Saturday, July 28, 2018

How to Extract Accurate Point Coordinates and Heights from Google Earth

In this post, we will use free software to extract height/elevation/altitude of points above sea level for any location in the world from DEM (digital elevation model) databases. This is fairly good data for drawing contour maps, draw a profile of a track or to colorize points by height above sea level.

The sources of the elevation data is from a DEM (digital elevation model) databases as explained below:-

DEM data sources
USGS: NED The U.S. Geological Survey's excellent National Elevation Dataset covers the United States, Canada, and Mexico. 1 arc-second (~30-meter) horizontal resolution is available in most areas (NED1). For Alaska, 60-meter data is also available (NED2). 
NASA: SRTM1 NASA's SRTM1 database (from the Space Shuttle Radar Topography Mission) has a resolution of about 30 meters. Previously, SRTM1 data was only available for the United States (and was not very useful because NED1 is generally better), but recently NASA has released SRTM1 tiles for the entire world. GPS Visualizer's server does not contain the full global dataset, but it does contain all of Europe, Japan, South Korea, and Taiwan, as well as parts of Australia, New Zealand, and South Africa. Additional locations will be installed upon request. 
ASTER: The ASTER GDEM is a joint product of NASA and the Japanese Ministry of Economy, Trade, and Industry (METI). ASTER has very good 30-meter coverage of the entire world, but the awkward download process and the massive size of the database make it impractical to store all of it on ASTER files for Iceland are available, however, since none of the other 30-meter databases cover that area. (As with SRTM1 data, additional files can be added upon request.) 
NASA: SRTM3 NASA's SRTM3 dataset includes 90-meter resolution for the entire world.

For precise engineering and surveying works, other methods that involves direct measurement on the field using level instrument is recommended. With that said, lets see how to extract the elevation data.

Required Software/Tools are:-
Get a copy of the following software if you don't have them, they are free to download.
a~ Google Earth
b~ GPS Visualizer
c~ TCX Converter

Step to follow:-

Step 1:
Open Google earth and zoom to the location where you want to extract elevations for.

Step 2:
Then pick the "Add Path" tool to draw paths across the site where you want the coordinates and elevations for. The more dense the points, the better result you will get for generating contour lines for the site.

Save the drawn paths with any name, I used 'site_Path' as my path name as seen below.

Step 3:
Right click on the path layer and save the place as .kml file

Step 4:
Open GPS Visualizer website and convert the 'site_Path.kml' file you saved to a GPX file as seen below

Step 5:
Open TCX Converter software you installed earlier and upload the GPX file. You should see the elevations along side the coordinates of the points.

Note: If your GPX file doesn't contain the elevations of the points, copy the XML code as provide on the download page in step 4 and save it as a .gpx file using a text editor.

Step 6:
Export the file and save it as CSV or any other file you want for further processing.

That is it!
Thank you for following....

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