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[aprssig] Re: APRSpoint and other map sources

Stephen H. Smith WA8LMF2 at aol.com
Thu Dec 2 21:05:36 UTC 2004


KC2MMi wrote on 12/2/2004, 12:01 PM:

 > I like USGS mapping. I wish there was a $50 APRS solution that fully
 > implemented APRS, and included a full USGS topo map set.

The basic problem is that electronic versions of USGS  topo maps are 
bitmaps (scans of paper maps), not vector images.  The resulting bulk is 
absolutely enormous.

For example, look at Delorme's "3D Topo Quads" which are actual high-res 
images of USGS paper topo maps, overlaid with Delorme's more current 
vector road data borrowed from Street Atlas.  It takes 13 CD-ROMS just 
to cover California!    Because of the bulk, they actually sell the set 
for the northern and southern halves of California as separate products.

Delorme's own TopoUSA! uses the USGS raw terrain database (the so-called 
DEMs - Digital Elevation Models) repackaged into a proprietary 
compressed file format. [DEMs consist of millions of triplets of numbers 
(lat,long,elevation) for points every 3 or 30 seconds of arc across the 
U.S.]  TopoUSA uses this data to generate maps that look very similar to 
standard topos (brown contour lines, green patches for lowlands, 
outlines of urban extents, etc.) from the raw data. It can also render 
them in raised-relief-looking 3D.  This non-bitmap (i.e. quasi-vector) 
way of storing the data for the map images allow the relief data for the 
entire US to be stored on only 6 CD-ROMs.

Im my opinion, this is the program that should be mated with an APRS 
application.  Since the current editions of Delorme Street Atlas appear 
to use the same interface and presentation engine, discovering how to 
interface to TopoUSA would probably make Street Atlas usable as well.


Currently, one could save bitmap map images from either program, at any 
zoom level, with two lat/long points marked, calibrate them, and use 
them as static bitmaps in UI-View, Xastir, etc.


Stephen H. Smith                wa8lmf (at) aol.com

Home Page:                      http://wa8lmf.com

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