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Sattelite navigation? in the palm of your hand? surely not!
Only two years ago your scepticism would have been justified, but technology has advanced rapidly during that time and it is now possible to get a range of gps devices at a much more reasonable price. This particluar review is (obviously) on the Garmin eTrex hand-held gps receiver, the cheapest in the eTrex family and a device aimed at the active outdoors type of a person.
But first things first... what is GPS? it stands for global positioning system and at it's simplest can be thought of as an array of satellites circling the earth, each sending out a time signal. GPS receivers pick up these signals and, from the difference between the times in the signal from different satellites, works out where on earth you are (literally).
GPS is surpsiingly accurate, down to about 20 feet on a good day, with the degree of accuracy depnding on how many satellites the receiver can pick up a signal from. It's worth pointing out that the satellite signals are not particularly strong so receivers only work when they have a clear view of the sky so around the city, along narrow streets or even under dense foliage, you may struggle. It is capable of measuring not only your lattitude and longitude but your altitude as well. Combine this with the ability to take snapshots of your location while you are travelling and you have a device that is capable of tracking your route in 3 dimensions as you travel.
The basics of GPS covered, what good is a hand-held receiver like the Garmin eTrex? Now is probably as good a time as any to give a brief description of the unit. It's about the size of an older mobile phone, measuring 11cm x 5xm x 3cm. It doesn't weigh much more either. The body is made of a tough yellow plastic and it takes 2 aa batteries which provide for about 20 hours of use. The front of the unit is dominated by the large lcd screen, (3cm x 5.5cm), which occupies the bottom two thirds. The top third of the front displays the etrex logo and covers the GPS antenna which needs to have a clear view of the sky. The sides of the unit contain all the controls, sheathed in a waterproof rubber casing. The two buttons on the right hand side are the power/backlight button and the 'page-select' button. The function of the first is obvious, the second cycles through the various displays available. The left hand side sports 3 buttons, again sheathed in rubber to protect from the elements. The top two are 'up' and 'down' buttons, used to navigate around the eTrex interface. The third is a select button, used to choose the currently highlighted option. The positions of the button make it easy to use the device single-handed which comes in useful when you're trying to stop your hat being blown off with the other hand! Gloves don't present much of a probem either. On the back of the unit is the battery cover, a rubberised, waterproof affair much in keeping with the rest of the unit. Finally there is the PC interface, again concealed beneath a waterproof rubber cover. It is through this port that, using the PC interface cable (sold seperately) that you can upload and download routes to/from the GPS unit.
As far as the screens on the GPS are concerned, the first you see when you switch it on is a map of the sky, showing you which satellites the unit expects to be able to receive a signal from. Underneath this is a bar chart which lists all of the available satellites and the strength of the signal from each. Once the unit has confirmed it's coordinates and locked on to a strong signal from at least 4 satellites, it's ready to go.
Pressing the page-select button takes you to the next screen, the map screen. This page will display a map of your route so far , indicating where you have been and the direction in which you are heading. This map can be zoomed in and out to give more or less details. *** It's worth noting that this map ONLY shows the route you have actually travelled (along with any waypoints or features that you marked on it yourself). It does NOT give you any other detail and it is definitely NOT a substitute for a decent map and a compass. ***
The next screen on the list is the Compass screen, where you get a large digital representation of a compas, showing you which way you are most recently headed. *** It's important to note that the digital compass only shows you your LAST heading. It will NOT update itself if you stand in one place and spin round as the GPS receiver only works on differences in coordinates. *** At the bottom of the screen you can also cycle through various statistics relating to your current trip using the up/down buttons. This includes things such as your current, average and maximum speed, current altitude and total distance travelled.
