GPS-101 Part 3

(Driving Your GPS Unit)

As I sit here on Fraser Island starting to write this instalment, I’m reminded of a thing from last month’s article and an additional thing I should mention.  Over the past few days on Fraser, I’ve been travelling through some dense rainforest regions and wishing that I had a more sensitive GPS receiver.  Even though I have a 12‑channel unit with an external antenna, there have been a few time where I have lost GPS reception for a few minutes in the forest.  Remember, you need to be able to receive the signals from at least three satellites for your GPS unit to calculate your position.  This is not a big problem if you’re on a track, until you come to an intersection.  So to reiterate from last month, look for a high sensitivity GPS receiver.  The additional item I’ll mention is that you should always carry maps of the area in which you’re travelling.  This could be paper-based or electronic copies.

OK, so let’s start discussing the most basic and important functions of the GPS unit:

•        Position = your current location calculated by the GPS unit.  This will be expressed in Latitude and Longitude, or Coordinates.

•        Waypoints = a planned, or recorded location – i.e. a set of coordinates to which you’ve given a name.  This could be an intersection, point of interest, obstacle, etc.

•        Routes = a series of Waypoints arranged in the order in which you intend to travel.

•        Tracks = a ‘breadcrumb’ trail of un-named coordinates.

•        Inbuilt maps, tide times and other things are useful; and certainly, moving maps can negate some of the need for Waypoints and Routes.  But let’s start with the basics and I’ll discuss moving maps another time.

For the purpose of this exercise, I’m going to assume a scenario in which I frequently find myself:  planning and running a trip.  First I’ll do a reccy (reconnaissance trip) or two and then run the actual trip.  Here’s how to go about it using the basics.

First, get some maps of the area that you want to explore.  Make sure that your GPS unit is set to the same datum and coordinate system as your map.  This way, you’ll be able to make sense of the Current Position reading from the GPS with reference to your map, i.e. be able to tell where you are on the map.

Next, plan on the map where you want to reccy.  Work out the coordinates of the roads, track, intersections, and places of interest from the map and enter them as Waypoints into the GPS unit.  This can be time consuming, because most GPS units don’t have keyboards.  We’ll concentrate on Waypoints and Routes for this instalment.  Using a PC-based program to do this can make the job a lot easier.  I’ll discuss the use of Tracks and PC software next month.

The main problem that I found with just using Waypoints and Routes is that the track from waypoint to waypoint on a 4WD adventure is rarely a straight line.  Your GPS unit will give you the bearing (direction) and distance direct to your next waypoint from your current Position, but what if you’re in the situation in the diagram below:

You want to travel along Wallaby Rd, turn right into Kangaroo Rd, left into Possum Rd, and then left into Koala Rd.  Even if there are street signs, if you’re just following a Route of Waypoints on your GPS, you could miss a turn or get a turn wrong.  When you arrive at WP001, your GPS will show you a pointer toward WP002.  This will obviously be a right turn.  When you get to WP002, your GPS will point you toward WP003, which will obviously be right turn at the ‘Y’ intersection.  Wrong!

So there are a few ways to get around this:

•        Keep a list of instructions for each Waypoint on a piece of paper.

•        Highlight the intended route on a copy of the map.

•        Put instruction abbreviations in the Waypoint name (see below).

•        Put in additional Waypoints to show you the correct direction (e.g. put a WP002A where Possum Rd crosses Platypus Ck.)

•        Use Tracks (I’ll talk about his option next month)

I find that it’s best to give Waypoints meaningful names.  These usually have to be abbreviated to between 8 and 16 characters, depending on your GPS.  Just having waypoints named 001, 002, 003, etc, is pretty useless.  Some people build directions into the Waypoint names, Some examples might be:

Your GPS will allow you to put your Waypoints in a list, called a Route.  When you put your GPS into navigate mode, you can select the Route.  Then as you reach each Waypoint in order on the Route, the GPS will point you toward the next waypoint.  The other useful thing your GPS will give you is the bearing and distance to the next waypoint and an estimate of the time required to get there, based on your current speed and heading.

When you do your reccy, always mark the actual location of the Waypoints on your GPS as you go.  This way, when you run your trip you can replace your estimated Waypoints with real ones.  Generally you don’t have to spend the time naming the actual waypoints as you go.  If your estimated Waypoints are close enough, then you’ll know what each of the actual Waypoints are and you can name them later.  If you mark additional Waypoints on your GPS, it might be useful to write down what they are; otherwise you’ll struggle to work it out later.  I run a PDA in parallel to my GPS, and use the voice recording feature to record the details.  Just push the record button and say something like, “Waypoint 001.  Go through gate in boundary fence and turn left.”  Using the record function on your PDA is also really great to record other notes about the reccy or the trip – especially if you’re doing the written, verbal, or fines for the trip.

After the reccy, use the knowledge gathered to plan your actual trip.  This time you’ll have actual Waypoints to play from your GPS.  Most GPS’s will also record the date and time you recorded each Waypoint.  This will help plan travelling times for the actual trip.

Next month - Tracks and GPS PC software. 

Happy navigating.

Greg Conlon

Last Modified on Monday, 14 July 2008
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