POV-Ray : Newsgroups : povray.general : Unwanted black spots in regular pattern : Re: Unwanted black spots in regular pattern Server Time: 16 Jun 2019 06:56:22 GMT
  Re: Unwanted black spots in regular pattern  
From: clipka
Date: 10 May 2019 12:50:33
Am 10.05.2019 um 13:22 schrieb Jasper:

> I am trying to introduce photometric data files of luminaires (i.e. IESNA .ies
> or EULUMDAT .ldt) in Povray to get "correct" lighting distributions. In order to
> do so, I combine
> 
> (1) a point light source
> (2) a sphere with radius 0.01 and spherical mapping of an image map (.png with
> the alpha channel used for transparency) which represents the lighting
> distribution for different angles.
> 
> My camera view is from above, simulating a satellite view (Z-direction is "up")
> and assuming a simple planar object in xy. While the above-mentioned method
> works in most cases, it seems that for large coordinates (e.g. 1 000 000
> translation of both camera and luminaire in the xy plane), it no longer does (it
> becomes a regular point source), and some black dots appear in the resulting
> image. The strange thing is that it is not the case for translations of, e.g.,
> 100 000.
> 
> Has anyone encountered similar problems and/or knows the reason for this?

It is generally a bad idea to place your scene far off-center. The 
reason is that POV-Ray uses floating-point mathematics, which can cover 
a wide range of values, but degrades in (absolute) precision as the 
magnitudes grow. So the further you place your objects away from the 
center, the more you invite artifacts from precision issues (think 
rounding errors).


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