In my last article I discussed how the Global Positioning System (GPS) works and how it has changed navigation. GPS utilizes a set of 24 or more orbiting satellites broadcasting a coded signal that is used by a ground receiver to pinpoint location, speed, and distance while moving. I would like to delve into the numerous receivers available on the market to the civilian user. Essentially there are four types of receivers available.

The first is the military model. This operates on entirely different frequency than their civilian counterparts. The very accurate military units are on what is known as the P-code and Y-code and should be accurate within a foot or so. They include mapping features similar to consumer models.

The second type is surveying/Geographic Information System (GIS) models. Quite a bit larger than consumer models, they can easily be the size of a small briefcase. They are accurate to within one centimeter. This accuracy is obtained after being in the field through post-processing. The data gathered is stored and analyzed in a lab to compensate for atmospheric errors from the satellites.

The third type, for commercial transportation, is used to navigate ships at sea and aircraft. Often these units are tied into an autopilot system used to maneuver the vehicle. The units are quite large and permanently installed in the control panels of the vehicle.

The fourth type, consumer models, will be the focus of this discussion. The consumer model GPS unit can be permanently installed in a car or be handheld. There are units designed for joggers and bikers, those specifically for boating, and hiking models as well.

There are literally hundreds of different models available for you to choose from. The very basic models start at approximately $100 and go up from there. Some characteristics are common to almost all GPS receivers. They are able to store a waypoint, which is a location defined by its latitude and longitude marked in the unit's memory. All have a display screen that may contain a digital map and a back light. They also are able to tell you the time, location in coordinates, speed, and distance from waypoints. Some are able to connect to a computer to transfer data, and some display altitude.

Beyond these basic functions is where choosing a receiver can be a mind-boggling mess. The activity you want a GPS for will determine which features to look for. There are three major manufacturers of GPS receivers: Garmin (www.garmin.com), Magellan (www.magellangps.com), and Lowrance (www.lowrance.com). All three of these companies make good products. Garmin has the largest market share with Magellan in second place. Often the brand loyalty of the owners is akin to the IBM and Macintosh debate. But regardless of the differences, all the units operate in much the same manner and it comes down to personal preference more than anything else. The manufacturers have similar products to each other and are reliable and rugged. Most of these models that are designed for outdoor use are, as a result of their intended use, built very well. Most handheld models are waterproof and shock proof.

My receiver is made by Garmin. The model is GPSMAP 60c (www.garmin.com/products/gpsmap60c/). It is a bit larger than a cell phone and has a color display. This model runs on 2 AA batteries - you'll find that most handheld models run on 2 or 4 AA batteries. With normal usage, I can get about 30 hours of use with my rechargeable batteries. The unit has an external power cord that can be plugged into a cigarette lighter socket to save on those batteries. This model is a mapping unit, so I can upload maps to it and display my location on that map. Additionally, this unit supports auto-routing, which is a feature that allows the unit to give you turn-by-turn directions on the road.

With most units there are some basic features that you should be aware of. First the display screen has several different modes for display. The most common is a satellite page. This displays the satellites in graphical format. As you can see, the satellites are numbered and the ones brightly colored are those the unit is currently receiving a signal from. The bars below show signal strength and status. The higher the bar is the better the signal. The bars that are solidly colored indicate that the unit has locked onto the satellite. The outlined bars indicate the unit is receiving the signal but has not locked onto it yet. This screen in particular displays the latitude and longitude coordinates. Just to left of those coordinates, the accuracy of the unit is displayed. The gray sphere with a red center shows the direction the unit is currently moving.

The next screen shown is also in most models. It is the waypoint management screen. Waypoints are a location in the real world stored in the unit as latitude and longitude, thus allowing you to locate a place to go or show distance from. This image shows the names of some waypoints I have stored in my unit. They can be listed either alphabetically or by proximity. As you can see by the highlighted point, the unit also displays its direction and distance to the selected point.

After selecting the name and hitting enter, the details of the waypoint are displayed. It shows its coordinates and elevation. The highlighted "CAR" point is located in Grand Canyon National park just as I was beginning a hike. Click on this link to see a map. This screen displays the symbol I have selected as well as the direction and distance from the current location. I have options to delete the point, display it on the map, and navigate to it.

If I were to navigate to it, I would get this screen. The giant arrow points to the destination and of course the distance is displayed. The new item we see here is the speed. If I was moving when this picture was taken, you would also see the time it would take to reach the waypoint.

