[Radiance-general] rtrace -i -I flags

[Bleicher, Thomas]

Jelle.
 
As Giullio has already explained
 
-i    will return the value for a 'light meter' at (x,y,z) pointing in
direction (dx,dy,dz)
      Only that one point will be calculated.
 
-I    will return the value for virtual light meter at (x,y,z) pointing
in direction (dx,dy,dz)
      but it will sample the whole hemisphere around the direction
vector.
      Basically rtrace introduces a virtual plane and turns the 'virtual
light meter' around
      to get the value of a point on this plane. You have to increase
-ab by 1 to get the
      same number of effective bounces as with '-i'.
 
Try a simple scene with both options and low -ab values (0,1,2).
 
If you print origin and direction of the rtrace ray as well you will see
that '-I' changes
them. Quite confusing if you're not prepared for it.
 
Thomas
 


________________________________

	From: radiance-general-bounces at radiance-online.org
[mailto:radiance-general-bounces at radiance-online.org] On Behalf Of Jelle
Feringa / EZCT Architecture & Design Research
	Sent: 02 March 2007 14:38
	To: radiance-general at radiance-online.org
	Subject: [Radiance-general] rtrace -i -I flags
	
	

	Hi,

	 

	I'm running a simulation with rtrace, where I've set -I to
compute irradiance rather than radiance values.

	Though reading the man pages, I do find the explanations of the
flags somewhat confusing:

	 

	-i 

	Boolean switch to compute irradiance rather than radiance
values. This only affects the final result, substituting a Lambertian
surface and multiplying the radiance by pi. Glass and other transparent
surfaces are ignored during this stage. Light sources still appear with
their original radiance values, though the -dv option (below) may be
used to override this. This option is especially useful in conjunction
with ximage (1) for computing illuminance at scene points. 

	 

	-I 

	Boolean switch to compute irradiance rather than radiance, with
the input origin and direction interpreted instead as measurement point
and orientation.

	 

	In what cases should one use the -i flag and in which cases is
-I the preferred option?

	I find it hard to make the distinction from the docs.

	 

	Thanks,

	 

	-jelle 

	 


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