I am trying to overlay a chorpleth map (i.e., a map showing country borders
with shaded values) onto a height field. Both are 24 bit tga images and
both have exactly the same size and geographic extent. I can create a
height field no problem, but any image I place on top of it doesn't display
correctly. What I normally end up getting is only the highest points of the
height_field getting some color from the overlaid image, but even that
color is not correct.

It is important that the image is aligned perfectly with the height_field in
order to match country borders with physical features, particularly
coastlines.

This seem like an easy process of just overlaying an image onto a
height_field, but maybe I am missing something. Below is one sample of some
code I have tried.

height_field {
  tga "d:/povcyg/scenes/gtopo30/dtm.tga"
      pigment {
  image_map{ tga "d:/povcyg/scenes/gtopo30/map.tga"
  map_type 0
  interpolate 2
   }
  translate <-.52, 0, -.5>
     scale <100, .5, 100>
  }
     translate <-.52, 0, -.5>
     scale <100, .5, 100>
    }

Any help would be greatly appreciated.  Thanks

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