Last on the list is the menu page. From here you are shown the time and date along with a battery indicator. It also provides you with a list of sub-menus which are chosen using the up/down and select buttons. The first of these sub-menus is the Mark menu which allows you to enter your current coordinates as a waypoint. It lets you set the name (up to 6 characters) and choose an icon from a pre-defined list. Once you are happy with the name and icon, you accept the waypoint and it is added to a list and will appear on the Map screen. The next sub-menu allows you to manage all of your waypoints, either choosing one to head for or deleting individual points (or the whole lot if you want to start from scratch). After the waypoint menu comes the Route menu, which allows you to make up routes using stored waypoints. To build a route you simply add waypoints to it. You can then choose to follow a route. After Routes comes the Tracks menu which gives you access to the track log which is essentiall a list of coordinate snapshots taken while the unit was switched on. Tracks can be saved into the units memory and once there, you can make use of the handy 'track-back' feature which will help you retrace your steps. Finally you get to the setup menu which allows you to set things like the time format, time zone, display contrast and backlight timer, the units in which things are measured and map datums.
All-in-all it's a reasonably sophisticated piece of kit for your money, all well packaged in a sturdy impact and waterproof case. From it's appearance it's obviously aimed at people who spend a bit of time out and about. I use it when I'm out on hiking or biking. Set a waypoint where you parked the car and at strategic points along the way add some more (usually where there's a landmark or something similar) and should the worst happen you can use it to find your way back. This came in particularly useful on a recent trip to the Lake District when the cloud descended very suddenly leaving me with no visible landmarks and precious little hope of finding my way off the moors I was on. Fortunately, as I had used the GPS to track my way up the moors I was able to use the trackback eature to guide me back along the path I had taken and down to below cloud level without incident. As a test I even used it to take me back to the car and it was dead on. Suffice to say I was suitably chuffed.
*** Another safety reminder at this stage, a GPS should NOT be used as a substitute for a proper map and compass. It should always be used alongside these tools to aid and improve your situation, never on it's own. There are situations when GPS is all you have to go by, such as when the cloud descends and you have nothing to take a bearing from in which case it can be extremely handy, but remember that they are only accurate to within 20 feet at best so don't rely on them completely, especially if you're anywhere near any big drops or other hazards.***
Being able to find out where you have been is one thing, but the other beauty of GPS is the ability to give it pre-defined routes and let it tell you where you need to go. As GPS becomes more widespread, businesses are starting up that provide mapping information. This ranges from digitised OS maps and software that you can use to build a road route to routes that people have recorded on their GPS and downloaded for other peoples reference. A good example of the latter is mountain bike routes. A slowly increasing number of websites are offering GPS coordinates files for routes around the country. As always you shouldn't blindly trust them, but it's a good starting point. I certainly saved some of my recorded walks in the Lake District for future reference and next time I will probably take notes along the way (along with photos etc) and post them on a website for others to use.
Accessories are available in the shape of cables to connect it to a PC, Cigarette lighter power cords and handlebar & dashboard mounts and I have found www.discountgps.co.uk to be the best place to order most of these.
GPS software is slowly becoming more widely available on the 'net too. Shareware programs include GPS Utility (http://www.gpsu.co.uk). The best commercial program available at the moment is probably Memory Map Navigator (http://www.memory-map.com/) but at £100 for the software and £25 per OS map it's pretty expensive.
Once you have some GPS software, a whole other dimension opens up. Not only can you plan your walks in advance, you can record where you ACTUALLY went, how long it took etc, etc. These can be plotted on to maps and saved for future reference.
So to wrap up then, when you first look at it you may well think that it's just another gadget. However scratch a bit deeper and you will find that if you do a lot of walking/bike riding etc. it actually offers a reasonable amount of functionality from a package the size of a mobile phone and anything that gives you a little extra help can't be a bad thing.
If I were to pick any failings in the device it would be the limited memory. The base eTrex will only store one route made up of a maximum of 50 waypoints. While this is enough for a long day's walking (provided it's carefully planned), the larger capcity of some of the higher models (like the marvellous eTrex Summit) offer significantly better options around planning escape routes etc.
[Originally posted on DooYoo.co.uk (by me) back in May of 2002. Minor changes to wording during the port to Ciao]