POV-Ray : Newsgroups : povray.binaries.images : Questions about photons : Re: Questions about photons Server Time
16 Sep 2021 14:37:23 EDT (-0400)
  Re: Questions about photons  
From: Alain Martel
Date: 12 Sep 2021 12:43:23
Message: <613e2e2b$1@news.povray.org>
Le 2021-09-11 à 03:00, kurtz le pirate a écrit :
> On 06/09/2021 01:38, Alain Martel wrote:
> 
> 
>> In that scene, only the first mirror should be set as target. If there 
>> is a second target object in a location where no photon can reach it, 
>> then, the photons destined for that extra target are lost.
>> If you have two target, one behind the other, and even if the first 
>> target object is fully transparent, then, that first object will 
>> intercept and block all the photons shot at the second object.
> 
> Each  mirror as this settings :
> photons { target refraction off reflection on collect off }

The only relevant part is «collect off».

> 
> 
>> Also, does the projector object restrict the beam ? That's another 
>> thing that may cut down the number of photons shot.
> 
> No, the light source for the beam is out of the "projector".

Good.

> 
> 
>> Also, if you have a second light, each light will attempt to shot it's 
>> half of the requested photons. Any light_source that you don't want to 
>> shot photons absolutely need this photon block :
>> photons{reflection off refraction off}
> 
> I have an other light source. Kind of "global illumination" for the 
> scene. for her  setting is :
> photons { refraction off reflection off } media_interaction off

OK. This turn photons shooting off for that light.

> 
>> ALL light_source except the shadowless ones have this default photons 
>> block :
>> photons{reflection on refraction on}
> Yes, there is only one light source for the laser with
>     photons { refraction on reflection on }

That photons block is the default photons block. It's not required.

> 
> 
>> For the dimer part, it's probably related to the media used. Looks 
>> like you used type 5 with a negative eccentricity, probably between 
>> -0.25 and -0.5. Try using an isotropic scattering media.
>> Try using type 1 (isotropic) or 4 (Rayleigh).
>>
>>
> The global media is defined like this :
> box {
>   <32, 0, -1>, < -1, 6, 32> // 28>
>   hollow
>   texture { pigment { color rgbf 1 } }
>   interior {
>    media {
>     scattering {
>      1,
>      color White
>      extinction 0
>      }
>     method 2 // uniform
>     intervals 2
>     samples 4
>     }
>    }
>    photons { target }
>    }
> 
> 
> 

This is not correct : «photons { target }». This may be the reason you 
are missing about half your photons. The light_source is attempting to 
shoot half of the photons at the media box.

It should be «photons { pass_through }» if the light is outside the 
media box. No need for a photons block is the light is inside the media box.

Using method 2, you may not have enough intervals, or samples. This may 
cause the sampling to miss half of the beam. Try using intervals 3 or 4. 
OR, you may not have enough samples. Try samples 6, 7 or 8.

You may try method 3 instead, without the intervals statement, and 
increase samples to about 10 (default value for method 3).


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