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| GeoCommunity Mailing List |
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| Mailing List Archives |
| Subject: | Re: [gislist] GPS systems (2nd time) |
| Date: |
06/08/2005 03:30:03 PM |
| From: |
Garrie Rouse |
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One other thing you will want to consider is the environment in which you
plan to operate the GPS. If you plan to map within hardwood forests, then
you will have a harder time seeing the satellites. And, even if you are
successful at that, there is still the problem of multi-path (bounced
signals from the satellites off the trees) which can give you erroneous
solutions. Read the fine print ... "submeter" only applies when you are NOT
in a multi-path environment. For the former problem I would recommend an
external antenna. In fact, for Trimble products and the like, you can get a
2m staff (after market product) to attach the external antenna to (instead
of having it positioned off your back) and get a bracket (also an
aftermarket product) that allows you to attach your data logger to the same
staff. This allows you to not only get your antenna higher within the
understory, but also gives you greater precision in positioning and holding
the antenna in one place after you get a lock on 4 or more satellites. For
the problem of multi-path ... well, there are not a whole lot of solutions
shorts of collecting many more readings over a longer time period to average
your position.
Garrie Rouse
Rouse Environmental Services, Inc.
PO Box 146
Aylett, Virginia 23009
Phone: (804)769-0846
Fax: (804)769-0347
----- Original Message -----
From: "Brian Russo" <brian@russo-associates.com>
To: "Neil Havermale" <neilh@redhensystems.com>
Cc: <gislist@lists.thinkburst.com>
Sent: Wednesday, June 08, 2005 9:50 AM
Subject: Re: [gislist] GPS systems (2nd time)
>
>
> Neil Havermale wrote:
> > Bader -
> >
> > There are two aspects of your accuracy quest: the GPS receiver and its
level
> > of smarts and second, your source of differential corrections.
Differential
> > corrections are a supplement to the GPS system and while not a GPS
timing
> > signal itself, the RTCM-105 standard correction passes fine-tuning
aspects
> > for each satellite in view. The differential corrections remain key to
> > accuracies under 10 meters these days. If you can get the "free"
> > differentials from the WAAS (North America) or SBAS (Europe) satellites,
> > under $300 handhelds like Garmins (http://www.garmin.com) will deliver
1.5
> > meter accuracy 67 percent of the time. These free corrections are not
> > available everywhere.
> >
> > For just about anywhere on the planet your can replace free with
commercial
> > differential corrections like Omnistar (http://www.omnistar.com
receiver
> > with annual subscription $800+yr1) and you might get 1.2 meters out of
the
> > same Garmin - but this integration is not really a handheld solution any
> > more. Put the most accurate Omnistar correction on a high-end Trimble
or
> > Thales handheld/PDA ($3500+) who's' built-in GPS engines know how to
deal
> > with "carrier surfing" or "carrier smoothing", you'll gain 0.5 meters
say 95
> > percent of the time when in good conditions.
>
> Do you know if they simply implement Kalman filters or similar?
>
> Strongly agree with everything else, more emphasis that you'll need
> someone who actually knows how to use this (technique > equipment).
>
> - bri
>
> >
> > http://www.trimble.com/pathfinderproxh.shtml
> >
> > http://www.thalesnavigation.com/en/index_flash.asp
> >
> > Thales, Garmin and Trimble represent high accuracy integrated GPS,
hardened
> > WinCE forms with daylight readable screens, a CPU and memory to handle
PDA
> > GIS tools like ArcPAD, EzMAP, and MapX Mobile.
> >
> > To achieve a one meter accuracy say 50 percent of the time you'll need
to
> > consider a professional GPS system investment. Gaining accuracy to
within a
> > meter essentially all of the time will require a professional and well
tuned
> > system.
> >
> > FWIW
> > MidNight Mapper
> > Aka neil
> >
> > -----Original Message-----
> > From: bader nader [mailto:gis_man2002@yahoo.com]
> > Sent: Tuesday, May 31, 2005 7:23 AM
> > To: gislist@lists.geocomm.com: arcgis@lists.directionsmag.com:
> > esri-l@esri.com
> > Subject: [gislist] GPS systems (2nd time)
> >
> >
> > Hi all
> >
> > I have posted before that I'm planning to buy a GPS system , really I'm
> > confused ...
> >
> > When I do a search I found a lot of GPS...
> >
> > really I need some one who has a good experience in that and he used it
.
> > Since when I buy it no way to bring it back or to buy another.
> >
> > we are looking for h
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