Hi,

Many years ago I had said that I would write something to read GTOPO30[1] 
data and plot it using Ballon 3D.  GTOPO30 is a digital elevation model
of the earth to a precision of 30 arc secs, ie, about 1 km.   Think terrain.

This didn't happen at the time for assorted reasons[2].

Now, inspried by the International Digital Earth 3-D Visualization Challenge [3]
I've gotten something to start to work though I'm using the srtm30[4] plus data
rather than GTOPO30.  The data has the same format, but, a shuttle experiment
removed a lot of errors from the GTOPO30 data, and, the San Diego folks
added underseas topography as well.  

You can get the changeset for 3.6 from here [5] and more background
about what I'm shooting for here[6].  You'll also need to download 
either GTOPO30 or SRTM30 data to cover the area of the world you want
to plot. 

This should load and run in 3.6, and, with luck, on newer versions. 
You will obviously need Ballon 3D for this to even begin to work.
I'll make this work on newer versions sometime, if it doesn't already, 
but not for a month or so.

Some of this is kind of grotty.  The data reading interface is ugly and 
limited with too many things hard coded.  We also don't display too big an 
area since I want this to actually work even on old slow systems.

Thanks to Boris Gaertner (Boris.Gaertner at gmx.net) for his Ballon 3D tutorial
and very clear examples.  I'd probably still be banging my head on the 
keyboard without these examples.

cheers

bruce

[1] http://edc.usgs.gov/products/elevation/gtopo30/gtopo30.html
[2] Possibly the fact that my squeak system at the time was a 
33mhz 68k without FPU might have slowed me down.
[3] http://dex.telascience.org/entry-form
[4] http://topex.ucsd.edu/WWW_html/srtm30_plus.html
[5] http://www.pckswarms.ch/EarthSwarms/earthSwarms.4.cs
[6] http://www.pckswarms.ch/EarthSwarms.html