[Radiance-general] Re: implementing Radiance reflection model

[Greg Ward]

Hi Tarik,

The formula for K should be:

			             exp(-tan^2(delta)/alpha^2)
			  K =     -----------------------------------
			         cos(theta_i)*cos(theta_r) *4pi*alpha^2

How are you computing delta?  It is the angle between the half-vector 
and the normal.

Also, for large disk sources, the exact calculation for solid angle is:

	2pi*(1 - cos(theta_s/2))

Where theta_s is the subtended angle of the light source.  This is a 
insignificant correction to what you have for distant sources.

-Greg

> From: Tarik Rahman <tarik.rahman at ed.ac.uk>
> Date: January 11, 2005 7:05:40 AM PST
>
> Hi there
> I'm still trying to get the correct values for the Radiance reflection 
> model,
> they're close but not quite right. So for isotropic reflectance I get 
> K as below
>
>
> 			             [ exp(-tan^2(delta/alpha^2)]
> 			  K =     -----------------------------------
> 			         cos(theta_i)*cos(theta_r) *4pi*alpha^2
>
>
> and use the formula to get the returned colour as
> Li = Ii*projected_solid_angle(rho_diffuse/pi + rho_specular*K) where
>
> 				cos(theta_i)*PI*r^2
> projected_solid_angle =		-------------------								         
> dist_to_light^2
>
> and r is the radius of my spherical light source.
> when I do rview -vf view.vp -av .5 .5 .5 file.oct do I just add this 
> -av value
> for ambient light as below?
> Li = light.colour*projected_solid_angle*(rho_diffuse/pi 
> +rho_specular*K)
> + ambient;
>
> Thanks for any help
>
> Tarik
> --
> Tarik Rahman
> PhD student, Institue of Perception, Action and Behaviour
> School of Informatics
> University of Edinburgh