[TowerTalk] RE: Downloading terrain data for use with HFTA

[W3YY]

To All -

 Thanks to Pete for posting this, as the process has, indeed, changed.

 I want to note a related observation.  I have very detailed local
 topographic maps of my property and the surrounding area.  These were
 obtained from my County.

 Using a GPS receiver I "located" my two towers, then downloaded the USGS
data, and ran elevation profiles.  Something seemed wrong.  When I checked
the USGS elevation at the base of each tower, the elevation figures didn't
seem right.  This conclusion was based on where I know the towers are
located relative to my property lines and my physical topo maps.  I suspect
the errors in the GPS are causing the problem, i.e., the location as
specified by the GPS receiver is not sufficiently accurate and might be off
by 25ft or more.

The topography on my property is quite irregular, so "moving" the towers
even 25 or 50 ft can make a noticeable difference in elevation and elevation
profiles.

The bottom line - if you are on highly irregular property, I'm not sure I
would trust results based on the USGS data.  This is not because the the
USGS data is bad, it's because you can't really determine the correct
position of your towers, unless you have a military-grade GPS unit.

Maybe there is another explanation.  Other thoughts are welcome.  I'd like
to be able to confidently use the USGS data, if possible.

 73, Bob - W3YY
>
>
> ----- Original Message ----- 
> From: "Pete Smith" <n4zr at contesting.com>
> To: <towertalk at contesting.com>; <antennaware at contesting.com>
> Sent: Wednesday, January 12, 2005 8:29 PM
> Subject: [TowerTalk] Downloading terrain data for use with HFTA
>
>
> > This is intended for anyone who has tried to download terrain data from
> > USGS to use with HFTA, only to discover that several aspects of the
> > downloading process have changed.  N6BV has just posted an article that
I
> > wrote on the ARRL web site,
> >
> > http://www.arrl.org/notes/9043/HFTA-Changes.pdf
> >
> > which gives the new procedure with screen shots and active links.  Both
> > Dean and Peter Guth, the author of MicroDEM, were a huge help in pulling
> > this together and making things work again.
> >
> > 73, Pete N4ZR
> > The World HF Contest Station Database
> > was updated 13 December 2004
> > 2843 contest stations at
> > www.pvrc.org/WCSD/WCSDsearch.htm
> >
> > _______________________________________________
> >
> > See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless
> Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with
any
> questions and ask for Sherman, W2FLA.
> >
> > _______________________________________________
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> > TowerTalk at contesting.com
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> >
>