GPS And Line Of Sight
How do they work? And why do they sometimes not work? GPS units rely on the 32* GPS (Global Positioning System) satellites that continuously circumnavigate the Earth and a mathematical calculation called trilateration (not triangulation). GPS receivers determine your exact location on our planet by analyzing how long it takes for the coded signals from at least three satellites to reach them. If the signals are blocked for some reason, the calculations can’t occur. Such blackouts are usually temporary and happen most often in large cities with tall buildings.
*Number of satellites: tycho.usno.navy.mil/gpscurr.html
The Garmin Oregon 550 provides a full set of features in an easy-to-use package at an affordable price. The waterproof color touch-screen affords intuitive navigation while the three-axis, tilt-compensating compass keeps you headed in the right direction. The Oregon 550 is preloaded with a Digital Elevation Mapping (DEM) basemap. The DEM shades the map elevations so it’s easier to discern points of reference based on the altitudinal differences depicted on the LCD. The Oregon 550 stores 1,000 waypoints, 50 routes and 10,000 track logs, adequate for most outdoor enthusiasts. Memory can be expanded via microSD cards. While most serious photographers won’t be warmed by the built-in, 3.2-megapixel digital camera, it’s useful for snapping waypoints because of the automatic geotagging feature. It also displays pictures stored on your media card. MSRP: $499.
Built with the avid hiker in mind, the Garmin Dakota 20 is compact, yet features a large, 2.6-inch color touch-screen and other full-sized features, including a high-sensitivity GPS with HotFix satellite prediction, barometric altimeter, three-axis electronic compass and microSD card slot. The compass shows where you’re headed even when you’re not moving or holding the device level. It includes a barometric altimeter that tracks changes in pressure and optionally plots the trend of change over time, allowing you to stay one step ahead of foul weather.
It also has a high-sensitivity, WAAS (Wide Area Augmentation System)-enabled GPS receiver with HotFix satellite prediction. The WAAS enhancement can improve location accuracy by up to a factor of five. The Dakota 20 offers paperless geocaching, which enables you to download up to 2,000 caches with information such as location, terrain and descriptions. It comes with a worldwide basemap. Other Garmin topographic, marine and road maps are available on microSD. The Dakota 20 can be connected to the Internet via your computer so you can track activities on Google Earth. MSRP: $349.
DeLorme Earthmate PN-60w
What do you get when you wrap all of the famous DeLorme street and topo maps together with the ability to type and send one-way text messages via the SPOT satellite system and package it in a rugged handheld GPS? You get the DeLorme Earthmate PN-60w with SPOT Satellite Communicator, a world-class location/communication device. You go places where cellular coverage doesn’t exist. With the Earthmate PN-60w, you can send text messages, post messages on Facebook and Twitter, and allow others to track your progress on Google Maps (tracking is automatic as long as the SPOT Satellite Communicator is active). In an emergency, you can send an SOS with a text explanation of your situation to ensure the best possible outcome. With the Earthmate PN-60w, you’re never alone unless you want to be. MSRP: $450.