[Taxacom] Accuracy of GPS Receivers, was...

Robert Mesibov mesibov at southcom.com.au
Tue May 7 23:48:23 CDT 2013

Over a month last (austral) summer I took 2 readings a day (total 50 observations) with my old faithful Garmin eTrex (vintage 2005) from exactly the same spot in my backyard, always allowing the readings to settle down over the course of a minute or two.

I recorded the date, time, location (UTM), elevation and declared accuracy. You can download the raw data here: http://www.polydesmida.info/GPS_repeats_Mesibov_2012.csv and use them as you like.

As expected, elevation was the most variable data item. I've heard it rule-of-thumbed that GPS elevation precision is ca 1.5x horizontal precision under the best of conditions.

What's more important to understand is that GPS elevation is height above an Earth model, not above sea level, and can be tens of metres different from a.s.l. Comparing heights on 10m contour maps with heights from Google Earth, I find Google Earth elevations are rarely more than 10m off.
Dr Robert Mesibov
Honorary Research Associate
Queen Victoria Museum and Art Gallery, and
School of Agricultural Science, University of Tasmania
Home contact: PO Box 101, Penguin, Tasmania, Australia 7316
Ph: (03) 64371195; 61 3 64371195

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