shrug-l: Google earth accuracy estimate?

Sykes, John John.Sykes at
Fri Mar 8 09:47:24 EST 2013

Agreed, that is why I took 10 to 20 readings over a several day period and averaged them.

The Garmin is an aviation hand-held version, but an old one.  I got it when they first became available for aircraft.  I had it with me on a trip from Philly to Florida (via Atlanta) in the early 1990' (pre-9-11 days).  It was on a MD88 equipped with R-NAV and maybe INS (but probably not).  The Flight Attendant apparently told the captain that the passenger in row whatever had a strange type of radio with him.  The captain came back to my row and sat down next to me.  I asked him if he knew exactly where we were and how fast we were moving (because of summer thunderstorms we were a lot further west than planned).  He looked at the display on the Garmin and said, "Probably not as accurately as you do."  A few minutes later, he sent the First Officer back to "get a load of this".

-- John

From: Jim Robeson [mailto:jim at]
Sent: Friday, March 08, 2013 9:36 AM
To: Sykes, John; 'Amy Knight'; shrug-l at
Subject: RE: shrug-l: Google earth accuracy estimate?

Gamins and Tom Tom for vehicles have a good bit of modeling in their display when using on a street map product; snap to the line.  But they are typically 3ish meters in a good place and 5-10, maybe even more, in a really bad place.  Bad being in around buildings or a heavy multipath environment.

Jim Robeson

James M. Robeson
Mapping/GIS Sales, Trimble Certified Trainer

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From: shrug-l-bounces at<mailto:shrug-l-bounces at> [mailto:shrug-l-bounces at] On Behalf Of Sykes, John
Sent: Friday, March 08, 2013 9:28 AM
To: 'Amy Knight'; shrug-l at<mailto:shrug-l at>
Subject: RE: shrug-l: Google earth accuracy estimate?

There are errors when using Google Earth or Google Maps to plot lat/longs in Florida.  But in my experience they are relatively minor, because Florida is FLAT!  In my experience elevation differences cause many if not most of the errors.  The major problems I see involve plotting addresses, where things may be off by half a block.  If you find the particular building and plot it, it usually is accurate to about 10 meters or better.  Part of the error comes from the aerials used and how well they were georeferenced.  Since most aerials for the State are now being flown with a digital linear scanner, they are much less prone to these errors.

I just checked my own home, where I have a very visible location on my back deck that I have used to check several GPS's for accuracy.  Pulling the Google Earth lat/long quickly (they have a brand-new aerial, shot only a few months ago) and comparing it to the GPS average was within 1 meter.  T'ain't too shabby!  Probably 1 ft of that error is my shaky hand on the trackball.  Oh, by the way, they weren't survey-grade GPS's either; 1 Garmin, 1 DeLorme and my roommate's TomTom.  But I took several readings on different days and averaged them out.

-- John

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From: shrug-l-bounces at<mailto:shrug-l-bounces at> [mailto:shrug-l-bounces at] On Behalf Of Amy Knight
Sent: Thursday, March 07, 2013 10:55 AM
To: shrug-l at<mailto:shrug-l at>
Subject: shrug-l: Google earth accuracy estimate?

Hi-  A year or so there was SHRUG exchange of 'bad' google earth examples.   Does anyone know of an accuracy estimate for Florida?  We receive point location data from many different sources but more and more data are coming in with Google Earth as the source of the location (lat/long).   We need to be able to say what locational uncertainty those data have.   How 'off' could a point be, plotted on Google Earth vs. Florida aerial ortho imagery?  Thanks for any information-

Amy Knight
GIS Program Specialist
Florida Natural Areas Inventory
Florida State University
1018 Thomasville Rd, Suite 200-C
Tallahassee, FL 32303
Ph. 850-224-8207 x214<>
Science for Conservation

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