Using GPS

I recently began to use the Magellan 4000XL GPS (Global Positioning System) unit and I am most impressed. This handheld GPS unit provides much more information than simply your position on the planet, though that feature is the most commonly used. The GPS provides your location, anywhere on the planet, based on triangulation of the unit and several of the twenty-four satellites that revolve around the earth.

When I initially turned on the 4000XL, I had to initialize it by entering my approximate latitude and longitude as well as the current date and time. With that information, the GPS unit was able to track the satellites overhead and provide me with almost precise location, an approximate elevation, and very accurate time. The reason that my location is not exact as displayed on the unit is due to Selective Availability (SA). The GPS satellites are owned and operated by the U.S. Department of Defense. SA keeps the GPS units from being precise due to security issues. Once the military determines how to foil an enemy's use of GPS, SA remains turned on for civilians. The general error is less than 100 meters, still precise enough for most uses on this planet.

The GPS not only provides location in latitude and longitude, it can also display location in other coordinate systems such as UTM, Irish, and Finish coordinate systems. The unit has an internal almanac for exact sunrise, sunset, and moon phase, all based on location on the planet and correct time.

Using the unit to help you navigate to a place is easy. The other day I visited my friend Don. Before leaving, I entered in Don's latitude and longitude (by converting his address in the Finding Places category of Net Links). The GPS unit immediately told me that I was precisely 63.8 miles from my destination and that I needed to head 142 degrees (approximately southeast) to arrive.

I began to drive towards Don's house and was able to track my speed in the car, my current heading (and how close I was to the bearing I needed to head), as well as the miles and estimated time of arrival to my destination. A built-in mapping feature tracked my path and indicated Don's house with a small flag. Other landmarks I had previously entered (such as campus, the mall, etc.) were indicated with dots. While the unit doesn't take traffic into account, I ultimately arrived at my destination and found that the coordinates I had entered were approximately a tenth of a mile off so I input a new latitude and longitude as the (approximately) correct location for Don's house.

Four AA batteries operate the unit for 24 hours. The Magellan includes a back-lit function that remains illuminated until turned off. An internal odometer keeps track of total and trip mileage.

While the navigation functions would be most impressive and useful if one were flying or taking a completely straight road to one's destination, the 4000 XL is an excellent navigation device and geographic tool. There are dozens of features that I have yet to explore but I'm already satisfied with the unit and its usefulness.

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