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Politics : Politics for Pros- moderated

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To: goldworldnet who wrote (373277)	7/16/2010 9:40:59 PM
From: ManyMoose	Read Replies (2) of 793877

Thanks, Josh. That diagram really doesn't show how GPS works very well, though. A diagram that did a good job would have to be in four segments or panels. The first panel would show one satellite emitting a signal toward the earth. That signal would scribe a circle around the earth's surface representing every place the signal reaches the surface at exactly the same time, much like the black band at the top of a white sock reaches one, two, three etc. inches up your ankle at the same time all the way around your leg. The position of that circle is determined by how long it takes for the signal to get from the satellite to the earth, and then for the circle to slide around the earth like the black band on a sock. That's a little wordy, but understanding it is essential to understanding all the other diagrams. The second diagram would should two satellites emitting signals. The circles they scribe would intersect in two places on opposite sides. So you know that your position has to be in one or the other of the two intersections. The third segment rules out one of the two intersections by a signal from a third satellite. Only one of the two intersections can receive the third signal at the measured time received by your GPS device. The 3rd time interval that you actually got would agree at one point but not at the other, so it couldn't possibly be the other point. The system knows how to calculate the latitude and longitude of every point on earth by very precise calculations of the exact time it takes all three signals to arrive at your location. A fourth signal allows the system to calculate elevation. Sometimes you can get more satellites, which helps to improve the precision of your fix. When I became familiar with GPS it was difficult to get signals through a dense tree canopy and in the mountains. I can't imagine how it would be possible for GPS to guide a drill bit under a mile of water and even more bedrock.

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