Across the top are several icons. These items are from left to right, the battery strength, 3D navigation status, USB connection status, and backlight status. The 3D navigation is particular to this model. It indicates that the receiver is getting a strong enough signal to find altitude as well as latitude and longitude. The arrow and compass move as the unit moves. As it is now, you would have to change your direction to the left a bit to head directly to the CAR waypoint. If you were to be moving away from the waypoint, the arrow would point down and the 12 would be at the top showing your heading as 120°.

The next screen displayed is the map screen. This is showing the current location of the unit with a white arrow. The pink line going in the NW direction is the direction to the waypoint, and the line to the waypoint is a little to the left of where the arrow is pointing. The red line is a track or trail. The track displays where the unit has moved. In this case it came down the street to my home. As you can see, it looks like I was driving in my neighbors' yards. The black lines are the streets and in this case the black blotches are ponds. The accuracy of unit displayed me off the street when in actuality I never left the road until I pulled in my driveway. In the lower left is the scale of the map. Above the map is data that was shown on the previous screen. The data above the map can be hidden as to provide a bigger map area on the display.

The GPS is also able to keep a travel log. As you look at the next screen, you can really get an idea of what kind of data the unit gathers. It has a trip meter and odometer. Also it keeps track of moving data. The max speed the unit has read is displayed. The moving time is blank as this data was gathered on a long trip and eventually it surpassed the field's ability to display. The moving average and overall average speed are great features. Before I had the GPS I would often occupy my mind while driving trying to figure out these very same averages. I doubt I ever got this precise. Elevation is also displayed.

Another useful feature of most GPS receivers is routing. Routing is the ability to string together waypoints to form a path. For example look at the next screen shot. In this route are several points within a preplanned trip. From here in Tampa Bay we are going to St. Louis, Missouri. Each point defines a leg of the trip. When you navigate this route, the first point that the GPS directs you to is Atlanta. When you get to Atlanta, it changes the destination to Chattanooga. This continues until you have arrived at your destination. This is a great feature for driving as it allows you to keep updating the GPS with the correct directions but frees you from having to manipulate the GPS while driving. Most receivers show you destinations in a straight line, "as the crow flies." A few of the more expensive units, such as this one, can auto-route. Auto-routing is a feature that navigates along roads loaded into the map as opposed to an as-the-crow-flies path. It displays turn-by-turn directions to your destination so that all you have to do is input the final destination. The unit then tells you which highways to get on and where to get off.

So how do you know what unit to buy? There are literally hundreds of different models to choose from. The unit that is right for you depends entirely on what you're going to use it for. If you primarily want it to navigate a boat, airplane, or car there are large screen models that run off the vehicle's electrical system and permanently mount to the console. If you want it to go hiking there are handheld models that can load topographic maps. The models range from very simple receivers that just stream data to large display models that can talk and direct you to the next exit verbally. Additionally there are other features like removable memory cards that map information can be loaded on. For a good place to find models available take a look to Joe Mehaffey, Jack Yeazel, and Dale Depriest's www.gpsinformation.net site.

If you would like to try a GPS without purchasing a unit, go to Lowrance's www.lowrance.com/software/pcsoftware/demos.asp site for a GPS simulator. They are listed by model and will install software on your machine. Although this will not actually lock onto satellites, it offers a great way to get a feel for their features and how they work.

So now you're interested, right? But what would need one these things for? Just to give you an idea of the many uses:

• Find your exact location on a map
• Find where you left the car
• Use to find your way back after getting lost in the woods
• Tie it to the dog and see where he goes at night
• Mark that great fishing spot
• Find out where the cruise ship or airplane you're on is
• Calibrate your speedometer
• Tell exactly how long to you get there
• Use it a trip meter
• Use it as a compass (when moving)
• It's fun to use

As you see there are tons of ways to amuse yourself. One of my favorite pastimes with the GPS is Geocaching (www.geocaching.com). This is a scavenger hunt with a GPS. A box is hidden in an interesting location like a city park. Inside a weather-proof box is a logbook and some trinkets. The coordinates of the "cache" are posted on the website providing details on the type of box, terrain, and notes from prior hunters. Because the GPS is only accurate within 10 feet or so, the cache can be quite difficult to locate.

Once found, you sign the logbook and exchange an item inside for one that you brought. The item is often of little monetary value. I often bring matchbox cars or maybe spare batteries for the GPS. Click on the link for the site and enter you're zip code and check out how many are near you!

In addition to the using the receivers as stand-alone units almost all of them can tie into your computer to expand its capabilities. Next month I will show you all the programs that are available to you and some great resources on the web for maps and waypoints.

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