Before you get started, let me give you a brief tutorial on GPS. GPS, which stands for Global Positioning System, is a system of satellites that transmit signals. GPS devices use these signals to calculate the position of an object. There are a total of 24 satellites transmitting signals all around the Earth at any given moment, but your device can only see the signal from a much smaller set of satellites.

Each of these satellites transmits a very accurate time signal that your device can receive and interpret. It receives the time signal from each of these satellites, and then based on the delay—the time it takes the signal to reach the device—it calculates the receiver's position, which is in turn based on a procedure called triangulation. The next two diagrams illustrate how a device uses the difference between the delay data from three satellites to calculate its position. The following is the first diagram, depicting the device at its initial...