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Friday, December 11, 2009

Java Joe Compares GPS Units

comparing GPS track errors
Etrex Legend HCx tracks (on MapSource) at their maximum distance from each other (the yellow line is the measured 82 feet)

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a guest post by "Java" Joe Dabes

Joe Dabes is the Finger Lakes Trail Mapper and has GPSed over 1700 miles in the last 6 years. He spends winters in Florida, and this test was done there. Here is his comparison of three units. JHY

Carrying my three field GPS units, I hiked the same 8.4 mile loop in the Withlacoochee State Forest here in central Florida on two consecutive days. Overhead canopy was light to moderate, primarily live oaks and long leaf pines. The three units all have the Garmin high sensitivity internal antennas that have been available for about three years now. All three were set to gather track points every 4 yards.

1. The Etrex Legend HCx (~$200) mounted on top of the left shoulder strap of my day pack
2. Oregon 400t (~$400, touch screen unit) carried in my left hand about a foot in front of my waist
3. GPSmap 60CSx (~$300) with external amplified Gilsson antenna (~$20) mounted on my hat (Note: when the external antenna is plugged in, the internal antenna is "off")

Note that the Extrex Legend and Oregon do not accept external antennas.

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

Etrex Legend HCx: 82 feet
Oregon 400t: 37 feet
60CSx with ext. antenna: 15 feet - clearly the best setup

Above is a clip of the Etrex Legend HCx tracks (on MapSource) at their maximum distance from each other (the yellow line is the measured 82 feet): Furthermore the Etrex Legend has been much more inaccurate on four occasions when I carried it in my hand at waist level in repeated loops or out-and-backs: three times the tracks differed by ~500 feet and once ~1000 feet. I have never noticed such great inaccuracies with the 60CSx or Oregon.

Odometer measurements (which are based on readings taken every 1 second) for the 8.4 miles:

Etrex: 8.32 and 8.37 miles
Oregon: 8.29 and 8.33 miles
60CSx: 8.44 and 8.43 miles (I suspect this is the most accurate)

I hope to do this same loop twice more with 60CSx without external amplified antenna attached.

-Java Joe

See Garmin Colorado Review

5 comments:

Tom Salwasser said...

Hey Joe, thanks for the interesting article. All 3 of the units you compare fall within the margin of error for accuracy that I need. I recently upgraded from an eTrex Vista to an eTrex Vista H. The H models contain the high sensitivity internal antenna that you mention and make a world of difference. Even under heavy cover, in my pocket, or in my pack I kept a good signal and track log. This was not the case with my older unit. I avoid color units, they tend to go through batteries faster.

bill said...

Did you record how many satellites you were reading on each one? Just curious.

Bill:wildramblings.com

kabjnd said...

Tom,

As I said, my Etrex Legend HCx has been very erratic compared to the old trusty 60CSx. Etrex Legend being off as much as 1000' is totally unacceptable for the FLT/NCT mapping work I do. I don't believe color units consume more battery power, and they are far easier to view.

Bill, Lots of satellites, at least a dozen all of the time.

Again, for accuracy, gotta have an external amplified antenna!

Java Joe

Tom Salwasser said...

I agree JJ, if you're making maps the Etrex Legend H may not be the unit you want. For getting in and out of the woods, strong satellite lock in heavy cover, 3 day battery life on 2 AAs, light weight and huge map capacity, you can't beat the bang for the buck. Sometimes a thousand feet is close enough and sometimes it ain't! Really enjoyed your article.

Tom Salwasser said...

oops! I have the etrex vista H, not legend.