Pat's point is correct regarding DGPS accuracy. To clarify, DGPS is
accurate to something
less than a meter in the horizontal and about 3x that accuracy in the
vertical depending on
the length of the "base line" or the distance from the differential
reference source. Satellite
L-band differential corrections provide about the same accuracy as the
free, government
sponsored corrections. Satellite corrections are available on a
subscription basis and are often
the only choice of DGPS corrections where no government signals are
available.
To achieve "survey grade" accuracies, Real Time Kinemetic (RTK)
technology must be
applied. This technology provides 1cm horizontal and 2 to 3 cm vertical
accuracy. It involves
a RTK base station at a known point and a "rover" unit that performs the
land survey. The
two units communicate over a high speed radio network providing the
"rover" with
corrections to it's position. The technology is becoming VERY accurate
but is still a bit
pricey. The latest receiver technology offers 20 mm accuracy, 20 msec
latency and updates
at 20 Hz, (20x/second!), in REAL TIME! 3 years ago you couldn't get that
sort of accuracy
even with post processed survey data!
There are a lot of conceptions regarding GPS and what it can and can't
do. The technology
is racing ahead and achieving it's promise at a blinding pace. For a good
tutorial and more
than you ever wanted to know about the subject, point your browser to
http://www.trimble.com and look around. One of the best tutorials
available.
73 de Jon...K6EL
K6EL@JUNO.COM
On Tue, 22 Dec 1998 12:50:06 -0800 (PST) Pat Barthelow <aa6eg@hh.tmx.com>
writes:
>
>Hi Dave,
>
>Gee...word travels fast on email....Unfortunately, TOPO only draws
>the
>profile plots and you have to pick off the elevations and distances
>from
>the plots..and enter your own ascii file ..great idea...someone
>should
>call the Topo makers, and ask
>them to also provide, in their next version, an ascii file of the
>profiles....My guess is that you can buy it at better
>outdoor/camping/hunting supply stores
> Also, there was a mention elsewhere on the reflector, of
>using
>DGPS for acquiring data points for plotting profiles....Even
>Differential
>((D GPS), which provides higher accuracy than raw GPS,) probably will
>not
>provide the accuracy you need to for terrain
>profiles used in antenna modelling...especially the elevation
>readings,
>which are quite innacurate unless sophisticated equipment is
>used....
>
>73, DX, de Pat, AA6EG/N6IJ;
>aa6eg@hh.tmx.com
>
>599 DX Drive, Marina CA 93933
>"The Contest Station from the Government"
>
>On Tue, 22 Dec 1998, Dave D'Epagnier wrote:
>
>> Hi pat,
>> say... do you know what type of ground profiles Topo generates? Is
>in
>> the format that TA or YT can read? Also, where can I buy Topo?
>>
>> thanks,
>> Dave
>>
>> > ----------
>> > From: Pat Barthelow[SMTP:aa6eg@hh.tmx.com]
>> > Sent: Tuesday, December 22, 1998 1:27 PM
>> > To: T A RUSSELL
>> > Cc: TOWERTALK@contesting.com
>> > Subject: Re: [TowerTalk] Measuring Terrain Slope /
>Elevation
>> >
>> >
>> > HI Tom,
>> >
>> >
>> > Sure...
>> >
>> > Get the software Map Program called "Topo". A CD ROM disk
>covering
>> > your
>> > area has the USGS Maps within, and the capability to generate
>ground
>> > profiles for you, using your inputs as to point of origin, and
>> > azimuth
>> > therefrom.....a great, cheap program....It also gives realtime
>> > azimuths,
>> > distances, bearings, Lat-Longs, and elevations, as you move the
>cursor
>> > around on your selected map.
>> >
>> > 73, DX, de Pat, AA6EG/N6IJ;
>> > aa6eg@hh.tmx.com
>> >
>> > 599 DX Drive, Marina CA 93933
>> > "The Contest Station from the Government"
>> >
>> > On Tue, 22 Dec 1998, T A RUSSELL wrote:
>> >
>> > >
>> > > Fellow Towertalkians:
>> > >
>> > > I would like to create a more accurate terrain profile in front
>of
>> > some
>> > > of my antennas for say 500 to 1000 ft out, every 50 ft.
>> > >
>> > > Other than using a transit, are there some simple methods for
>> > > determining slope or changes in elevation?
>> > >
>> > > Thanks for any clever ideas.
>> > >
>> > > Merry Christmas to all,
>> > >
>> > > Tom N4KG
>> > >
>> > >
>> > >
>___________________________________________________________________
>> > > You don't need to buy Internet access to use free Internet
>e-mail.
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>> > >
>> > > --
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>> > >
>> >
>> >
>> > --
>> > FAQ on WWW:
>http://www.contesting.com/towertalkfaq.html
>> > Submissions: towertalk@contesting.com
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>> >
>>
>
>
>--
>FAQ on WWW: http://www.contesting.com/towertalkfaq.html
>Submissions: towertalk@contesting.com
>Administrative requests: towertalk-REQUEST@contesting.com
>Problems: owner-towertalk@contesting.com
>Search: http://www.contesting.com/km9p/search.htm
>
>
73 de Jon...K6EL
K6EL@JUNO.COM
___________________________________________________________________
You don't need to buy Internet access to use free Internet e-mail.
Get completely free e-mail from Juno at http://www.juno.com/getjuno.html
or call Juno at (800) 654-JUNO [654-5866]
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
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