shrug-l: Google earth accuracy estimate?

Kevin Shortelle kevinshortelle at bellsouth.net
Fri Mar 8 10:12:24 EST 2013


John:

I appreciated your astute "back of the envelope" approach of quantifying Google Earth accuracy -- that is, establishing ground-truth with averaged GPS measurements and then comparing with Google Earth data.

Regards,
Kevin
************************************************
Manager, Integrated Systems Group
System Dynamics International, Inc.
9116 SW 51st Road, Suite 102
Gainesville, FL 32608
Phone/Fax: (352) 371-8035
www.sdi-inc.com
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  ----- Original Message ----- 
  From: Sykes, John 
  To: 'Amy Knight' ; shrug-l at lists.dep.state.fl.us 
  Sent: Friday, March 08, 2013 9:27 AM
  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 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
  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  

   

  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

   

  www.fnai.org

  Science for Conservation

   



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