POV-Ray : Newsgroups : povray.general : photon problem: image of projected image_map is clipped at the corners : Re: photon problem: image of projected image_map is clipped at the corners Server Time
7 Dec 2022 09:31:09 EST (-0500)
  Re: photon problem: image of projected image_map is clipped at the corners  
From: Christian Froeschlin
Date: 22 Sep 2010 04:01:25
Message: <4c99b7d5$1@news.povray.org>
Corvin Zahn wrote:

> With photons the left and right bottom corners of the image will be clipped:

I can reproduce the problem under Windows XP using 3.7 beta 39.
It seems to look like the photon shooting simply stopped with
its outward spiraling even though the bounding box was not yet
covered. However, the problem persists when setting autostop to
1.0, enforcing a larger bounding box, or brutally increasing
the photon count. It also persists when replacing the polygon
with a box of some small thickness using ior 1.0.

I think it is a bug, although the photon FAQ mentions that
the photon method is not very well suited for planar objects
with an ior close to 1.0. You might wish to report this
under http://bugs.povray.org/.

As a workaround, splitting the slide object into strips
seems to help, although you may then need a higher photon
count to avoid artefacts:

union
{
   box {<0,0.0,0>, <1,0.1,0.01>}
   box {<0,0.1,0>, <1,0.2,0.01>}
   box {<0,0.2,0>, <1,0.3,0.01>}
   box {<0,0.3,0>, <1,0.4,0.01>}
   box {<0,0.4,0>, <1,0.5,0.01>}
   box {<0,0.5,0>, <1,0.6,0.01>}
   box {<0,0.6,0>, <1,0.7,0.01>}
   box {<0,0.7,0>, <1,0.8,0.01>}
   box {<0,0.8,0>, <1,0.9,0.01>}
   box {<0,0.9,0>, <1,1.0,0.01>}
   ...
}


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