Monday, May 30, 2011

Handheld GPS Buyer's Guide

Before talking about the specific things to look for in a handheld GPS unit, it helps to understand a little bit about how the system works and a description of some of the commonly used technical terms used to describe their various features. So, here it goes:

The Global Positioning System (GPS) is a satellite-based system developed by the United States Department of Defense that provides precise time and location data by using a constellation of 30 satellites used for civilian GPS. They are called the Navigation Satellite Timing and Ranging (NAVSTAR) satellites or Global Navigation Satellite System (GNSS). Each satellite completes one Earth orbit every 12 hours, continuously transmitting its position and a time signal, which a GPS receiver can pick up. The handheld GPS units receive the transmitted data from four or more satellites in view to calculate a user's position, typically to within 50 to 100 feet.

Unfortunately, many factors can impact the receiver’s accuracy, including number of satellites in view, atmospheric conditions including bad weather, buildings, tunnels, mountains and heavy foliage. However, the latest high-sensitivity GPS receiver chips are able to all but do away with these issues, and this has become less of a concern then it used to be.

Most modern handheld GPS units use the Wide Area Augmentation System (WAAS). This system is based on a network of 25 ground-reference stations. Each station receives GPS satellite signals, corrects any errors, and then forwards corrected signals to a Wide Area Master Station, which makes some additional calculations and uploads the newly corrected data to a satellite. The message is finally broadcast on the same GPS frequency and picked up by GPS receivers capable of reading WAAS signals and that are within the broadcast coverage area of the WAAS. The difference in accuracy can be significant: a WAAS-enabled GPS receiver can fix your position to less than 10 feet. While that might not make a big difference if you're driving in a car, it's a big deal if you're hiking through the mountains trying to find your base camp, a path through the woods or trying to find a geo-cache.

Most handheld GPS units can store 500-1000 waypoints, which are coordinates for a selected location. You can enter waypoints while you're traveling, so you can find your way back or you can enter them before you leave home or camp to lead you to your next destination. These markers aid the unit in plotting the routes that interest you and provide you with a virtual breadcrumb trail.

Here's what to look for when considering a handheld GPS unit for your next hiking, backpacking, camping, hunting or geo-caching trip.

  • Determine the map set and degree of accuracy you will need. Different models come with different types of maps, and some map sets are more detailed than others.
  • Avoid unnecessary high-end features. You can save some money if you do not need features like a barometric altimeter, electronic compass, two way radios or heart-rate monitor, all of which are found in costly, top-end GPS receivers.
  • Waterproof/Water-Resistant handheld GPS receiver . As editors at GPSReview.net say, "The IPX-4 standard means that the device will stand up to water splashed on it from any angle. However, this does not mean you can drop it in a stream. For that you want a device that is IPX-7 waterproof." A unit that meets IPX-7 standards can withstand accidental dunks, but it isn't intended for swimming.
  • Twenty-route memory is standard, and some models can store as many as 50 routes. Make sure you get one with at least 20 routes. Keep in mind that GPS receivers with a memory-card slot offer expandable route memory. 
  • Look for at least 500 user-entered waypoints. Some units can store many more.
  • Check size and weight. This is a very personal thing, but you should consider it if you are thinking about hauling a unit around in the wilderness. Lighter units come at the expense of screen size.
  • Make sure the unit you are considering has a feature that guides you from waypoint to waypoint. This feature is essential for hiking use.
  • Look for a unit that uses a 12-channel parallel receiver system or better. This will give you the best reception in wooded areas. Some GPS units can receive even more channels.

The buyer's guide was originally posted on my website, but had several requests to share it here. Hopefully this list helps you find the perfect handheld GPS unit for your needs!
                                                      - Backcountry Gear @ Gear&Gadgetry

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