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Using a GPS for biking

By Joe Adnan

This article was written so that the reader can make full use of the GPS data given with the bike trail guides. It's not intended to be a comprehensive guide to using a GPS receiver. I've made specific reference to Garmin receivers because this is the brand that I'm familiar with. I expect that most other outdoor-use GPS receivers will work on the same principles and will have similar principal features.

What is it?

The Global Positioning System is a navigational system maintained by the US military comprising 24 satellites and numerous ground stations. These satellites communicate with a receiver, usually hand-held, to determine the receiver's position by triangulation. So, strictly speaking "GPS" refers to the whole system of satellites, ground stations and software operated by the US military; the handphone-like device that you stick onto your bike's handlebar is a GPS receiver. It's the best use of the US taxpayer's dollars (all 12 billion of them) that I can think of, and for that reason alone you should run to your nearest store to get one.

GPS and mountain biking

Accurate maps of trails in Malaysia are notoriously difficult to obtain, an unfortunate legacy of the Malayan Emergency. Today, you can buy 1:50,000 scale topographic maps of parts of Peninsular Malaysia from the Mapping and Survey Department. But these maps do not always indicate where biking trails exist, and often show trails that no longer exist. Using a GPS receiver, you can do your own mapping and share trail information with other trail users.

Where to get a GPS

In KL, the place to get GPS receivers is Advanced Equipment in Taman Maluri. They start at about RM800. If you were to ask me which GPS to get, I'd say: Garmin eTrex Venture. It's small, has most of the features that you'll need, omits all the features that you don't, and is relatively affordable for this last reason. Choosing a GPS to buy.

How to use the information on this site with a GPS: Manually entering waypoints

Of course, you'll have to read the manual that came with your unit. If you own a Garmin unit, Dale DePreist has an excellent on-line manual that betters Garmin's own. Once you've done so, you can check out one of the pages on this site that lists the trail route using latitude and longitude coordinates, such as the Sungai Dua trail.

Now, switch your GPS on. If your unit allows, set it to "gps off" or "demo mode" (eg on the newer Garmin eTrex units) or set it to "Simulator" (for the older units such as the Garmin GPS 12.) Doing so will save your batteries as it shuts off the receiver circuitry.

Then, save each of the waypoints in the table above into your GPS receiver. The simplest way to do this is:

Go to the main menu and select "waypoint".

  1. Select New from the 'on page' menu.
  2. Enter the new name and the lat/long entry. (Specify WGS 84 for the datum, lat/long for the coordinate system.)
  3. Select an icon, if your unit allows.
  4. Select done when you are finished.

Do this for all the waypoints in the table. Once you are done, take a print-out of the trail directions and route table with you on your ride. As you ride on the trail, you will pass each waypoint that you have saved. Used in conjunction with the written directions, you should be able to find your way around the trail.

Uploading Waypoints into your GPS receiver

You can also upload a waypoint file into your unit from your computer. I'll bet there are countless ways to do this, but I'll only describe the use of a GPS application called OziExplorer. Because that's the application I've used for the waypoint files found on this site and, more pertinently, that's the only way that I know how.

What OziExplorer does is to allow me to download the data that I've acquired on my GPS to my computer. Then you can download that data from this site and upload it into your GPS. Of course, it's also much more powerful than that; for example you can use OziExplorer to overlay the GPS data over a scanned map to generate your own trail map.

To use OziExplorer, you'll need, in addition to your GPS receiver:

  1. A non-obsolete PC with a free serial port. (Lots of RAM will be nice if you want to use scanned maps.)
  2. A cable connector that will allow you to link your GPS to that serial port. If you own an eTrex Venture/Vista/Legend, this should have been bundled together with your unit. If you don't have one, you can buy one from the supplier, or if you're an electronics whizz like Pat, you can make one for yourself and all your friends.

First, you need to install OziExplorer. A shareware, demo version of the application is downloadable from oziexplorer.com. The demo version has several functions dis-enabled, the most important of which is the ability to calibrate a scanned map using more than 2 points on the map.

