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Captain Paul - GPS Info in Louisiana
Capt Paul

How accurate are GPS coordinates taken from Google Earth? If I use Google Earth on my computer to find a spot in Lake Pont. how close will the GPS coordinates put me to that spot? Someone told me that the government required a deviation that altered the accuracy.
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Response by Captain Paul
February 03, 2015 at 5:55pm
Google Accuracy
~ Captain Paul's response ~

Yes, No and Maybe.

I guess that covers it all. But seriously, they all could apply depending how you are using the settings in your GPS unit as compared to the Options in the Google Earth program.

Let me explain. My information is that Google Earth uses a EGM96 Geoid in displaying their Google Earth programs.

EGM96 (Earth Gravitational Model 1996) is a geopotential model of the Earth consists of coefficients complete to degree and order 360. Basically it is a model of the earth as devised in 1996 which allows the user to precisely place positions on the surface of the ellipsoid. This model is the result of a collaboration between the National Imagery and Mapping Agency (NIMA), the NASA Goddard Space Flight Center (GSFC), and Ohio State University.

Very accurate positions can be placed on the Geoid with regards to vertical and horizontal locations. Some map makers use an ellipsoid model for their model. The Geoid model is usually more accurate for positions that are in elevations that are above the surface of the Geoid, whereas the Ellipsoid model is usually better used for relative flat areas near to sea level.

Either way, I believe that the Google Earth images are corrected to use WGS 84 datum. So if that is the datum that you use, simply enter the Google coordinates into your unit. Be sure to check the position format to be sure that they also agree. You can either change the Position Format ( Location) in your GPS unit or you can change the Google Earth display by going to the TOOLS/Options link at the top of the program and select what ever position format you normally use. Be sure that they agree.

So, if you are using your GPS unit in a relative flat area, such as Louisiana, or any sea level environment, I would assume that the figures are fairly accurate. However, if you are using the WAAS feature in your GPS unit in order to get the 3 meter accuracy via the differential system, your position via Google may only be to a position accuracy of 20 meters.

I would use the Google info but use it with suspect. When you get to the actual location you should use your WAAS activated GPS unit of “refine” the position.

If you need any additional information, get back with me.

Captain Paul
February 03, 2015 at 6:43am
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