Exercise 3

How TracBack can save you

In this Exercise we will see what can happen if you do not plan your trip and you think that you will not need a map. We wanted to do the walk, as indicated on the map extract below. From previous car trips in the region we knew that there was a small parking place besides the road at the big red arrow. This seemed so easy, that we did not create waypoints and a route for this walk.

Map extract copyright © National Geographic Institute at www.ngi.be

We marked a waypoint in our GPS76 where we left the car. This goes even without thinking. Already after 100m we had to make a choice. There was a small, not frequently used track to the left and a bigger one, uphill to the right. We did not remember that on the map (at home) we had seen 2 tracks, so the bigger one should be the one on the map and the one we wanted to walk. At this point we did not even mark a waypoint. After 220m we looked back and saw the landscape and the track as in Photo 1. Here we took a photo and marked waypoint 002. We repeated this at the points 003 and 004 (photos not shown). See the graph under "Analyzing the trip" near the end of this page for waypoint locations.

Photo 1

At 005 we marked a waypoint, because it was clear that we no longer were on a track. See Photo 2. The weather was good and the soil not too muddy, so we went on. We remembered that somewhere our walk had a sharp turn to the right and as we now were in the middle of agricultural land without track, nor trail, we decided to turn 90 degrees to the right. Now we marked a waypoint for navigational reasons. Maybe we had to come back through this point.

Photo 2

So we went over the hill and descended and of course, in reality we arrived at the trail below, but for this Exercise we will suppose that from this point, there is no way to continue and we have to do a TracBack. We came from over the hill in Photo 3 and marked waypoint 007.

Photo 3

As we marked waypoints along our walk, we could create a route from point 007 to point 001 and navigate that route, as done in Exercise 2. But here we will not use our waypoints, but instead execute a TracBack.

TracBack Navigation

Most receivers will not let you navigate the Track Log, so before we can do a Track Navigation we have to save the track. With the GPS76 it goes like this: "Main Menu", selection "Tracks", "Enter". "Save" will be selected. Press "Enter" and the track log will be saved with the actual date as name. Change the name if you prefer something else. Select the saved track and press "Enter" again. On the next screen select "TracBack" and press "Enter". A small pop-up menu lets you select "Direction to Navigate": "Original" or "Reverse". Choose "Reverse" and press "Enter". This brings you to the Satellite Page. Press "Page" to go to the Map Page. Here you will see that your GPS receiver has drawn a route, that rather well represents the traveled track. In our case it only uses 3 Route Legs and 4 Points. The start and end point, a point that coincides with our point 006 and a fourth point, that is not one of our waypoints (between 001 and 002).

The next picture shows the route, as calculated by our GPS receiver.

For the "photo" we wanted the whole route to be visible, so we had to zoom out and pan the map. That is the reason why the Map Pointer is visible. Near waypoint 005 we made another screen shot of our GPS receiver. The next picture shows the result.

The arrow indicates that we walked exactly on our footprints, in reverse order. Waypoints 008 and 009 are introduced accidentally when we linked the GPS76 to the laptop, laying the GPS receiver with its front-side (buttons) on the laptop when entering the cable at the backside of the receiver. Fieldwork is not always easy. They have no significance and we deleted them from the waypoint-list afterwards.

The actual Track Log

The next picture shows the Track Log, as it was recorded during our walk.

Map extract copyright © National Geographic Institute at www.ngi.be

It is obvious from this projection that in the beginning of our walk, we should have taken the smaller track to the left. If we would have entered some waypoints for this walk into our GPS receiver, before leaving home, we would not have made this mistake. And if we had brought a paper map with us, this would have been avoided too.

Why not just walk back and try to follow the Track Log line on the Map page?

First of all the Track Log line is a very thin line on the Map page. When it rains or snows on your GPS receiver, you will have trouble to see this line. The TracBack line is much thicker, consists of straight line segments and is much better visible.

More important yet is the fact that your GPS receiver calculates a route with Turn points when you ask a TracBack. In case that your GPS receiver has an audible alarm, it will warn you when you approach these points. The TracBack navigates you from one Turn point to the other and knows where you want to go, not only where you go. This way it can much better inform you about Bearing, Track, Off Course, etc. In other words it guides you. You do not have to find it all out yourself.

The most important is maybe the fact that, as TracBack is a navigation mode, you can also use the Pointer page or the Highway page, which could be more convenient in certain circumstances.

If you don’t ask your buddy to help you, he will leave you alone, but in situations, where you (have to) decide to go home, the way you came, a little help might be welcome.

Analyzing the trip

Now we will analyze our adventure with GARtrip , a wonderful shareware program. We downloaded the track log and the waypoints into the program and with a little playing we obtained the picture below.

The line graph is clearly our track and the diagram below represents Altitude versus Traveled Distance with indication of speed in the form of different colors. The larger red zones right of the 1,0 and 1,5 km markers represent the moments where we manipulated the GPS receiver and the laptop in order to make the 2 screen-shots. Our average speed had dropped below 2 km/h (user defined), represented by the color red (user defined). The track speed was 20 sec averaged (user defined). The smaller red lines, left from the 1,0 km marker, indicate the places where we took some time for taking a picture.

Play back the Track

Using the program, you can play back the track manually or automatically and read simultaneously in the line graph and the diagram, which point you are looking at. At waypoint 002 we did some steps back for photo-composition reasons. On the play-back one can clearly observe these steps. There are so many variables, that can be changed, that one always finds the right amount of detail in the presented graph and diagram. This tool lets you remember everything that happened during your trip.

Remark about TracBack

This technique is very useful in town, where you want to find back your car or your hotel. In town you normally make much more sharp turns than in the country-side, so the TracBack route will show you exactly the streets where you came through. Here is a simple example.

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