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

Poly, William WPoly at calacademy.org
Wed May 8 07:38:16 CDT 2013

GPS accuracy has varied temporally due to restrictions by the US govt. for military/security reasons (Selective Availablity).  See:



From: taxacom-bounces at mailman.nhm.ku.edu [taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Robert Mesibov [mesibov at southcom.com.au]
Sent: Wednesday, May 08, 2013 12:48 AM
Subject: Re: [Taxacom] Accuracy of GPS Receivers, was...

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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