shrug-l: Google earth accuracy estimate?
slewers at fsu.edu
Fri Mar 8 12:22:27 EST 2013
I will back Jim up on his comments. I can show you path data we collected recently on campus even after being post processed on a submeter receiver that shows a great many multipath errors in certain situations. I have long suspected that vehicle based navigation did a bit of modeling, error smoothing and the Like since GPS is not always hyper accurate at all times.
sent from Shawn Lewers' IPhone
On Mar 8, 2013, at 9:36 AM, "Jim Robeson" <jim at gpserv.com<mailto:jim at gpserv.com>> wrote:
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.
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From: shrug-l-bounces at lists.dep.state.fl.us<mailto:shrug-l-bounces at lists.dep.state.fl.us> [mailto:shrug-l-bounces at lists.dep.state.fl.us] On Behalf Of Sykes, John
Sent: Friday, March 08, 2013 9:28 AM
To: 'Amy Knight'; shrug-l at lists.dep.state.fl.us<mailto:shrug-l at lists.dep.state.fl.us>
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.
Please take a few minutes to share your comments on the service you received from the department by clicking on this link DEP Customer Survey<http://survey.dep.state.fl.us/?refemail=John.Sykes@dep.state.fl.us>.
From: shrug-l-bounces at lists.dep.state.fl.us<mailto:shrug-l-bounces at lists.dep.state.fl.us> [mailto:shrug-l-bounces at lists.dep.state.fl.us] On Behalf Of Amy Knight
Sent: Thursday, March 07, 2013 10:55 AM
To: shrug-l at lists.dep.state.fl.us<mailto:shrug-l at lists.dep.state.fl.us>
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-
GIS Program Specialist
Florida Natural Areas Inventory
Florida State University
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Ph. 850-224-8207 x214
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