In article <4018e074@news.povray.org>,
 "Felbrigg" <som### [at] microsoftcom> wrote:

> I'm working on a scene that has two isosurfaces ( hills and water ) but
> where they meet I'm getting a line of artifacts.  I've included a much
> simplified version of the scene below in the hope that someone can throw
> some light on the matter for me.  Note : one of the isosurfaces has a
> "Clear" pigment, so you wont see it when it renders, but you will see the
> line of artifacts.  This "clear" isosuface must remain clear as it will
> eventually be water.

You're using the default accuracy, which is low enough that POV gets 
confused when it tries to find the right intersections. At the points 
where the artifacts show up, the green isosurface is just too close to 
the clear one for the solver to work reliably...sometimes the clear one 
is hit first, when it is actually behind the green isosurface, in which 
case the transmitted ray goes off to nowhere. Also, intersections too 
close to the start point of the ray are ignored, to avoid problems where 
rays reflecting off of or refracting through an object immediately hit 
it again due to precision errors. Putting "accuracy 0.0001" in both 
isosurfaces fixed the problem, though rendering will be slower. Higher 
resolution renders may need more accuracy. Antialiasing will help to 
soften or eliminate the artifacts, as well, especially scattered 
single-pixel "dust".

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: <chr### [at] tagpovrayorg>
http://tag.povray.org/

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