Location Accuracy Within Google Earth

I noticed that my Garmin never says my location accuracy is better than 10 feet. I suspect that's a hard stop--no matter how good it is, nothing better than 10 feet will be reported. I decided to check this by plotting the coordinates given from the Garmin device in Google Maps, then Google Earth, and discovered that if any inaccuracy exists, it's within these two programs. In each case, the program showed my location a good 40-50' from where I actually was. On the other hand, plotting those same coordinates within Bing Maps showed the location within 6' of where the Garmin actually was located. The beta version of MapQuest allows you to enter cooridinates, and it was better than Google, but not quite as good as Bing.

I realize that both the Garmin and the map program being used have inaccuracies that will be additive, but I am very surprised at the Google results. I'm curious if anyone here who has plotted their flight paths within Google Earth has seen similar inaccuracies. Your plane could be shown either flying underground or taking off and landing from a virtual airstrip in the sky.


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Comment by Overwatch on August 6, 2010 at 7:09am
Google Earth is using a spherical simplification of WGS 84 (an Earth geodetic model), whereas any decent mapping application, GPS included, is using the full deal - an oblate spheroid flattened at the poles. The error will be on the order of tens of meters and will vary with your latitude (should be zero close to the equator).

Also there's the factor of less-than-perfect quality of the map data Google sources from local authorities. And, especially if you're in a mountainous part of the country, there could be some error introduced by an inaccurate (3D) terrain model.
Comment by David on August 6, 2010 at 8:01am
I have used been using Google Earth extensively for a research project. I had the same question regarding the accuracy of the GE base image and did some ground truthing by using a Novatel Differential-GPS system to find the lat lon of some ground control points. I compared these to what GE said their lat lon were and found that in the X and Y at least the GE base imagery was accurate to within a half meter or so in my region. That being said, the terrain model is horrible and like was mentioned, the UAS tends to land underground :O
Comment by Paul Marsh on August 7, 2010 at 5:02am
Interesting info--thanks. I wasn' aware of some of these nuances of GPS and mapping.

Comment by Morli on August 7, 2010 at 5:40am
With miles & miles of flat plains all around me , I still find my self takeing off and landing under ground most of the times :(( , with no other better alternatives to GE in sight , I have to live with it I guess.


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