Not to be a cheerleader for Trimble, but they do offer another nice handheld unit that is much more accurate than the GeoXT. The unit is the GeoXH (http://www.trimble.com/geoxh.shtml). It offers real time sub-meter accuracy and 30-cm accuracy when post corrected. Also with the purchase of an additional Zephyr antenna, the accuracy can be increased to 20-cm (...but is an extra 10-cm really worth the price of an antenna at ~$2000?!). The unit costs ~$5000...and without the antenna, it doesn't require a backpack, which is really nice.
You might also consider the GeoBeacon, which sends realtime corrections to your GeoXT through a Bluetooth connection. I haven't used this product personally, but have heard that it is nice. Cheers, Mike On Thursday 30 March 2006 09:35, Dave Thomson wrote: > I would agree that the GeoXT is not a high caliber GPS unit. I was > dissuaded from using them by the very helpful techs at GeoPlane > Services: > > http://www.geoplane.com/trimble/pathfinderproxrs.html > > I have no experience with Leica products, but I wouldn't imagine a > handheld unit could rival the data quality of a backpack unit. I have > experience with the Trimble TSC1 Asset Surveyor/Pathfinder Pro XR > combination (dGPS) but was looking for the ability to utilize > orthorectified aerial photography in the field during data collection. > I thought that the GeoXT might fit the bill; I was told, unfortunately, > that the GeoXT's resolution was poor, and in particular the Z-axis was > very poor. > > Instead, he recommended renting one of their Pathfinder Pro XRS backpack > dGPS units, which they can pair with an Allegro CX field PC which takes > the place of the Trimble data collector. As you will see in the link > below the Allegro can hold up to a gigabite of data and display color > images very well. > > http://www.geoplane.com/junipersystems/allegrocx.html > > Of course not everyone can afford a Pathfinder Pro XR/S and an Allegro > CX. To be honest, I am not even sure how much they would run you > currently. I did see used Pathfinder Pro XR backpack units sell on eBay > in the $5-10,000 range! The big questions to ask yourself are: 1) do > you need this level of precision in your data, and 2) do you need to own > one of these setups? > > If the answers to the above are yes, and no, respectively, then consider > renting the units from a business such as GeoPlane. The last quote I > had from them for that setup was $1175 a month. The techs at GeoPlane > can help you decide what you require without the pressure of a sales > department. > > Hope that helps, > > David Thomson > > PS - I noted that one person discussed the ability to hold a lock on > satellites underneath a tree canopy with a GPS unit (handheld?). This > is not common. In fact I was surprised that someone had been 'offered' > data by their GPS unit in such a situation. Perhaps this is because (I > believe) most handheld units do not have good data quality assurance > functions and will offer any position they 'acquire'. User beware... > > High quality units will not even offer the user any data in such > situations. The Pathfinder Pro XR/TSC1 combination that I have used in > the past was only able to acquire a 3D lock in the near absence of > canopy; certainly the gap in the canopy had to be quite large (i.e. > expose sufficient sky to adequately 'see' enough satellites). In some > situations where I needed to acquire whatever data I could, I would > alter the settings to acquire the less accurate 2D data. Later, while > using the data, I was surprised at it's obvious innacuracies. > > The techs at GeoPlane did note that they have range poles can cabling > that they offer with their backpack units, which allow the user to raise > the antenna (what was it?) 10 feet (meters?) - sorry it's been awhile. > They said that this can help one acquire a signal in and around tree > canopies, but (of course) it is no guarantee. > > > -----Original Message----- > From: Ecological Society of America: grants, jobs, news > [mailto:[EMAIL PROTECTED] On Behalf Of Malcolm McCallum > Sent: Tuesday, March 28, 2006 7:22 AM > To: ECOLOG-L@LISTSERV.UMD.EDU > Subject: Re: GPS units and accuracy data > > I have not used a Leica GS20, how does it compare to the GeoXT? > also,=20 > =20 > Malcolm L. McCallum > Assistant Professor > Department of Biological Sciences > Texas A&M University Texarkana > 2600 Robison Rd. > Texarkana, TX 75501 > O: 1-903-233-3134 > H: 1-903-791-3843 > Homepage: https://www.eagle.tamut.edu/faculty/mmccallum/index.html > =20 > > ________________________________ > > From: Ecological Society of America: grants, jobs, news on behalf of = > Marlow G. Pellatt > Sent: Mon 3/27/2006 11:26 PM > To: ECOLOG-L@LISTSERV.UMD.EDU > Subject: Re: GPS units and accuracy data > > > > There are several GPS units with as good or better precision than the = > GeoXT. > You will need to decide what Basic mapping grade handheld units include > = > the > Leica GS20, Trimble Pathfinder series, and several other survey and = > mapping > level GPS units. The Trimble GeoXT is a good handheld unit with decent > accuracy but is not the most accurate or precise GPS on the market. > Geodetic and Survey grade GPS units are highly accurate but expensive. > = > I > have used several Garmins, Trimbles, CMT, and Leicas. I have been happy > with with Leica GS20 and Trimble GeoXT for collecting spatial data for = > most > ecological applications. > > Take a look at how the software will interface with your GIS and weather > = > you > need to look at maps and air photos etc of you site in the field. > > Here are some websites that may help you. > http://www.digitalgrove.net/GPS.htm > http://www.gmat.unsw.edu.au/snap/gps/gps_survey/chap4/chap4.htm > > > Cheers, > Marlow > > On Mon, 27 Mar 2006 14:41:46 -0600 [EMAIL PROTECTED] wrote: > > Forumites > > > > I wanted to find out more about GPS units, a topic many people have = > > asked > > > about on this listserv in the past. What I am trying to figure out is > > = > the > > > accuracy between an item like the Trimble Geo-Explorer XT compared to > > something more economically available like a Garmin 12 or Magellan > > product? =20 > > Are people happy using simple GPS units like the Garmin 12 to collect > > = > data > > > especially if you want to conduct geospatial analyses and if so how do > > = > you > > > deal with spatial accuracy and post processing data if it can be done. > > = > =20 > > > Also, what is the spatial accuracy compared to sub-meter GPS units. I > > would > > assume that it couldn't but it might also be difficult to do. I know > > = > the > > > Trimble GPS unit and Pathfinder Office makes this easier and you have > > better > > accuracy and precision, you even get a root mean square error with you > > data > > so that could be discussed. I appreciate any input and help from any > > one and > > look forward to hear what has to be said. You can reply to me and = > > then I > > > can summarize what was said to the listserv if need be. > > > > Thanks, > > > > Arvind > > > > > > Master's Student > > Department of Geography > > Virginia Tech > > http://www.geography.vt.edu/people/Grad%20Students/bhuta.htm > > Marlow G. Pellatt, Ph.D. > Coastal Ecologist > Parks Canada, Western Canada Service Centre > 300 - 300 West Georgia Street > Vancouver, British Columbia > V6B 6B4 Canada, and > School of Resource and Environmental Management > Simon Fraser University > Burnaby, British Columbia > V5A 1S6 Canada > Phone: (604) 666-2556 > Email: [EMAIL PROTECTED] -- Michael W. Sears, Ph.D. Associate Editor, Herpetologica Assistant Professor Center for Ecology Department of Zoology Southern Illinois University Carbondale, IL 62901 phone: 618-453-4137 web: http://equinox.unr.edu/homepage/msears http://www.ecology.siu.edu "Natural selection is a mechanism for generating an exceedingly high degree of improbability" Sir Ronald A. Fisher (1890-1962)
