Hi

I'm using a Digital Elevation Model,converted to a  POV 
heigthfield, to try to produce a more realistic simulation of a 
satellite image than simple shading. I've modified a little the 
following script which was used for other DEM work, however I 
am particularly interested in simulating the effects of changes in 
solar elevation (ie y value of the illuminator). If this angle is low 
then terrain undulations are crisply picked out. Greater than 
20degrees and they become virtually unidentifiable.

In general shaders (and the current script) are unable to cope 
with the low levels of ambient light and, I assume, a greater 
degree of diffusion. I have posted on my web site a couple of 
graphics; the first shows a "real" satellite image 
(http://www.geocities.com/Yosemite/Rapids/5855/satellite_im
age.jpg) which shows small linear landforms clearly depicted. 
The second 
(http://www.geocities.com/Yosemite/Rapids/5855/rendered.jp
g) shows my rendering so far (both using the same solar 
illumination angle). This is much darker however similar linear 
landforms are visible in the centre (although its a different area). 
Does anyone have any suggestions for simulating the results in 
the image??


Cheers

Mike

#include "shapes.inc"
#include "colors.inc"
#include "textures.inc"

camera {
   location <0.0, 1000.0, 0.0>
   //direction <0.0, 200, 4.0>   //4.0 for telephoto effect
   //up <0.0, 1.0, 0.0>        
   //right <4/3, 0.0, 0.0>
   look_at <0.0, 0.0, 0.0>
}

// Define a couple of colors for the light sources.
#declare MainLight = color red 0.9 green 0.6 blue 0.6;
#declare FillLight = color red 0.23 green 0.23 blue 0.25;

// Light source (main)
light_source { <300.0, 154.0, -300.0> White }
//light_source { <500.0, 300.0, 600.0> color FillLight }

height_field  {
   tga "d:\drumlindem.tga"    // x 0-1.0 y 0-1.0 z 0-1.0
   smooth
//   pigment { color red 0.3 green 0.59 blue 0.11 }
   pigment { color red 0.4 green 0.4 blue 0.4 }

 
   finish {
	  //crand 0.025         // dither  - not used often, but 
this image needs it. 
	  ambient 1.5         // Very dark shadows
	  diffuse 0.4         // Whiten the whites
	  //phong 0.1          // shiny
	  //phong_size 100.0    // with tight highlights
	  //specular 0.1
	  //roughness 0.6
	  //brilliance 5.0
   }
   
   translate <-0.5, 0.0, -0.5>  // Center the image by half  
   scale < 1200, 64.0, 1200 >  // scale horiz x 1200 and vert x 
64

}

// end of file

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