You'll need to spend some time fiddling with the configuration settings, all of which are more than capably explained by the Help function in OziExplorer, so nothing will be gained by my repeating them here.

Now, download a waypoint file to your computer: try dua.wpt. Then, all you need to do is go to the "Garmin" menu (or your brand of GPS) and select "Send Waypoints to GPS". Locate the .wpt file on your c: drive and you're off.

It's a bit of an effort to do all of the above just for the ability to automatically upload waypoints. Fortunately, OziExplorer is much more useful than just that, one of which is its ability to manage tracklogs.

Tracklogs

You'll notice that your GPS will map your route as you travel. These squiggly lines, called tracklogs, are stored as points in the memory of your GPS. The GPS receiver then uses some kind of software wizardry to join the dots on its display. But there's usually limited space for this data. On my very used Garmin GPS 12, there is space for 1024 points, while the newer eTrex units take 2048 points. (Woo hoo!)

Because of the limited space, this data will be overwritten (if you've set the "track" setting to "wrap" in your unit) once you've used more than the alloted space. But using an application like OziExplorer, you can save this tracklog file on your computer for later use. When you want to return to the trail in question, you can upload it into your GPS receiver in much the same way that you uploaded waypoints. You can also upload a tracklog that someone else has recorded.

Download a tracklog file to your computer: dua.plt. Go to the "Garmin" menu (or your brand of GPS) and select "Send Track to GPS". Locate the .plt file on your c: drive and that's it. The tracklog will now be displayed in your GPS.

Your GPS unit will also be recording its own tracklog. It's important that you now turn off the tracklog recording on your unit. This will avoid a confused jumble of lines appearing on the display and, more importantly, will prevent the uploaded tracklog from being overwritten. (Note that on the earlier, basic Garmin eTrex unit (the yellow one), you can't turn the tracklog setting off. On the newer eTrex units (Vista/Venture/Legend) you can turn it off but it will resume recording if you turn the unit off and on again.)

To turn off the tracklog recording on a Garmin GPS receiver:

  • Go to the map page
  • Select OPT or CFG (depending on model)
  • Select "Track Setup"
  • Select the "Record" field
  • Select "Off"

You will now have a tracklog of the Sungai Dua trail displayed on the screen of your GPS. Your current position will be marked as a dot in the middle of the display. All you now need to do is to keep following the track. You should be able to tell fairly quickly (50-100 metres) if you've started to go off the correct trail, because the position marker will start to diverge from the marked track. Because you've turned the tracklog recording off, no other lines will be displayed on the screen, and the displayed tracklog will not be in danger of being overwritten.

Fancy stuff: Mapping

OziExplorer also allows you to import a scanned map and to overlay it with GPS data that you've collected. This will allow you to bring an updated and fairly accurate map with you on your subsequent visits.

In the example at right, the red line shows the tracklog recorded by my GPS on the way in to the Kerau waterfall. The waypoints mark significant points along the trail, in this example two river crossings over Sg Rogol and Sg Kerau. You'll note that the map itself shows no indication of there being a trail.

To overlay GPS data over a scanned map:

  • Get hold of a scanned map file. Make sure you are not infringing any copyright. The demo version of oziexplorer only takes .bmp files.
  • Launch OziExplorer. Go to the file menu and select "Load and Calibrate Map File".
  • Select 2 points on the map which have known coordinates, preferably 2 points on opposite corners of the map. The registered version of the software will allow you to calibrate using up to 7 points. You can read the coordinates of the selected point from the edge of the map. An easy way to do this on your computer monitor is to hold a piece of paper so that two of its sides are parallel to a latitude and longitude marked on the edges of the map. The corner of the piece of paper will be point 1. Of course, if the map has lat/long gridlines, all you need to do is to click on an intersection of two lines.

Created: 12 August 2002, Joe Adnan

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