Hi,

I try to understand how RADIANCE calculate the radiance values, but the specular value for one reflection isn't clear.

I understand, that the diffuse value is independent of view. On point P_r=(0 1 1) I got from rtrace for the red channel 0.22361, I calculated:

R_r_light=100

sphere_radius=0.5

distance=2.2360

rho_surf1=0.1

cos(63,43) = light incoming angle

R_r(0,1,1) = R_r_light * (sphere_radius)² / (distance)² * cos (63,43) * rho_surf1 = 0.223606797.

Ok, this value is fine, but what will happen if I look from (0 -1 1) to (0 1 -1) at point (0, 0, 0), I thought this, but it didn't work:

distance=3

rho_mirr=0.3

diff=0.9

spec=0.1

cos(45) = reflected light - observer angle

P_r=0.22361

R_r(0,0,0) = R_r_light * (sphere_radius)² / (distance)² * rho_mirr * diff + spec * P_r * cos(45) = 0.765811388

rtrace = 0.76517

Can somebody explain how the specular component is calculated on my test scene? I do not get it...

Here is my test scene:

######materials.rad######

void plastic mirr

0

5 .3 .2 .1 0.1 0

void plastic surf1

0

5 .1 .1 .1 0 0

void light lighty20

0

3 100 150 200

######test.rad######

mirr polygon plate1

0

12

-1 -1 0

1 -1 0

1 1 0

-1 1 0

surf1 polygon plate2

0

12

-1 1 0

-1 1 3

1 1 3

1 1 0

lighty20 sphere light_s

0

4 0 0 3 0.5