two thousand twenty
Subscribe to Wayne County Life RSS post feed
Subscribe to Wayne County Life RSS comment feed
Subscribe to Wayne County Life by email
Wayne County Life on Facebook
SUBMITTED by Joe Dabes, Finger Lakes Trail Conference (18-Dec-2009)

Carrying my three field GPS units, I hiked the same 8.4 mile loop in the Citrus Tract of the Withlacoochee S. F. that I hiked last week, again on two consecutive 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: This time using the internal antenna mounted on top of the right shoulder strap of my day pack

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

Etrex Legend HCx: 301 feet (much worse than last week's 82')
Oregon 400t: 42 feet (similar to last week's 37')
60CSx without external antenna: 16 feet (similar to last week's 15' with external antenna)

Two conclusions:

1) Etrex Legend HCx can be quite inaccurate. Again, 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.

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.

Odometer measurements for the 8.4 miles were similar to last week's numbers:

Etrex: 8.37 and 8.36
Oregon: 8.31 and 8.26 miles
60CSx: 8.40 and 8.39 miles

Java Joe

P. S. If anyone is interested in examining the track data for these three units (60CSx with and without ext. antenna) 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 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.


You can make a comment, or trackback from your own site.

0 Comments to "Accuracy of GPS Units Part 2"

Post a Comment

Most Viewed - Last 30 days

Going Green

Church Life