[aprssig] Re: APRSpoint and other map sources

Gerry Creager N5JXS gerry.creager at tamu.edu
Thu Dec 2 23:33:52 EST 2004

So: Do we need to consider the 1:100K topo's as an interim solution?


Curt, WE7U wrote:
> On Thu, 2 Dec 2004, Stephen H. Smith wrote:
>>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.
> Mostly true.  There are also SDTS-format versions of the DLG topo
> contours.  Those are vector contours.  Xastir can overlay those on
> top of other maps.  See http://www.xastir.org, Search and Rescue
> Features link (on the left) for an example of what that looks like.
>>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.
> We have the possibility of supporting DEM's with Xastir in the
> future.  The map library that supports this isn't fully integrated
> into Xastir yet.  When it is, we'll have some fun with that stuff
> too.  I doubt I'd be interested in any topo info that could be
> stored on 6 CDROM's, as the detail just isn't there for my purposes.
> Nice to look at though.
> What I'd like to see is a repository for the SDTS contour files,
> downloaded off the USGS site onto some other server.  Same for any
> USGS geoTIFF topo images.  If we had them all available in one spot
> and organized nicely, it'd help a large number of people that are
> having trouble getting the ones they need.  The SDTS files are not
> supposed to be available for free forever.  They're just there now
> to drum up interest in the SDTS format.  All of that data was payed
> for by U.S. taxpayers and is free for use, so creating our own
> download server is just fine.
> I have all of the topos for WA, and some for OR/ID/MT/HI.  I could
> certainly try to upload a few of them if we had space for them.
> Another problem is that state download sites for geoTIFF topo maps
> often trim the borders, and convert them to a proprietary format
> called MrSID, instead of the open geoTIFF format.  This makes them
> harder to use in the future.  If we had a download server for the
> original files we could extend their usefulness.
> Perhaps one of the distributed servers that is always making the
> news (for bad reasons) could be used for this sort of thing nicely.
> Bittorrent perhaps?  Anyone know more about this sort of thing?
> --
> Curt, WE7U.   APRS Client Comparisons: http://www.eskimo.com/~archer
> "Lotto:    A tax on people who are bad at math." -- unknown
> "Windows:  Microsoft's tax on computer illiterates." -- WE7U
> "The world DOES revolve around me:  I picked the coordinate system!"
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Gerry Creager -- gerry.creager at tamu.edu
Texas Mesonet -- AATLT, Texas A&M University	
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