What In the World is GPS?

Last Updated (Tuesday, 24 August 2010 10:12) Written by Raymond Nakamura

We just got a new toy — a GPS (Global Positioning System). It's not like we go anywhere, but my wife loves gadgets and I have a lousy sense of direction, so there you go. I'm not convinced of its usefulness, but I find the back story intriguing. 

On Your Mark

Let's say I've been given the address for a Tupperware party (do they still have those?). I turn on my GPS, which is a little bigger than a deck of cards (do they still have those?) I plug it into the power outlet formerly known as a cigarette lighter. The GPS model apparently works for walking as well, but so far I've only used it in the car. The GPS makes me agree not to fiddle with it while driving.

Map and Territory Problem

The maps are already in memory. The companies make more money off you by charging you to upgrade them. I was using my Dad's GPS a while back the screen blanked out when we reached a relatively new road like we were just floating in space. A bit disconcerting. 

Match Game

The GPS tries to figure out where in the world it is to match up with the data in its map. To figure out your position in two dimensions, you need to know the location and distance from at least three reference points (see below). 

Finding Your Place

The GPS is looking for its three-dimensional position (longitude, latitude, and altitude). It receives information about the position and distance of at least four GPS satellites (use your imagination — it would be too much work to draw). 

Twinkle, Twinkle Little Sat, How I Wonder Where You're At

To ensure access to at least four satellites accessible anywhere anytime, the United States Air Force has kindly placed more than twenty-four of them hurtling overhead at 240 km/hr, some 20,000 km above us (almost like travelling between Vancouver and St. John's, Newfoundland three times). Each orbits the earth twice a day, weighing as much as a compact car (1600 kgs).

Time and Space Continuum

To figure out distance, the GPS receiver uses time. Each satellite has an atomic clock onboard, synchronized with the central timekeeper to sixteen decimal places. They send out a high frequency, low-power radio signal able to carry information about its time and position and not be affected by atmospheric disturbances in the ionosphere or troposphere. Like all forms of electromagnetic radiation, these signals travel at the speed of light.

All Together Now

The receiver doesn't have its own atomic clock but it does get synchronized with the central timekeeper. It compares its own time with the time signal sent by each satellite. The difference between the time signal and its own time is related to how far away each satellite is. Initially, the U.S. government intentionally introduced timing errors so non-military GPS receivers were limited to an accuracy of about 100 meters. But in May 2000, this was eliminated and now consumer products can get from 10 to 2 metre accuracy. Mine can't seem to tell the difference between me parking in front of my house or driving into my garage behind. Military applications use an additional stationary receiver with a known location to increase precision to under a metre by correcting for errors in the satellite signals. 

My Way

We punch in the address for the Tupperware party. The GPS figures out the path, according to criteria we can adjust, like fastest, shortest, or least amount of gasoline burned. Our position continually gets updated so it can tell you your speed and how many minutes it will take to get to your destination. Having a voice tell you when to turn can be useful, although it can feel like having a backseat driver on your dashboard. At least the voice remains calm even when you make a wrong turn.

It can be distracting to watch the little screen instead of the road. If you're driving on your own, it can be startling when it suddenly speaks up if you haven't heard it in a while and drive without the radio on. The software for this continues to evolve. Some of them incorporate traffic information and construction sites. Mine doesn't have that, so I often take a different route from what it suggests. Still, sometimes it has suggestions I wouldn't have thought of that turn out to be useful. At other times, I realize just following instructions, I don't really know where I'm going. My biggest problem is not being able to see the big picture, so I'm never sure I can trust the directions. A bit metaphorical perhaps. My wife is usually the navigator and on a recent visit to the wilds of Port Moody, she noted that having a GPS made for a much more relaxing ride because she didn't have to worry about getting lost. Maybe we should take up geocaching, like the people in the Treasure! exhibit who have a game of looking for little treasures using their GPS.

Do you think GPS is the way to go?