[aprssig] 'view sheds' ? topo data

[K. Mark Caviezel]

by the by, before everyone starts clamoring for 'where
to get the topo data?' it's worth saying that the
topographic data from the Shuttle Radar Topography
data is freely available from NASA in 1 arc second and
3 arcsecond flavors.    A 'square degree' in 1-arc
second resolution is about 25 megs unzipped.   It's
worth noting that that shuttle mission was flown in
the winter, I think standing water spoofed the radar. 
The lakebed of the 4000 foot altitude black rock
desert 'playa' has some holes in it the register as 0
feet elevation.   Those holes equate to the lowest
ground, standing water on it probably absorbed or
completely reflected the radar pulses with no back
scatter.   These holes in the data are obvious for
elevated terrain, lower elevation data maybe not as
obvious. 

- KMC ng0x