Hi Jia,
It seems that you posted this question twice to the mailing list.
The main effect of a "parallel" source is that its intensity does not diminish with distance. The closest you can come to a parallel local light source in Radiance is to use the "spotlight" material with a very long direction vector, indicating that the virtual source is far behind the emitting area.
Spotlight
Spotlight is used for self-luminous surfaces having directed output. As well as radiance, the full cone angle (in degrees) and orientation (output direction) vector are given. The length of the orientation vector is the distance of the effective focus behind the source center (i.e., the focal length).
mod spotlight id
0
0
7 red green blue angle xdir ydir zdir
Something like:
void spotlight long_throw
0
0
7 1e5 1e5 1e5 1.0 0 0 -1000
long_throw ring spot
0
0
9
0 0 3
0 0 -1
0 .1
The above will create a 1-degree spread spotlight with a 1000-meter focal length, meaning that the effective emitting position is 1000 meters behind the emitting surface (a 10cm disk in the ceiling in this case). This should give you the effect you want, even if the sample rays to the source are not always parallel.
If your actual purpose instead is to generate perfectly sharp shadows, you can do this by shrinking the size of the emitting area (and increasing the RGB arguments of spotlight to compensate).
-Greg
ยทยทยท
From: Jia Hu <[email protected]>
Date: February 20, 2014 5:13:57 AM GMT+01:00Hello,
how could I generate some parallel light like sunlight? Should I use "source" identifier? The parallel light source is located in a room.
What if I want to generate a parallel light beam (emitting from a tube)? I am currently using a tube and place a spheric shape light in that tube, but it may not be parallel emitting from the tube..
Thanks,
Jia