd illum material result in the uniform illuminance value on the floor
  with the same geometry material setting.
  
  It seems to me that rendering parameter might not correct because the center of
  the floor is darker than the edge of the floor or it comes from Desktop
  Radiance or it is because I did not understand the fourth argument in the glow
  material.
  
  If anyone knows of my problem, please let me know.
  I am linking a file below
  
  http://www.personal.psu.edu/users/w/x/wxo110/radiance.htm
  
  I appreciate any comment about it.
  Thanks!
  
  >From woogie.
  
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  Radiance-general mailing list
  [email protected]
  http://www.radiance-online.org/mailman/listinfo/radiance-general

Hi Woogie,

What you are seeing is likely the result of a known anomaly in the hemispherical sampling pattern used by the indirect calculation in Radiance. I think Charles Ehrlich was the first to point this out to me -- the polar sampling I use on the hemisphere means that the exact pole is never sampled, and there is a slight dip in the response to indirect surfaces directly overhead as a result. Since this is how you arranged your scene, it is likely that this is the source of the odd dip in value towards the center of the surface illuminated by the glow source, as the glow only contributes to the indirect portion of illuminance.

To fix this problem would complicate the code and only reduce errors in some very odd circumstances. There are many other circumstances that cause similar biases, so I never thought it worthwhile to change it.

-Greg