[ft-l] Fw: Accuracy of Garmin "Field" GPS Units

geyerpd at comcast.net geyerpd at comcast.net
Mon Dec 21 11:47:15 CST 2009


Hi Joan....I do not know about Joe having fun but I just hiked along the Suwannee river segment and had great fun. We now have a brand new, reroute removing a long road walk and replacing it with more walk along the river, including a section of rapids. The downside is that it no longer takes hikers past the Madison shelter. 

Looks like a lot of folks will be on the FT thru-hiking this year. 

Paul Geyer 

----- Original Message ----- 
From: bluetrail at aol.com 
To: ft-l at backcountry.net 
Sent: Monday, December 21, 2009 10:50:19 AM GMT -05:00 US/Canada Eastern 
Subject: Re: [ft-l] Fw: Accuracy of Garmin "Field" GPS Units 


Yeah, but was the hike fun? Did you get any good animal sightings? Did you enjoy the scenery? 

Joan, the non-technical 



-----Original Message----- 
From: Joe Dabes <kabjnd at msn.com> 
To: FT Listserv <ft-l at mailman.backcountry.net> 
Sent: Fri, Dec 18, 2009 7:52 pm 
Subject: [ft-l] Fw: Accuracy of Garmin "Field" GPS Units 




Greetings, 


Carrying my three field GPS units, I hiked the same 8.4 mile "A" loop in the Citrus Tract of the Withlacoochee S. F. on separate days (overhead canopy light to moderate). The three units all have the Garmin high sensitivity internal antennas that have been available for ~3 years now. All three were set to gather track points every 4 yards. 

Etrex Legend HCx: Mounted on top of the left shoulder strap of my day pack 
Oregon 400t: Carried in my left hand about a foot in front of my waist 
GPSmap 60CSx using internal antenna: Mounted on top of the right shoulder strap of my day pack 
GPSmap 60CSx using external amplified Gilsson antenna: Antenna mounted on top of my hat 

Here are the results for the maximum distance between the two tracks for each unit over the 8.4 mile repeats: 

Etrex Legend HCx: 301 feet 
Oregon 400t: 42 feet 
60CSx without external antenna: 16 feet 
60CSx with external amplified antenna: 15 feet 

Three conclusions: 

1) GPSmap 60CSx is clearly the most accurate. 

1) Etrex Legend HCx can be very inaccurate. I have seen the maximum several times at ~500' and once ~1000'. Perhaps the problem is with my particular unit? I don't think so, as two others have sent me track data using this same model unit and the tracks differed at times several hundred feet from the same trail that I GPSed with my 60CSx with ext. antenna. This unit is popular as it sells for ~$100 less than the most popular 60CSx. 

2) For the 60CSx under light to moderate canopy it seems to make little difference whether the external antenna is used (as long as the unit is mounted high, such as the top of a shoulder strap). However, under the heavy canopy we have summers along the FLT, I know that using the external antenna does increase accuracy, sometimes considerably. 

-Java Joe, Finger Lakes Trail Conference GIS Guy, now in our winter home near Ocala FL 

P. S. If anyone is interested in examining the track data for these four tests over this 8.4 mile loop, I would be happy to send it as .gpx files. 
P. P. S. I determined the maximum distance between the two tracks by zooming Garmin MapSource in to the maximum (80' scale) and scrolling over the tracks for the entire 8.4 miles, and using the "measure" tool measure distance between the two tracks. 


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