I've had limited success using the iso_surface and pigment function of Super
Patch to make a height field of a elevation map of the Earth and then
differenced it away with a inner sphere, the resulting animation was so-so.
I say limited only because the best topographical images I have here to do
this with are lacking in full globe coverage.  However, using Kens idea
would work okay for this same thing and cut away the oceans very well,
except use black instead.
Here's the generic pov script, less changes which might be needed:

#declare _C_ = .5; // clock

global_settings {
max_trace_level 6
 }

// pointlight and camera position
#declare LCX = 0;
#declare LCY = 1;
#declare LCZ = -9;

// light_source { <LCX+15,LCY+5,LCZ> color rgb <1.5,1.5,1.5>
// }
camera
{
  location  <LCX,LCY,LCZ>
  angle 22.5
  look_at   0
}

#declare Earth =
 function {
  pigment {
   image_map {
              gif "w_map_gt" // your image here
              map_type 1
             }
          }
 }

#declare Radius=1;
#declare Spheroid =
 function {"sphere",<Radius>}

difference {
 isosurface {
  function{Spheroid(x,y,z)-(Earth(x,y,z)/9)}
   method 2
   max_gradient 3
   bounded_by {sphere {0,1.1}}
   texture{
    pigment {rgbft<0,3,0,.33,.5>}
     finish {ambient 1.5 diffuse .9 phong .3 phong_size 30}
          }
  rotate -180*y rotate -_C_*360*y
}
 sphere {0,1.075-(.075*_C_) pigment {rgbft<3,0,0,.66,.66>} finish {ambient
3}}
}


Bob

Ken <tyl### [at] pacbellnet> wrote in message
news:382DA53C.3D5CE800@pacbell.net...
>
>
> Jon Lockhart wrote:
> >
> > I was watching a news show one day and they had a view of a
> > spinning globe. Each continent seemed to be created out of
> > a mesh of some kind. Where oceans normally, would be, you
> > could see through to the other side of globe. Each continent
> > was its own object. In other words, they weren't using an
> > image-mapped sphere. I've done image-mapped spheres.
>
> Hypothetical solution untested and untried -
>
> Going back to the image map idea for just a minute it might still be
> possible to use this method to create the model you want. The method
> I would use would be to paint the ocean basins white and leave the
> land masses the original colors. Then use a filter index for the
> image map that cooresponds to the white used in the ocean basins.
> When sphericaly mapped to a globe you should now see just the land
> masses with clear areas where the oceans once were.
>
> --
> Ken Tyler -  1200+ Povray, Graphics, 3D Rendering, and Raytracing Links:
> http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/

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