This post follows on from the first in this little series, about choosing and using a GPS for mountain-biking. The first post was just a general overview. In next few articles I want to concentrate a bit more on some of the features of GPS devices. In this post I will start off the overview of GPS features with a look at the most basic functionality you can expect from a GPS device. In a later post I will try to compare some of the devices that are out there and share some more specific ideas about the practical application of these GPS features to mountain-biking.

Basic GPS features

1) Location, location, location

No surprises - this is the point of GPS. As described in the previous post, a GPS device uses satellites to determine your exact location on the earth, expressed in coordinates, longitude, latitude and elevation above sea-level (and not just in Serbia, despite the orientation of this blog)! . It also uses your movement to work out your direction and all GPS devices have a compass display. However only the more expensive models have a proper magnetic compass, so be aware of that.

However, if that’s ALL it does, then its use is going to be pretty limited. If all it did was display a couple of coordinates, most people could probably do no more than stare at these mysterious figures in bemusement.

With a basic device like that, though, like the entry-level Garmin eTrex, you can also save different locations, either as you travel around, or by keying them in if you have a map from which you can read coordinates - you’d need a pretty large-scale map for this to be anywhere near accurate! You can also use PC software to find the points you want on a digital map and then upload to the device. This is called making waypoints, all devices allow this, and it means that you can head for a previously-marked point, e.g. where you left the car! Or you could plot in major landmarks and then just use them for orientation. This in itself is pretty useful, and real afficionados might enjoy this shoestring approach to navigation, but I think most people are going to want a bit more help from their device than this!

2) Getting on track

A second feature which pretty much all GPS devices have is track recording. This means that the GPS records your location at regular intervals while you’re biking or hiking and plots this information on-screen as a series of dots or a line, giving you a representation of the route you have taken (though don’t confuse this with “routes”, which is something different, on Garmin devices at least, more in the next section). You can then follow this track back to your starting point, or to a point where you maybe made a wrong turn. Also you can upload the recorded track to the PC, where you can use more advanced programs to plot the route on a map, work out how far you went, how fast, etc.

Track plotting is limited to the amount of memory the device has on board. This might be a good point to explain about track recording and track saving on Garmin GPS devices, because it really isn’t explained very well in the instructions. The track log is the ongoing recording that your GPS makes, if you have turned recording on. It allows for up to 10,000 points to be recorded. These 10,000 points get eaten up until the memory is full, and then it will either start from the beginning, erasing the first points, or just stop, again depending on the setting. How far you can cycle, walk or drive before you fill the memory up depends on what recording mode you have used - a “hi-resolution” (my coining, it’s not generally called that) mode, or a lower setting.

Once you are finished, or have filled up the memory, you can save the track log to one of 10, 20 or more (depending on the model) empty slots, and then wipe the track log and start recording again. So the track log is just used for recording your current trip, the save slots for storing them. The big catch with saving your track log, though, and you won’t find anything about this in the manuals of Garmin devices (at least I haven’t been able to find it), is that the track save-slots have nowhere near the 10,000 points storage space that the track log does! In fact they typically only have space for 500 points! So how does it save your track log of 10,000 points to a space with 500 points? Good question! I have no idea! But I strongly suspect it drastically lowers the “resolution” of the file to do so. In fact it would have to lower it by a factor of 20! That is really bad, so we don’t want to use those save slots for serious GPS-ing. More about that when we get into specifics in a a later article.

But the good thing about a more expensive device, like the Garmin eTrex Vista Cx, (which I might as well tell you now is the device I am going to recommend to you in about 20 posts time! That’ll save you some time, won’t it!?) is that it can record direct to a micro-SD card and thus save practically unlimited amounts of data, in portable gpx format.

3) What are you routing for?

Garmin GPS’s also have something called routes. These are essentially a set of waypoints that you connect together, ideally on the PC software, to make a route which you can then download to the device and follow on-screen. They are quite limited - the basic Garmin eTrex only allow 125 waypoints per route, and 20 route. To be honest, I have not really figured out what use they are! You can achieve the same thing using tracks, which are much more flexible and have greater capacity. I am sure someone can tell me what routes offer that tracks don’t, but I haven’t yet discovered it.

End of part I

Those are some of the most basic features of GPS devices, particularly focusing on Garmin, I must confess. I think that’s enough to be getting along with. More features in an up-coming post, including trip computers, maps, and elevation profiles.

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Posted on July 7th, 2007 by markowe
Filed under: Biking - general, GPS