GPS for Dummies.pdf - Engineering Surveyor

Chapter 4: Grasping Important GPS Concepts81You won’t find any standards when it comes toGPS receiver waypoint, route, and track formats.Each GPS receiver manufacturer seemsto have its own data format. To further complicatethings, software companies that makemapping programs also use their own dataformats. This can make exchanging GPS databetween different receivers and software a verybig challenge.In order to help address this, the folks attopoGraphix (www.topographix.com), a GPSand 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 serviceson the Internet. GPX is slowly building upGPSBabelmomentum and is being adopted by both softwarevendors and Web service providers.However, until a standard is widely adopted(and I’m personally not holding my breath), yourbest bet to exchange GPS data is the freeGPSBabel utility. This versatile program convertsinformation created by one type of GPSreceiver or software program into formats thatcan be read by others. GPSBabel is available fora number of different operating systems as acommand line utility, and you can find easy-touseWindows front-ends if you prefer a mouseand menus.To get more information about GPSBabel anddownload the utility, visit http://gpsbabel.sourceforge.net.Depending on the model, GPS receivers can store between 1,000 and 10,000tracks 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 theoldest tracks that were collected first with the most current ones. (Some GPSreceivers let you define what action to take.) The number of tracks collectedover time depends completely on your activity, speed, GPS coverage, and theGPS receiver’s track setting. Just to give you a ballpark idea, when I go trailrunning with a Garmin Geko 201, the receiver typically collects around 250tracks an hour on its default track setting.Some GPS receivers reduce the number of tracks in saved track logs. Forexample, if you have 5,100 track points in the active track log, the numbermight be reduced to 750 track points when you save the log. This is done tosave memory. You’ll still have a general sense of where you’ve been, but youlose detail. If you need a high level of detail — such as if you were mapping atrail — always download the active track log to a computer first before savingthe 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 mappingprograms, 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.