Comments on: Why Are My GPS Positions In The Wrong Place In Google Earth? http://freegeographytools.com/2007/why-are-my-gps-positions-in-the-wrong-place-in-google-earth Exploring the world of free tools for GIS, GPS, Google Earth, neogeography, and more. Fri, 20 Apr 2012 04:10:35 +0000 hourly 1 http://wordpress.org/?v=3.3.2 By: Brian Kenward Sr. http://freegeographytools.com/2007/why-are-my-gps-positions-in-the-wrong-place-in-google-earth/comment-page-1#comment-3006 Brian Kenward Sr. Sun, 29 Nov 2009 04:03:21 +0000 http://freegeographytools.com/?p=36#comment-3006 The realestate usefullness of the garmin and google earth combination is hindered because the huge difference in accuracy. Who is an expert in this ? The realestate usefullness of the garmin and google earth combination is hindered because the huge difference in accuracy.

Who is an expert in this ?

]]> By: Leszek Pawlowicz http://freegeographytools.com/2007/why-are-my-gps-positions-in-the-wrong-place-in-google-earth/comment-page-1#comment-39 Leszek Pawlowicz Tue, 16 Jan 2007 16:38:09 +0000 http://freegeographytools.com/?p=36#comment-39 Good point about the terrain. I believe that Google Earth uses 30-meter terrain data for the US, but 90-meter for most of the rest of the world. So in areas of extreme topography, images won't be "stretched" properly to fit the terrain. The Matterhorn in Switzerland was the classic example of this in Google Earth, but GE improved the accuracy of the elevation data there so that it renders more accurately now.<br /><br />Google Earth says that it uses the standard elliptical WGS84 model:<br /><br />http://earth.google.com/userguide/v4/ug_importdata.html<br /><br />But even the elliptical model is too simplistic, and trying to wrap data in the geographic (Plate Carree) on such a simple model of the Earths' shape will introduce additional errors. Good point about the terrain. I believe that Google Earth uses 30-meter terrain data for the US, but 90-meter for most of the rest of the world. So in areas of extreme topography, images won’t be “stretched” properly to fit the terrain. The Matterhorn in Switzerland was the classic example of this in Google Earth, but GE improved the accuracy of the elevation data there so that it renders more accurately now.

Google Earth says that it uses the standard elliptical WGS84 model:

http://earth.google.com/userguide/v4/ug_importdata.html

But even the elliptical model is too simplistic, and trying to wrap data in the geographic (Plate Carree) on such a simple model of the Earths’ shape will introduce additional errors.

]]> By: GearthBlog.com http://freegeographytools.com/2007/why-are-my-gps-positions-in-the-wrong-place-in-google-earth/comment-page-1#comment-38 GearthBlog.com Tue, 16 Jan 2007 13:09:22 +0000 http://freegeographytools.com/?p=36#comment-38 A couple of other points:<br /><br />* 3D Terrain - GE has terrain and the image is stretched over the terrain. The terrain is not detailed enough to be an exact match so the photo will be stretched differently.<br /><br />* The image errors can be attributed to the fact Google uses a spherical WGS84 base model, not elliptical. But, more often it is due to the provider Google got the data from not accurately processing their imagery data. Google is trying to enforce better QA. A couple of other points:

* 3D Terrain – GE has terrain and the image is stretched over the terrain. The terrain is not detailed enough to be an exact match so the photo will be stretched differently.

* The image errors can be attributed to the fact Google uses a spherical WGS84 base model, not elliptical. But, more often it is due to the provider Google got the data from not accurately processing their imagery data. Google is trying to enforce better QA.

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