Choosing a GPS receiver
These navigation gadgets are better than they've ever been. Get to grips with the jargon and decide which facilities you need.
Featured product: eTrex Vista CX
1. Do you need a GPS receiver?
GPS stands for 'Global Positioning System', which is a system of 27 earth-orbiting satellites developed by the United States. Data from these satellites can be used to determine any location on the globe when read by a GPS receiver. So if you want to know where you are (to an accuracy of 10-20m), a GPS receiver is for you.
It is particularly useful for navigating across large, featureless areas such as the Cairngorms and Pennines. It also provides a useful backup for when conventional map and compass techniques fail.
2. Receivers
GPS receivers use different numbers of channels to track the satellites. A 12 channel parallel receiver is now the most common. This is better than a 6 or 8 channel parallel receiver as it has more 'eyes on the sky' which allows it to find the satellites more easily, particularly in built-up areas or in woods. The better the receiver, the more chance there is that the unit will be able to make an accurate fix on your position.
3. Map Datums
Map datums describe the irregular shape of the Earth for a particular region. Different maps have different map datums because the Earth is shaped differently in different regions. So GPS users must reference their GPS receivers to their maps. What that means is that if you are going to use the GPS receiver abroad, you should make sure it has lots of map datums that you can set for use in other countries. In the UK the GPS receiver must be set to OSGB or GRB36. For most European countries you need European 1950 set as the datum.
4. Coordinate Systems
A grid of horizontal and vertical lines is provided on maps of the UK so that you can pinpoint a location with a grid reference. But the two most common coordinate systems in the world are LAT/LON and UTM. So if you are using a GPS receiver in the UK, you must set the coordinate system to one that matches the coordinate system on the maps you are using, which is usually referred to as OSGB, ord srvy GB, or British Grid. The factory setting for most GPS receivers is LAT/LON. If you are traveling abroad then make sure the unit has the appropriate coordinate systems for the map you are using
5. Compass
Although many GPS receivers boast a compass, it is not usually a magnetic compass. This means it cannot tell you in which direction to move until you start moving, at which point it tells you which direction to travel to reach your next waypoint. But you could have stepped over a cliff by then of course! A GPS receiver with a digital magnetic compass built in is therefore very useful as it will point you in the right direction before you start moving.
6. External Antenna
The ability to connect an external antenna is very handy if you want to track movements inside a car, as it will improve performance. Otherwise you will have to place the GPS receiver right under the front window to enable it to 'see' the sky and get a signal from the satellites. If you're walking this feature is not essential, but it's useful when driving to the start of a walk.
7. Computer Links
Way point upload/download capability is a must if you really get into using a GPS receiver for planning trips on a regular basis, as keying in waypoints manually is very slow. With a computer link-up you can download routes from your PC in a matter of seconds.
8. Power
External power capability is a nice feature if using a GPS receiver in a car. This can save lots of money on batteries. But on the hill you'll have to rely on battery power, so look for long battery life.
9. Waypoints
Waypoints are coordinates of a location. If you want to store lots of routes you'll need a big memory built into the GPS to handle all the waypoints. The more waypoints the GPS receiver can store, the more routes you can store in your GPS ready to use. The ability to store 500 waypoints is a good start point. Some manufacturers use the term 'points of interest' (POI) instead of 'waypoints' but they are the same thing.
10. Routes
It's useful to store a few routes plus a few escape routes or variations to each route into a
GPS receiver so you don't have to reload routes all the time. To be able to store 10 routes is good, but a capability to store more is even better for regular users.
Content provided by
