In article <402891e8$1@news.povray.org>,
 "Maurya Shah" <mau### [at] hotmailcom> wrote:

> I have been using the "Turbulence" function to add noise to the color in the
> media. But as we know turbulence is coherent in space. But to generate a
> sequence of renderings (e.g. an explosion cloud evolving in time) a noise
> function needs to be temporally coherent. Otherwise, if the same noise is
> applied to a point at all the steps in time, then the animation will have
> the classical "shower curtain effect" cited in literature. So, can anyone
> please suggest if there is a way to generate such a noise in POVRAY,
> somethings that looks spatially as well as temporally coherent?

I'm not familiar with the "shower curtain" effect. However, noise is 
temporally coherent in that it is constant and deterministic, you always 
get the same results for a given 3D point. It sounds like what you want 
is a 4D pattern, a noise function that varies smoothly with time. This 
is possible, I even once saw a recursive implementation of Perlin noise 
that could handle any number of dimensions, but slower to compute and 
more complex, and I don't know if it has been done in POV.

If your use of the pattern is constrained to two dimensions, a floor 
plane for example, then you can just move the pattern along the 
remaining dimension. Or you could combine several noise functions in 
various ways, and translate them in different directions.

-- 
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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