Understood. Thanks again.
It was another one of those 2-sided mind-twisters to me before. Had to
be sure.
One of these things in need of a graphical example perhaps, like:

           .
        .  =  .
     .  = ... =  .
   .  = ..+:+.. =  .
  .  = ..+:::+.. =  .
 .  = ..+:::::+.. =  .   // . is density
  .  = ..+:::+.. =  .    // + is first gather (or *only* gather)
   .  = ..+:+.. =  .     // = is second step and so on
     .  = ... =  .
        .  =  .
           .

Where basically the 'gather' is finding less further away.
I haven't a clue as to what you've made it actually do, just throwing
out an example of how it might be portrayed visually here.
Wonder how messed up this ascII art gets in different fonts. Oh well.


Nathan Kopp wrote:
> 
> You've got the density thing right.  Smaller value for density means smaller
> distance between photons that are shot means more photons.
> 
> Now, once you have photons depostited on the surface, you need to gather
> them.  To speed up the search for photons, you look only in an area close to
> the intersection.  The algorithm will need to process all photons within
> the radius you specify, so if you use something too big, it will take a
> long time to render.  However, if you choose something too small, the
> scene will look splotchy, since you won't get enough photons.
> 
> (It doesn't really process all photons withing the specified radius, but
> it will process a large number of them.)
> 
> You want to gather at least 20 photons (30+ is probably better)... so if you
> estimate that there are 30 photons in a circle with radius 0.1, you should
> set your gather radius to 0.1.
> 
> If you use something like this,
>   gather 20,100
>   raidus 0.1, 2, 0.1
> 
> then it will gather first using a radius of 0.1.  Then, if it fails to get 20
> (the minimum number specified), then it will increase the search radius by
> 0.1 (third parameter for the radius keyword).  It will do at most 2 searches
> (second parameter for the radius keyword).
> 
> This adaptive search radius is done because there will be some areas of high
> density and some areas of low density in most scenes, and this provides
> a good way to quickly render both with good image quality.
> 
> -Nathan
> 

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