The next generation may never know the comedy of this stereotype: The wife pleading with her husband to please just stop and ask directions, while he refuses and drives on aimlessly with one eye on a tattered map and the other on a sinking gas gauge. That's because navigation systems that were once only offered in airplanes and luxury vehicles have matured into a pretty darn accurate technology within the reach of just about everyone.We thought it was about time for us to revisit Global Positioning System (GPS) technology, do a bit of explaining regarding the technology, and review the industry features and options in both built-in and portable nav systems for your 4x4. We also reviewed a serious GPS system for extreme off-pavement use, the Lowrance HDS-5 Baja. (See "Chartplotter" on page 67.)
There are quite a few variations of GPS receivers, each for a specific type of use. One of the earliest types was meant for hiking. Essentially a high-tech compass with a memory, these GPS receivers gave you compass readings. You could set a bearing and determine if you were staying on that bearing, and correct your direction as needed. You could save waypoints. These would be important markers along the trail, and could also be used to set your start and finish locations. These types of GPS receivers are still available, and are subdivided into general on-land use, freshwater maps for inland boating, and salt-water maps for coastal boating.
Unlike one made for hiking or boating, an in-dash or portable car navigation unit will have road-map data. In addition to showing you where you are, you can type in a destination, choose from a pre-loaded list of Points of Interest (POI), and the system will guide you to your desired destination. Depending on the model, it will also tell you most of the data that GPS receiver designed for hiking or boating will.
How It Works
First, it's helpful to understand how your navigation system knows where you are. A nav unit is a Global Positioning System (GPS) receiver; it receives information from satellites. There are 27 GPS satellites orbiting the earth in patterns that supposedly ensure that four are always "visible" by GPS receivers. This system was originally developed by the U.S. military, but is open for anyone to access now. By comparing distance information from at least three satellites, your nav unit can determine where you are on the Earth. It then compares that information with map data that has been loaded, and figures out where you are on the map. It can also determine your altitude, speed, and direction.
When GPS receivers first became available to consumers, they were large compared to today's models and not extremely accurate. Very detailed and accurate map data didn't exist for every mile of the modern world, either. As with most technology, size has decreased and accuracy has increased greatly over the past 20 years. Many nav units have multiple GPS receivers built in for faster accumulation of data, and they make use of the advances in computer power to make routing and rerouting calculations much faster.
When you enter a destination or search for a POI, the navigation unit searches a database that has been loaded into the unit. Then it uses GPS info to determine where you are, access map data also saved in memory, and calculates a route to take you from your current position to your destination. In nearly all of the navigation units, you can select your preferences for a route, such as the shortest, toll roads to avoid, and so on. Some of the newest models have real-time traffic updates for the major U.S. metropolitan areas, and can reroute you if there are significant traffic delays.