GPX Guide
Route files and GPS advice

Accompanying a number of CTC trip reports are files that record waypoints and track logs for the trip. Currently these files are in GPX format, a light-weight XML data format for the interchange of GPS data (waypoints, routes, and tracks) between applications and Web services on the Internet.

GPX files can be processed by a number of applications (see the GPX web site for details). TUMONZ, The Ultimate Map of New Zealand, can import GPX files. There is also a piece of software available that transfers GPX files to various models of GPS. The sections that follow give details of the loader program (and a link to use to download it), advice on navigating using a track log loaded into a GPS, and some helpful information on using your GPS in the hills.

GPSLoader

GPSLoader is written by club member Doug Forster, and is freely downloadale and redistributable. It can download GPX and XMLF files (another GPS track log format) into GPS units. To install this program:

  1. Download it to your computer. Current version is version 3.0.
  2. Run the program you just downloaded, then click on Unzip and when finished click Close.

The program is a self extracting zip file that places two files in C:\Program Files\GPSLoader. You may wish to place a shortcut to GPSLoader.exe onto your desktop or Start menu.

To run the program simply start it by double clicking. Make sure your GPS is connected to your computer in the usual way and click Load. The program will then display a file dialog for you to select the .xmlf file you wish to load into the GPS. The program will search both USB and serial ports for a connected GPS.

Navigating using a track log loaded into a GPS

There are several ways and it depends a bit on what kind of GPS you have. Below is the suggested way of using the basic yellow Etrex that many people have.

Here it is assumed you have loaded a track log that is near to the route you wish to follow and that you are about to start off and are currently near the start. Turn on your GPS and wait for it to locate itself. Go to the tracks menu and select the one you are intending to follow. Then select TracBack. Then page the device until you are at the map screen and then press the scale in button until the current scale figure displayed is round about 80m. It is suggested that you set the map screen option to Track up rather than North, as after you have been moving for a while the map will then orientate itself in the direction you are going. Then you can immediately see if you are moving in the wrong direction because the track ahead on the screen will swing left or right. This is a fairly intuitive way of using a GPS in the tramping situation and if the track log has some intermediate waypoints loaded you can observe your progress directly on the screen.

It is suggested that you always have your GPS turned on when tramping even if the conditions do not require its use for navigation. That way you have a recorded track log on the screen that you can compare with your target track if you should happen to find yourself not where you thought you were. Some folks only turn the GPS on when they get into trouble. This is often too late as you might be in a no reception area or worse still in a spot with multi-path errors.

If you have a mapping quality GPS you can navigate in this way without going into TracBack mode. The map screen on these devices simply displays all your loaded tracks and waypoints as well as your current track. With a map program you can build up quite a few relevant map details to display on screen. Unfortunately the cheaper devices will only display the single track you are navigating plus any nearby waypoints.

Tips on using GPS units in the hills
  • Multi-path errors are probably the biggest gotcha using GPS units. A GPS requires at least 3 and preferably 4 satellites to locate its position. GPS signals do not penetrate even a small amount of dense material--your hand is enough to block the signal. There is no problem achieving this on open tops or other country with plenty of sky view, but once you get into a narrow valley or into dense bush the number of available satellites is greatly reduced. If the number is reduced to less than 3 there is no problem--the GPS simply reports that it doesn't know where it is. However sometimes a satellite may be just below the horizon but be bouncing its signal off an opposite hillside or bluff. The GPS assumes the signal is line of sight and calculates your position as if you were at the corresponding distance beyond the reflecting object. If the GPS has enough "real" satellites it can detect this situation but if it only has three is will just blindly give the wrong answer.

    If you are in an area like a deep valley or gully or in dense bush or reception is coming and going all the time, page your device around to the satellite screen occasionally and take a peek at how many dark bars are showing. If there are only three then start applying some traditional navigation skills immediately. If there are four showing then you might be a bit sceptical, but more that than and it is probably telling the truth.

    The newer colour GPS units seem to have better receivers and this problem is somewhat reduced especially if you have a model to which you can attach an external aerial.

  • If you are recording but not otherwise using your GPS put it at the top of the top pocket of your pack (or higher if you can figure out how). Your body will completely block the signal for a large proportion of the sky view if you place it low down. By the same token do not put it in your pocket or on a waist clip.

  • If you want to record tracks do not do it by saving the active log as a track log unless you have to because you are out of memory. For some reason Garmin GPS units throw away the time stamp when you do this and the time stamp is probably the most useful thing that comes from a log.

  • A PDA screen protector over a GPS screen saves the screen from getting scratched by the inevitable swipes from scrub and branches. If you can make a small container pouch that straps onto the wrist you have your hands free but can still observe the GPS screen when needed.

  • Rechargeable batteries work well in a GPS. You can now get 2500maH NiMh rechargeable AA batteries and that is not far short of the capacity of throwaway batteries. You can now buy ones that come precharged and these are strongly recommended as they don't leak charge like the older ones. They're great for torches, too.

Thanks to Doug Forster for providing most of the material on this page.