Wasn't it How Camp who wrote:
>Back in 2000, Warp posted an interesting isosurface pigment to help someone
>asking about contour maps:
>
>http://news.povray.org/povray.advanced-users/thread/<3A2CEC7C.83FC2739@
>psu.edu>/
>
>I've modified the code slightly, and am attempting to do something simple (I
>think).  I'd like to create a contour pigment that can be applied to either an
>isosurface (with results similar to Warp's) or to a plane where the contour
>lines match up with the 3D gradient pattern.
>
>I'm having trouble understanding how to correctly implement a non-gradient
>pigment that can be applied to either the isosurface or the plane.  Surely I'm
>making this way harder than it really is...?

Are you trying to do anything remotely like this?

http://www.econym.demon.co.uk/isotut/isobars.htm

The code for that is

#declare F=function{f_noise3d(x/6,y/5,z/5)}

plane {
  z, 0
  pigment { function{F(x,y,0)}
    colour_map {
     [0.2 rgb 4][0.2 rgb 0][0.204 rgb 0][0.204 rgb 4]
     [0.3 rgb 4][0.3 rgb 0][0.304 rgb 0][0.304 rgb 4]
     [0.4 rgb 4][0.4 rgb 0][0.404 rgb 0][0.404 rgb 4]
     [0.5 rgb 4][0.5 rgb 0][0.504 rgb 0][0.504 rgb 4]
     [0.6 rgb 4][0.6 rgb 0][0.604 rgb 0][0.604 rgb 4]
     [0.7 rgb 4][0.7 rgb 0][0.704 rgb 0][0.704 rgb 4]
     }
  }
}

-- 
Mike Williams
Gentleman of Leisure

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