High!

Once again I embarked on an attempt to build at least a crude version of 
Khyberspace... therefore, I downloaded the 93 SRTM data tiles covering 
Afghanistan (each one square degree at 1200 by 1200 measuring points), 
then used a geo-visualization software called "3DEM" to remove faulty 
radar samples (produced mostly by cloud cover), converted the exported 
ASCII terrain matrix files to 16-bit PNG heightfields via a PoV-Ray 
script (attached here) and then generated mesh2 objects following 
Earth's curvature from these PNG heightfields.

For performance reasons, I generated the mesh2 data as a (huge!) *.inc 
file rather than calculating them within the final scene script, using a 
separate PoV-Ray script ("mesh2writer.pov").

Before starting with Afghanistan (those tiles need some more intricate 
processing as they contain many error pixels), I tried a part of the 
world more accurately mapped by the SRTM Space Shuttle mission in 2000 - 
the part of Germany where I live, four one-square-degree tiles stitched 



When I rendered the scene for the first time, I found ugly gaps between 
the triangles of them mesh2 - and instantly I was reminded of my earlier 
attempt at terrain from SRTM tiles back in 2005, when the same occurred. 
Back then, IIRC it was Mike Williams who suggested rounding errors as 
the reason for the gaps, so I looked up my old PoV-Ray scripts to find 
out how I solved the problem...

Back then, I subtracted from each vertex of the mesh2 a vector 
consisting of a normalized direction vector according the the 
geographical positon of the vertex multiplied by Earth's radius. At the 
end of the mesh statement, I re-translated the whole thing back to its 
original position (see script file "png2mesh2.pov").

But when I now render the scene, I just get empty blackness... what went 
wrong?

See you in Khyberspace!

Yadgar

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