Google Earth Question?

[Rege-PA]

When I and a friend try to lock on and co-ordinate the same feature on google earth our co-ordinates do not match. The variation is off about 3 minutes. Our computer settings for google earth are exactly the same but I`m not sure if we are running the same version. Any ideas?

[Clay Diggins]

From Google:

Quote

Google makes no claims as to the accuracy of the coordinates in Google Earth. These are provided for entertainment only and should not be used for any navigational or other purpose requiring any accuracy whatsoever.

Our imagery varies from sub-meter resolution in major cities to 15 meter resolution for most of the earth's surface, with a global base resolution of 1KM. Since our database is constantly being updated, we cannot state a specific resolution for any geographic region.

Google uses a non standard projection. It doesn't matter which positional tool notation you choose from the options the projection is the same for every Google Earth map. Accuracy is a function of the base data and the projection method. Changing from lat/long to UTM display doesn't change the accuracy of the mapping.
 

[fredmason]

dang I didn't know they had UTM...I better do some homework!

thanks

fred

[Clay Diggins]

Google Earth uses Lat/Long in decimal degrees as their base reference. It's a requirement of the KML/KMZ file format created and used by Google.

You can convert any Lat/Long or UTM coordinates with a little math. That's what Google is doing when they offer coordinates in any form but the native Decimal Degrees of Lat/Long.

The coordinate conversion math is actually accomplished locally by your computer, Google just provides the equation your computer uses to show coordinates other than Decimal Degrees.

If UTM is more useful for you please use that metric system. You should be aware that when you near the westernmost portions of a UTM zone the ground accuracy decreases. Also accurate ground measurements are not possible with Mercator projections. Distance calculations are only relative when accomplished on the same true east/west line.

Making accurate mapping systems is not an easy task. Often visual appearance must be sacrificed to maintain accuracy. Google took the path of convenience, easy maintenance and better appearance at the expense of accuracy with their mapping system. They have been public about those limitations as you can see from their quote in my previous post. As long as you are aware the accuracy issues that you are seeing are built into the system Google Earth can be useful but you can't rely on the positional accuracy of what you learn.

If you are using the Google Earth Terrain "3D" feature turn it off and your accuracy will be much better. Google Earth does not align the 3D terrain to their coordinate reference so it's essentially impossible to get  good coordinate data with the 3D feature on.

[Rege-PA]

3 hours ago, Clay Diggins said:

If you are using the Google Earth Terrain "3D" feature turn it off and your accuracy will be much better. Google Earth does not align the 3D terrain to their coordinate reference so it's essentially impossible to get  good coordinate data with the 3D feature on.

Thanks Clay for the info, will give it a try.