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| Subject: | Re: [gislist] GPS systems (2nd time) |
| Date: |
05/31/2005 08:20:01 PM |
| From: |
Neil Havermale |
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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.
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 handy one with one meter or less accuracy (in the middle
east), handy (IPAQ, tablet PC), something like build in or Card.
another Question whether the existence of the external antenna will make big
effect.
Hope that some will help me...
Regards,
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