The Evolution Of GPS

Everybody uses GPS as a matter of course to find their way to new locations. It is an integral aspect of our daily lives with multiple applications. It is an essential tool for the well-informed fleet manager. Despite our familiarity with GPS, few know its history or how it works. We rectify that shortfall with the following description of how GPS came about, and the concepts needed to make it operate with such accuracy.

⚡ The History of GPS

The Evolution Of GPS | The History of GPS

The USA DOD (Department of Defense) designed GPS in the early seventies. The form we use today was released to the public in 2000. It exists in two forms: PPS for the DOD and its allies, and SPS, which was less accurate, was available to the rest of us. This was to protect national security, but as defense capabilities increased, the accuracy of the SPS increased. PPS stands for Precise Positioning Service (as opposed to standard -SPS). Today, SPS is very precise but not as exact as PPS.

The following concepts are essential to understanding how GPS determines the requested position. We unpack these below.

⚡ Trilateration

The Evolution Of GPS | Trilateration

Trilateration is one of the concepts that allows fleet vehicle GPS tracking. GPS uses the position of four satellites that can be seen from any single place in the world. It makes use of 24 operational satellites and an additional five backing these up to ensure that four are always visible. Each satellite moves twice around the globe on a daily basis.

While the intersection of three of these points will mark your position on the ground, this is not enough. Because the earth is neither a perfect sphere nor completely flat, one more point is needed to determine the elevation above sea level of the position being sought. Thus, four points are needed to get an exact fix.

⚡ How Distance Is Measured?

The Evolution Of GPS | How Distance Is Measured?

The satellite uses an electronic digital signal of its own time and position. The GPS subtracts this from its own time to provide the distance between the GPS and the desired location. An atomic clock is used to compute this due to its supreme accuracy. Atomic clocks in the satellites use the vibration of atoms for this, while GPS is fitted with regular quartz clocks due to the cost of atomic clocks (as much as $100,000), although these normal clocks are at least 300,000 times more inaccurate.

Over time, it is expected that the prices of atomic clocks will come down so that eventually all GPS can have them installed for greater accuracy.

⚡ Differential GPS

The Evolution Of GPS | Differential GPS

Differential GPS (DGPS) makes the accuracy of a location more precise. Error in the calculation is rectified by the use of fixed GPS that transmit their exact location and make comparisons with the information received from satellites about their position. This allows your GPS to make the necessary adjustments to its own calculations, provided it can log into the DGPS. Again, the cost is a factor in only planes currently having access to DGPS.

Knowing the history and workings of GPS can only increase our pleasure and confidence in its use.

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