shrug-l: Google earth accuracy estimate?

Porter, William B. william.porter at
Fri Mar 8 11:26:53 EST 2013

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     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] On Behalf Of Jim Robeson
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



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] On Behalf Of Sykes, John
Sent: Friday, March 08, 2013 9:28 AM
To: 'Amy Knight'; 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] On Behalf Of Amy Knight
Sent: Thursday, March 07, 2013 10:55 AM
To: 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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