"trulayne" <tru### [at] newrrcom> wrote in message 
news:44469de3$1@news.povray.org...
>I am in the process of building a landscape.  I am using a USGS Dem image 
>for my heightfield. I there an easier way to determine the "y" value 
>knowing the "x" and "z" other than trial and error? Some objects are 
>fencelines built from spline curves. With the number of points needed for 
>these curves, the job becomes time intensive doing it by trial and error.
> Thanks in advance, Dennis

Hi Dennis,

You can use the 'trace' vector function to find a point on a surface. In 
this case you would use it to shoot a ray straight downwards to intercept 
the surface and return the coordinates of the point on the surface.

Alternatively I think you should be able to use the 'eval_pigment' 
predefined function on the image to pick up the color and work out the 
elevation from that.

Regards,
Chris B.

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