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| Subject: | GISList: SUM: GPS receiver recommendations |
| Date: |
05/29/2003 04:10:01 PM |
| From: |
John Callahan |
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Thanks to everyone who sent me their experiences and recommendations
concerning GPS receivers. I received nearly three dozen email responses
and a half dozen phone calls! It is difficult to summarize all of the
relevant information, including what I read on some websites, but I will
do my best...
Original Question:
-------------------
I am seeking recommendations for purchasing 2-4 GPS receivers, which I
hope to purchase in the near future. Who are the other main
suppliers/manufacturers? My target price range is less than $500 but I
can go up to $1000 if that's what I need. Accuracy should be 5 meters
or better. DGPS compatibility is preferable. Ruggedized is not
necessary. The units should also be compatible with Windows 2K/XP
operating systems for direct uplink as well as with ESRI products. Any
advice you can give me would be greatly appreciated.
Summary of Responses:
-----------------------
Differential GPS was highly recommended and required to increase the
standard GPS accuracy (10 - 15 meters) to 5 meters or better. Using the
DGPS signals from the US Coast Guard marine beacon stations, accuracy
increases to 3 - 5 meters. (For Delaware folk, there is a nearby beacon
at Reedy Point, Delaware.) Wide Area Augmentation System (WAAS), a
form of DGPS, is satellite based and can be used anywhere in the
country. WAAS capability will increase the accuracy to 3 meters or
better but you need a clear view of the southern sky since the WAAS
satellites are geostationary (and an external antenna may be necessary
depending on your environment.)
More advanced and expensive (typically $4K to $10K, and even higher!)
GPS equipment can use the DGPS/WAAS correctional information to achieve
sub-meter/centimeter accuracy. Very high resolution usually requires
some post-processing of the collected data points on a PC. I think the
necessary software usually comes with the more expensive receivers.
Horizontal and vertical accuracy generally is better during the
nighttime hours when there is less tropospheric and ionospheric delay.
Garmin and Trimble were by far the most common GPS receivers mentioned
in the responses. People raved about the quality, reliability, and ease
of use for the Trimble products, but costs started at $4K and went up
from there. Great real-time DGPS/WAAS corrections and post-processing
software. Leica, Magellan, and DeLorme units were also positively
regarded but not as popular as Garmin or Trimble.
The Garmin units seem to have everything I need. Several are WAAS/DGPS
capable (< 3 m accuracy), can interact directly with ESRI products
(check the ESRI Technical Support site for scripts/utilities that
support Garmin receivers), and all cost less than $400. There are
numerous Garmin units available, all very similar, but the most popular
were the Garmin eTrex Vista, eTrex Legend, and GPSMAP models. Look at
http://www.garmin.com/ for details. Some things to consider are the
number of waypoints/routes it can store, the amount of internal memory
for downloading map data from CD, battery life, and DGPS/WAAS capability.
I decided to purchase a Garmin GPSMAP 76S receiver which I purchased
from the GPS Store at only $319.95. With a few accessories and one of
the MapSource CDs (necessary for downloading map data to the receiver),
I got everything for under $500. I also will try a GPS receiver
compact flash (CF) card that attaches to an HP iPAQ PDA device. On an
iPAQ, I can run ArcPad 6.0, load vector GIS data or aerial photography,
and do plenty of other GIS functions. The CF card is WAAS capable and
can be purchased from www.teletype.com for about $200. A booster
antenna ($59 - $129) and adapter ($12) is required to plugin the GPS
card to a laptop, which may be more useful to me than a PDA.
Some popular sites to get more info:
http://www.thegpsstore.com/
http://www.gpspassion.com/
http://www.gps4fun.com/
http://www.gpsdiscount.com
http://www.gps4educators.com/
Sorry for the long email! Thanks again for all of your help!
- John
*******************************************************************
Do not go where the path may lead, go instead where there
is no path and leave a trail.
- Ralph Waldo Emerson
*******************************************************************
John Callahan (302) 831-1978
IT - User Services
University of Delaware diodata@udel.edu
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