shrug-l: Google earth accuracy estimate?

Lewers, Shawn slewers at
Fri Mar 8 12:38:44 EST 2013

I'm not sure but I don't think my iPhone actually uses GPS  satellite signals. I find that the geotagged photos and their locations are much more accurate when the phone is connected to a wireless network other than the  cell signal. Cell signal geotagging is location wise more general in my experience. Hence making me assume that GPS is not being used?  Anyone want to add to this?

sent from Shawn Lewers' IPhone

On Mar 8, 2013, at 11:27 AM, "Porter, William B." <william.porter at<mailto:william.porter at>> wrote:

I played with the internal GPS in my Nexus 7 after downloading free street software and GPS test software.   First I was tricked by the inertial system.  I was amazed:  It knows which way I’m facing.  I thought it had better than sub-meter.  I was wrong.

Are iPad and iPhone WAAS?

The software on the nexus in hard-coded to snap to the road lines.  It’s  pretty ridiculous in park or a large parking lot.
Nexus is not WAAS – I have heard this is an Android quirk.  Its precision [by free software] is on the order of 25 feet.  I’m sure it’s not better than that.   I compared it to my Fujitsu Win 7 tablet running Delorme Streetmap with a WAAS GPS, I saw no discernible difference until I pulled into the funeral home parking lot  [I played with the GPS to try and keep my mind off an otherwise bad day:  a lady younger than me died of cancer].

Anyway, the snap-to-the-line feature Jim spoke of is real and pretty tight.  Road data is so good on Garmin, Tom Tom [even Magellan] that details of an urban clover leaf show up and snap-to-the-line gives an inflated image of precision.  It’s wild when details are missing and the green arrow is running across grass [or rarely cheats to a road you know is wrong].

Google maps on nexus are less strict about snapping to the line.

William  B. Porter     william.porter at<mailto:william.porter at>     850 412 5972
Application Coordinator for GIS / Infrastructure
Florida A&M University
Perry-Paige, West Wing Ground floor,
Office 1 -C
1740  S. M L King  BLVD
TLH FL 32307

From: shrug-l-bounces at<mailto:shrug-l-bounces at> [mailto:shrug-l-bounces at] On Behalf Of Jim Robeson
Sent: Friday, March 08, 2013 9:36 AM
To: 'Sykes, John'; 'Amy Knight'; shrug-l at<mailto: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


NOW with the only Trimble Survey and Mapping Repair Center in Florida!

Tallahassee Office
Phone (850) 656-6075
Cell (850) 212-0030
Fax (850) 656-1350
mailto:Jim at<>

Corporate Office
621 Brookhaven Drive
Orlando, FL  32803-2503
Phone: (407)601-5816
Fax: (407)601-5826
Toll Free: (888)782-1997

 Products:  Trimble Mapping, Trimble Survey, ESRI, Leica HDS Laser Scanners, LTI, Ricoh, Laser Craft, SECO

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

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<>.
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

SHRUG-L mailing list
SHRUG-L at<mailto:SHRUG-L at>
-------------- next part --------------
An HTML attachment was scrubbed...
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image001.jpg
Type: image/jpeg
Size: 5153 bytes
Desc: image001.jpg
Url :

More information about the SHRUG-L mailing list