hughes, b. wrote:
>It can be frustrating, even if you set it up as right as seems necessary,
>when you see one scene file do what you can't get POV to do yourself.
>
>Main things you have wrong is the lack of a photons block in the mirror
>object and too low samples in the media. I removed the photons block from
>the media container since that isn't needed (apparently). So basically what
>I did is add:
>
>  photons {
>   target
>   reflection on
>   collect off
>   }
>
>and used intervals 4 samples 40,80. Which still wasn't enough really, and it
>is already very slow. I realize intervals is supposed to be on auotpilot
>whhen method 3 is used but it seems to help setting it and keeping samples
>lower. Otherwise I was having to go real high on the samples (100 or more).
>Oh, and I also went with a spacing 0.02; since I never use count in the
>global photons block I don't know it as well.

Thanks for looking at it. I don't understand why these sorts of changes are
needed when the optics.pov doesn't have them!

After reading through the help pages on photons a few (more) times, I
figured out the optics.pov scene uses the block object as the initial
target to shoot the photons at (since POV needs at least one target for the
photons...) and since it has a pair of holes the photons can move through
the holes and form the caustics in the media.

I made the changes you mentioned, but left the photon count as it was. This
gave an interesting string of pearls media effect along the reflected
photon vector which I am guessing is due to the low sample intervals (so
how does optics do it with an interval of 1??? - maybe its due to the
adaptive sampling type).

I then found that by making the media box more tightly fit the region around
the mirror, the scene traced _much_ faster (>10x the speed) and no longer
gave the string of pearls effect, instead I got a continuous reflected
beam! Oddly though, it seems that the effect just wont work if the light
source emitting the photons is not positioned within the media box (the one
in optics.pov is not!) I can't work this one out, it's as if the sides of
the media box are somehow opaque to the photons...

Even more strange (!), is I can use no_image and no_reflection to make the
mirror almost completely disappear, except for its casting a shadow, but
adding no_shadow stops the photons from working!

<Hopefully I haven't just run into some POVRay bugs...>

Thanks again,

Raymond.

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