Where am I? GPS review tells all

Devices that use the Global Positioning System are getting as common as wireless phones were five years ago. GPS is invading the IT world in business, science and recreational applications, and we can't yet imagine how it will evolve in our daily lives.Just as there are many different ways to use GPS, there are many different products on the market for specific needs. Before you buy, remember that the right device for hiking across a field might be completely wrong for measuring highway distances.If a GPS receiver can see at least three of the Defense Department's global constellation of 28 Navstar satellites, it can calculate where it is in two dimensions'longitude and latitude.If the GPS receiver can see four or more satellites, it can also calculate altitude. That's pretty incredible when you consider that the Navstar satellites are about 12,000 miles up, whereas altitudes on the Earth's surface vary by only about 5.5 miles.In addition, a GPS receiver within reach of the Wide Area Augmentation System, or WAAS, can nail down its position to within about three meters on a clear day. WAAS aids aircraft in precision navigation and landings via a network of ground-based reference stations.But in bad weather or indoors, a GPS device might not be able to contact any satellites directly, so its readings could be off by a sizable fraction of a mile.What kind of GPS unit should you buy? The first question to answer is what you plan to do with the readings.Do you perform geological surveys? Map locations of species of flora? Carry out search-and-rescue operations during forest fires? Check highway distance indicators? The type of GPS device you need differs for each of those purposes.We tested four GPS devices for ease of use, adaptability and features. We clocked their acquisition times from the same place within the same couple of minutes'on a small field with limited horizon visibility and nearly cloudfree weather.Accuracy of the location displays was almost completely consistent across the devices, but acquisition times varied considerably.The Brunton Multi-Navigator worked best for overland navigation on foot, far from roads or landmarks. With no way of displaying the GPS information in map format, a user would either need to have a map or be in a familiar area.The feature that set the Multi-Navigator apart from the other devices was its compass-only setting. Display of just the compass extended battery life drastically from around 10 hours to something like 60 days'but only if the compass was on for a maximum of 15 seconds every five minutes or so.That feature might be a lifesaver for a user cut off from civilization and limited to a single pair of batteries.The Multi-Navigator was definitely no-frills, however. Encased in neoprene rubber, it lacked accessories such as a computer cable or map software. But because it could internally store up to 1,000 waypoints, or landmark coordinates, the user wouldn't need to download data to a computer except for a very large project.The Magellan SporTrak Pro seemed to be built for a different use entirely. The reasonably large map display would be perfect for users who travel mostly on foot or near roads or other landmarks.There were somewhat customizable screens to show map position, satellite status, compass direction and other data. That made the SporTrak Pro highly versatile for many different needs.Each time I powered it on, however, I got a warning screen that said, 'All data is provided for reference only. You assume full responsibility and risk when using this device.' If I didn't press OK within a short time, the device would power down.I suppose Magellan considers a disclaimer necessary, but it annoyed me nonetheless.Although you can buy street-level map software to load into the SporTrak Pro, the built-in map was highway-level. I found it difficult to reference roads, because if I weren't right next to a road, it wouldn't show in my area of the map. But I suppose that's just as well because the basic map wasn't the most current or accurate at smaller scales.Sometimes I would be standing on a road, and the device would say I was 100 meters away from the road. Signal lag conceivably could be at fault, but it was a notable discrepancy.Accuracy was fine at the 0.4-mile scale or larger, so it wasn't too much of an inconvenience. Just don't count on the SporTrak Pro for precise work where every meter counts.Users in search of extras should take a look at Magellan's SporTrak Color. In addition to all the features of the SporTrak Pro, the SporTrak Color had a color display, built-in electronic compass, thermometer and barometer. It also displayed the same annoying legal notice.Seeing the map in color did indeed make a difference in my comprehension. Instead of wondering what that gray-shaded area to the north might be, and having to change the scale to see the name, I could instantly tell by color whether it was a park or industrial center.Color also aided in telling types of roads apart, whereas line thickness was the only indicator of road type with the SporTrak Pro. It's amazing how useful color becomes when you have to do without it.The built-in compass should prove very useful. For example, a compass alone might get you through when you can't communicate with enough satellites for a reading'say, inside a cave. But the unit is always in GPS mode, so even if you wanted only a compass heading, the unit would still be draining its battery for satellite communication.The SporTrak Color's battery drain was greatest when displaying a map. You could turn the compass off and get a bearing from the satellites, but in that case, what's the point of having a compass? The extra battery drain from the compass, though not drastic, was noticeable.If battery life is a concern, the DeLorme Earthmate doesn't even use batteries. It plugs into a computer instead.My test unit had a Universal Serial Bus connection for a desktop or notebook computer. DeLorme representatives said an Earthmate that can connect to a handheld computer will be available soon.The need for a computer hookup means the Earthmate is best suited for vehicular jobs where there's no requirement to mark waypoints outside the car or truck.An accessory suction cup made the Earthmate convenient to operate inside a vehicle, securely attached to the dashboard.Because a notebook LCD is a lot bigger than a typical handheld screen, the Earthmate was far easier to reference when driving than other test units. The included software even had a high-contrast setting, so I could read the map in sun glare. This definitely would be the best device for drivers.The street-level map software was fairly detailed. But there was no built-in compass, probably because the designers realized most users would place the device right next to an iron engine block.Good functionality and very low price earned the Earthmate the GCN Lab's Bang for the Buck designation.Overall, I would say the SporTrak Color is the best general-purpose unit and also the one to buy for urban surveying. Other devices cost less, but the built-in features make the SporTrak Color worth the extra money.