When you reach your final destination, your GPS receiver can optionally use the track log to help you navigate back to your starting point by using the track data to guide you retracing your steps. Check your user manual for model specific instructions on how to do this. Tracks are probably one of the most useful GPS receiver features if you’re working with digital maps. From a number of free and commercial mapping programs, you can overlay your tracks on top of a map to see exactly where you’ve been. The picture below shows an example of track data collected during a trail run and then uploaded to a mapping program.
Remember the story of Hansel and Gretel, the kids who dropped breadcrumbs in the forest to try to find their way back home? Their story would’ve had a different ending if they had a GPS receiver because all newer GPS receivers leave electronic breadcrumbs (called tracks or trails depending on the manufacturer) while you travel. Every so often, the GPS receiver saves the coordinates of the current position to memory. This series of tracks is a track log or track history. (Because various GPS models handle tracks differently, check your user manual for specific details.)
Note these differences between tracks and waypoints:
Names and symbols: Although tracks and waypoints are both location data points, tracks don’t have names or symbols associated with them and can’t be edited in the GPS receiver.
Autocreation: Unlike waypoints — that you need to manually enter — tracks are automatically created whenever a GPS receiver is turned on (that is, if you have the track feature enabled).
If track logging is enabled, tracks are shown on the GPS receiver’s map page while you move, like a trail of breadcrumbs. The GPS receiver constantly collects tracks while it’s powered on, so you need to clear the current track log before you start a new trip. If you want, you can save a current track log.
If you turn your Personal GPS tracker off or if you lose satellite reception, the GPS receiver stops recording tracks. When it’s turned back on again or good satellite coverage resumes, the GPS receiver continues recording tracks, but it will assume that you traveled in a straight line between the last track location saved, before satellite reception was lost, and your current position. Some GPS receivers allow you to set how often tracks are saved, either by time or distance intervals. For example, you could specify that a track be saved every minute or each time that you travel a tenth of a mile. Leaving the default, automatic setting for track collection should work for most occasions. However, if you’re using your GPS receiver for specialized purposes (such as mapping a trail), you may want to experiment with different intervals to give you the level of detail that you need.
You won’t find any standards when it comes to GPS receiver waypoint, route, and track formats. Each GPS receiver manufacturer seems to have its own data format. To further complicate things, software companies that make mapping programs also use their own data formats. This can make exchanging GPS data between different receivers and software a very big challenge. In order to help address this, the folks at topoGraphix, a GPS and map software company, developed GPX. GPX stands for GPS Exchange, which is a lightweight, XML (eXtensible Markup Language) data format for exchanging waypoints, routes, and tracks between applications and Web services on the Internet. GPX is slowly building up momentum and is being adopted by both software vendors and Web service providers. However, until a standard is widely adopted (and I’m personally not holding my breath), your best bet to exchange GPS data is the free GPSBabel utility. This versatile program converts information created by one type of GPS receiver or software program into formats that can be read by others. GPSBabel is available for a number of different operating systems as a command line utility, and you can find easy-touse Windows front-ends if you prefer a mouse and menus.
Depending on the model, personal tracking device can store between 1,000 and 10,000 tracks and up to 10 track logs. If you exceed the maximum number of tracks, the GPS receiver will either stop collecting tracks or begin overwriting the oldest tracks that were collected first with the most current ones. (Some GPS receivers let you define what action to take.) The number of tracks collected over time depends completely on your activity, speed, GPS coverage, and the GPS receiver’s track setting. Just to give you a ballpark idea, when I go trail running with a Garmin Geko 201, the receiver typically collects around 250 tracks an hour on its default track setting.
Some tracking devices for people reduce the number of tracks in saved track logs. For example, if you have 5,100 track points in the active track log, the number might be reduced to 750 track points when you save the log. This is done to save memory. You’ll still have a general sense of where you’ve been, but you lose detail. If you need a high level of detail — such as if you were mapping a trail — always download the active track log to a computer first before saving the track log to your GPS receiver. You can download waypoints, routes, and tracks to your personal computer. The data can then be stored on your hard drive, used with digital mapping programs, or loaded into other GPS receivers. You can also upload waypoints, routes, and tracks that you create on your computer to your GPS receiver. See Chapter 9 for tips on how to interface your GPS receiver to a computer.