January 2001, Issue 126

Where's Waldo?
Pinpointing Location by Interfacing with a GPS Receiver

The term GPS (global positioning system) has lost its effect to raise eyebrows. There was a time when GPS was strictly a tool for guiding missiles toward their intended targets. The government, in its fundamental wisdom, allowed the military to add a secret fudge factor to GPS signals that produced errors in the accuracy of the system. If other countries used GPS data to aim their own missiles, they wouldn’t be hitting their targets. Of course, this means they would hit somewhere else, potentially in a heavily populated area. This might be fine from a military standpoint, but probably wouldn’t sit well with the people in that area.

Hand-held GPS devices have been in sporting goods stores for years. These early models couldn’t actually tell you your location, but merely allowed you to get back to where you started. Many of today’s hand-held devices also contain a map for true stand-alone position identification. Recently, GPS was introduced in conjunction with some of the higher priced automobiles (e.g., GM’s OnStar). Although more than just a GPS, the feature to pinpoint a car’s location for emergency service can be quite comforting, even if it comes with a monthly charge.

Those of us who are forced to look in the aftermarket for these accessories will find vehicle-mounted GPSs complete with downloadable area maps. You can download business, educational, governmental, recreational, and religious points of interest in addition to the road and highway systems. Most systems consist of hardware and software. The Street Atlas mapping software accepts input from the hardware GPS. Latitude and longitude are entered automatically and the correct map appears on the screen. The GPS can’t indicate a true direction unless you’re moving. Direction is calculated based on where you are and where you’ve been.