Wednesday, 3 March 2010

Converting Google Earth Lat and Long to coordinates that you can enter into your GPS

Following on from my blog about converting Google Maps URL into Lat and Long to enter into your GPS, here’s some info on how to convert from Google Earth to GPS coordinates.
Open Google Earth program and navigate to the location that you are interested in (search or fly there).
Click ‘Add placemark’
Drag the placemark to the spot that you want the GPS coordinates for (you will notice that the “New Placemark” window will open)
Click “OK”
Right click on the newly created placemark
Select the “Save place as…”
Enter a filename to save the placemark to your computer (eg: filename.kmz)
Browse to the file on your computer (using Internet Explorer)
Rename the file to have a .zip extension (eg:
Double click the .zip file and it should open the zip file’s contents to show a file called doc.kml
Right click on doc.kml file and select “View”
The file should open and then search for <coordinates>"
The GPS coordinates should then be displayed that you can enter into your GPS
eg: <coordinates>31.07549643928536,-17.79160330480021,0</coordinates>
Lat: 17°47'29.77"S, Long: 31° 4'31.79"E

See here for a GPS Latitude and Longitude Converter

If you are not familiar with latitude and longitude, here is a crash course in navigation
Lines of latitude and longitude are hypothetical lines on the surface of the Earth.
On the Earth, lines of latitude are circles of different size.
The longest (largest in diameter) is the equator, whose latitude is zero, while at the poles, at latitudes 90° north and 90° south (or -90°), the circles shrink to a point.
On the Earth, lines of constant longitude (meridians) extend from pole to pole, and cross the lines of latitude.
Every point on the surface of the Earth has coordinates where a given line of latitude and a give line of longitude intersect (cross).
To sum it up, latitude is measured from the equator, with positive values going north (0 to 90) and negative values going south (0 to -90).
Longitude is measured from the Prime Meridian (which is the longitude that runs through Greenwich, England), with positive values going east (0 to 180) and negative values going west (0 to -180).
So, for example, 65 degrees west longitude, 45 degrees north latitude is -65 degrees longitude, +45 degrees latitude. Now that the designations (and reasons for them) are perfectly clear, here is the set of formulae if you need to do this manually.

Degrees Minutes Seconds to Degrees Minutes.m (GPS)
Degrees = Degrees, Minutes.m = Minutes + (Seconds / 60)

Degrees Minutes.m to Decimal Degrees
.d = M.m / 60, Decimal Degrees = Degrees + .d

There are 60 minutes in a degree and 60 seconds in a minute; 3600 seconds in a degree. There are 360 degrees in a complete circle or sphere but in all longitude and latitude measurements, the total of the degrees is expressed as 2 halves of 180 degrees each.

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