POV3.5 beta 7 on Win98.

I don't know if it's a bug, a forgotten feature or if it works as it has to.

The double_illuminate feature doesn't take into account
the indirect illumination (i.e. radiosity samples).

Try the code below:

// test double illuminate + radiosity
box{<-10,-10,20>,<10,10,21> pigment{rgb 2}finish{ambient 1}}
plane{z,0 pigment{rgb 1}finish{diffuse 1.2}
	hollow double_illuminate
}
camera{location -10*z look_at 0}
global_settings {
	max_trace_level 30
	adc_bailout 0.02
	radiosity{
		count 100
		nearest_count 4
		error_bound .5
		recursion_limit 1
		brightness 1.0
		
		pretrace_start  .05
		pretrace_end  .02
		
		low_error_factor .5
		gray_threshold 0.2
		minimum_reuse 0.015
		normal on
		
		max_sample 2.0
		adc_bailout .02
    }
}

The scene renders completely black.
If you put the camera on 10*z (outside of the plane),
you see that the plane is illuminated by the (very) white box.

Hope that it is possible (and easy) to implement.

Thanks for all.

Bouf.

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Bouf <tof### [at] orekacom> wrote:
> POV3.5 beta 7 on Win98.
>
> I don't know if it's a bug, a forgotten feature or if it works as it has to.
>
> The double_illuminate feature doesn't take into account
> the indirect illumination (i.e. radiosity samples).
>
> Try the code below:
>
> // test double illuminate + radiosity
> box{<-10,-10,20>,<10,10,21> pigment{rgb 2}finish{ambient 1}}
> plane{z,0 pigment{rgb 1}finish{diffuse 1.2}
>  hollow double_illuminate
> }
> camera{location -10*z look_at 0}
> global_settings {
>  max_trace_level 30
>  adc_bailout 0.02
>  radiosity{
>   count 100
>   nearest_count 4
>   error_bound .5
>   recursion_limit 1
>   brightness 1.0
>
>   pretrace_start  .05
>   pretrace_end  .02
>
>   low_error_factor .5
>   gray_threshold 0.2
>   minimum_reuse 0.015
>   normal on
>
>   max_sample 2.0
>   adc_bailout .02
>     }
> }
>
> The scene renders completely black.
> If you put the camera on 10*z (outside of the plane),
> you see that the plane is illuminated by the (very) white box.
>
> Hope that it is possible (and easy) to implement.
>
> Thanks for all.
>
> Bouf.

I am wondering if this problem is solved? I am using double_illuminate scene and
found that the reflectance of the scene is underestimated (version 3.7.1).
Thanks in advance.

Post a reply to this message

>
> I am wondering if this problem is solved? I am using double_illuminate scene and
> found that the reflectance of the scene is underestimated (version 3.7.1).
> Thanks in advance.
>
>

double_illuminate is not physically acurate.
Instead, I recomend using the new, as of version 3.7.0, back side 
illumination. It's activated by adding a second value for diffuse as follow:
diffuse 0.5, 0.4

In this case, 50% of the incomming light is diffused from the front side 
and 40% is diffused through the surface to the back side. Front and back 
been relative to where the light is comming from.

Back side illumination is fully compatible with radiosity.
It allow precise controll over the transmitted part of the incident light.
Care should be made to ensure that the sum of the two components add to 
less than one if you want to get physically acurate, or at least 
plausible, results.

Post a reply to this message

Alain <kua### [at] videotronca> wrote:

>
> >
> > I am wondering if this problem is solved? I am using double_illuminate scene and
> > found that the reflectance of the scene is underestimated (version 3.7.1).
> > Thanks in advance.
> >
> >
>
> double_illuminate is not physically acurate.
> Instead, I recomend using the new, as of version 3.7.0, back side
> illumination. It's activated by adding a second value for diffuse as follow:
> diffuse 0.5, 0.4
>
> In this case, 50% of the incomming light is diffused from the front side
> and 40% is diffused through the surface to the back side. Front and back
> been relative to where the light is comming from.
>
> Back side illumination is fully compatible with radiosity.
> It allow precise controll over the transmitted part of the incident light.
> Care should be made to ensure that the sum of the two components add to
> less than one if you want to get physically acurate, or at least
> plausible, results.

Thanks. I tested the back side illumination with radiosity. I am rendering a
scene with very dense leaves. The objective is to get the physically accurate
illuminace of each pixel. I set the assumed_gamma and file_gamma as 1.0. Then
this the pixel color is supposed proportional to the illuminace? However, it
seems the light does not propagate deep enough into the canopy (with radiosity
and side diffused light). When compared with the reference results achieved with
Monte Carlo method, the illuminace or reflectance is underestimated. I am
wondering this is because Pov-ray ignore some physical processes or I did not
set the right functions. Thanks again.

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Since this discussion goes into a direction unrelated to beta testing, I
would suggest to continue the discussion in the "Reflectance of 3D
canopy" thread on povray.general.

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