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Obtaining Elevation Profiles with Google Earth
Have you put Google Earth (G-E) on your computer yet? I have been using it for a while now, and I've probably just scratched the surface in terms of its capabilities. There is one particular feature I want to share with you.
It used to be that you had to buy access to a 3-second database to run elevation profiles. However, with G-E, all you need is to find your start and end points. Now admittedly, I still use Google Maps to find coordinates of places occasionally. That's pretty straightforward -- just open a browser, go to Google maps, expand the map (zoom in) and find the exact spot you are looking for. Then, right-click on the spot, highlight "what's here," and left-click on that. You'll notice the coordinates are given to you in the search window box immediately above the map display. (You can copy and paste those in the search window for G-E.)
Google Earth is even easier than that though. After downloading it, and installing it on your computer, you'll open the program, and then zoom in on the spot you are interested in.
Once you open G-E in the upper left hand corner you'll see the yellow pushpin icon that G-E labels as add placemark. Left click on that; drag the pushpin symbol to exactly where you want it; then give it a name, and click OK.
Keep in mind that the coordinates you are given are of WGS84 reference.
To find an elevation profile, you need a second point, of course. For this demonstration I picked an AM transmitter site that is across the San Francisco bay from Sutro Tower.
Along the upper toolbar for G-E you'll see an icon called show ruler and this is the tool we're going to use to derive the elevation profile. Left click on that icon; then zoom way in on your starting point. (The closer you zoom in, the more accurate this elevation profile will be.) When you have your starting point, left click on it. Now zoom out (you'll notice a yellow line tagged on your starting point) and find your point B; zoom way in (for accuracy) and then when you're sure that you're right on point B, left click again. This terminates the yellow (ruler) line.
After you click save you'll be prompted to give this new path a name, which you must do to get the elevation profile. Once done, the path will be saved in the left column (places). In the upper left corner, find edit, then show elevation profile and click on that.
This is the result. You'll also find that you can move the red arrow around with your mouse, and the vertical line (shown right in the middle of the elevation profile) moves as well, showing you the elevation at that particular spot.
If you have another use for G-E (pertaining to broadcast engineering) I'd like to hear about it.
Irwin is RF engineer/project manager for Clear Channel Los Angeles. Contact him at firstname.lastname@example.org.
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