Handheld GPS Basics

Satellites

• Basically, a handheld GPS unit captures satellite signals from 24 satellites orbiting the Earth and monitored by the U.S. Military. To define a position, the GPS unit interprets through triangulation. For accuracy, this requires that your GPS unit is able to detect the signals of three satellites. The satellites are in a constant 11,000-mile orbit around the Earth. The actual position is calculated from distance measurements to the satellites.

Accuracy

• Many factors can affect the accuracy of positioning, some of which you can control. The greater number of satellites that your handheld can detect, the better the accuracy. Topography and heavy tree cover, for example, can impede detection of satellite signals. Likewise, buildings can also interfere with reception. Environmental factors such as heavy cloud cover can degrade reception. Bearing such factors in mind when using your GPS unit can improve the accuracy of your reading.

  Careful selection of a handheld GPS unit is another way to ensure better accuracy. Units manufactured today use the GPS receiver chips called SiRFstarIII from SiRF. Newer units feature hardware upgrades as well as new GPS technology such as WAAS, or Wide Area Augmentation Service. This new technology aims to increase GPS accuracy by improving the integrity of satellite signals and correcting for bad signal information. Most modern handheld GPS units do not require a separate receiver.

Maps

• To get the most out of your GPS unit, you will need to be able to read maps and understand some basic terminology. Positioning requires the use of a grid. Two common types are the more familiar Latitude/Longitude (Lat/Long) grid and the Universal Transverse Mercator (UTM) grid. With the Latitude/Longitude system, a position is detected by angular measurement on two axes. The latitude is determined by the north/south position above or below the Equator. The longitude is determined by the east/west position in reference to the Prime Meridian. Positions are based on degrees.

  The UTM system is metric-based, with positions based on a referenced 60-zone grid.

In the Field

• A handheld GPS unit uses waypoints to mark positions. Accurate, descriptive naming of waypoints will make navigation easier. Rather than "waypoint1," name waypoints by description such as "trailhead" or "car." Waypoints can be created in the field or uploaded to the unit. A "Go To" feature will direct you to a given waypoint. Navigation is possible with a displayed compass and navigating factors such as distance and direction. Because conditions may cause a GPS unit to react slowly to changes in position, always carry a compass when navigating. As you hone in on your waypoint, stop when you are within 100 feet. This will allow the signals to "catch up" with your position.

Recreation

• Handheld GPS units are useful tools not just for navigation, but for recreational purposes too. The use of GPS has also led to the sport of geocaching, basically a high-tech treasure hunt. Having some basic knowledge of GPS and navigation adds to the enjoyment and usefulness of handheld GPS units.