Tim Nikias v2.0 wrote:

>> If I want caustics on a surface BELOW a photon target, must the surface
> that
>> the photon target is on also be a photon target?
>>
>> I have tried many combinations but simply cannot get caustics on a
>> surface "behind" a photon target, even with very small spacings and lots
>> of
> photons
>> - all my photon caustics stay confined to the glass object. I simply
> cannot
>> get caustics onto the table "behind" the glass standing on it.
> 
> Can you provide small, minimal sample scene (post it on
> povray.binaries.scene-files), so that I could have a look at it? You could
> also try to put both objects in a union and shoot photons at the union,
> but that's just a random guess, nothing based on experience or such.
> 

Hi Tim!

Thanks for replying to my post - I think I have at least demystified it for
myself a bit. I made the following test scene:

global_settings
{
        adc_bailout 0.05
        max_trace_level 10
        
        photons
        {
                spacing 0.01
                jitter 0.15
                max_trace_level 10
                adc_bailout 0.05
                autostop 0
                radius ,1.75
                
                //save_file "phottest.pht"
        }
        
}

camera
{
        location <0,0,5>
        look_at <0,2,0>
}

light_source
{
        <4,4,5>
        color rgb <1,1,1>*2

        photons
        {
                refraction on
                reflection on
        }
}

box
{
        <-1,-1,-1>
        <1,1,1>
        material
        {
                texture
                {
                        pigment
                        {
                                color rgb <1,0,0>
                        }
                }
        }

        scale <2,2,1>
        
}

cylinder
{
        <-1,-1,-1>,
        <-1,1,2>
        0.25

        material
        {
                texture
                {
                        pigment
                        {
                                color rgbft <0,0,1,0.3,0.65>
                        }

                        finish
                        {
                                diffuse 0.55
                                ambient 0.45
                                specular 0.9
                                roughness 0.2
                                metallic 0.25
                                reflection 0.25
                        }
                }

                interior
                {
                        ior 1.3
                        dispersion 1.4
                        dispersion_samples 10
                        caustics 2
                }
        }

        translate <1,0,0>

        photons
        {
                target 0.75
                reflection on
                refraction on
        }       
}

This works ok. However in my scene I am working on (a bit too big to post),
specifying the object like this (I copied exactly the same ior, texture,
and shape) makes it turn absolutely 255,255,255 white - I have one very
distant (1000 units away) light. Specifying "collect off" in the glass
object's statement makes its texture be okay, but I guess THIS is why it
does not leave caustics on the surface it is standing on.

Any idea how I can prevent the photon object being "white out"-ed when I
remove "collect off"? Obviously I am making some mistake and specifying
"collect off" makes the class NOT leave caustics like I want it to.

Thanks!

-- 
Stefan Viljoen
Software Support Technician
Polar Design Solutions

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