[Radiance-general] trying to implement isotropic reflection model

[Tarik Rahman]

Hi there
I'm trying to implement the isotropic reflection model where
              [ exp(-tan^2(delta/alpha^2)]
 K =    -------------------------------------------------
            sqrt( cos(theta_i)*cos(theta_r) )*4pi*alpha^2

my diffuse is (0.2 0.2 0.2) and specular is 0.05 ( roughness = 0.05 ) so I get
the reflected colour as = diffuse/pi + spec*K and multiply this by the light
colour (1 1 1 )
and return it

my values are supposed to be around 0.106  but I always get either too big like
1.137 or too small like 0.0653.

Anyone have any idea where I might be going wrong, should I be doing some kind
of fall off factor where the light intensity at an intersection ( of a simple
plane) is inversely proportional to the distance from the light source.

Thanks for any help,

Tarik
--
Tarik Rahman
PhD student, Institue of Perception, Action and Behaviour
School of Informatics
University of Edinburgh