Lab 7: GPS Land Navigation

For this week’s lab, our task was to again navigate the Priory using UTM coordinates to locate each waypoint. Instead of using the traditional methods employed in the previous session (pace count and azimuth), only handheld Garmin E-trex GPS units would be used. Although the Garmin units are relatively inexpensive and only contain basic functions, they still operate on with a reasonably high level of accuracy allowing for their use in navigational exercises.

Fig. 1: Shown above is an example of the GPS unit used to navigate the Priory 

There are multiple ways of preloading the waypoint coordinates into the GPS unit to aid in navigation, but that was not allowed for this exercise. The only function allowed on the GPS was the real-time display of the GPS unit’s current position shown in UTM NAD 83 Zone 15 N coordinates. Each team was to then wander around to find the specific waypoints based solely on their ability to reference the coordinates displayed on the GPS unit to aid in their movement to the coordinates of the predefined waypoints.

To show each teams efficiency in finding the waypoints on each course, the tracklog function on each GPS was turned on. By turning the tracklog on, points were plotted at a predetermined interval, usually every 30 seconds, to show where each group traveled by creating a digital trail of breadcrumbs. These tracklogs would then be uploaded from the GPS units and loaded into a session of ArcMap with the location of the waypoints overlaid upon them to see how accurately navigation could be done using only a GPS.

Although it took a little while to orient ourselves using nothing but the GPS for navigation, it did not take long for our group to begin to travel in the correct direction to our first waypoint. Since we had three team members, we decided to use each member for a specific task. One team member took control of finding the X segment of the UTM coordinate, another team member moved in the direction of the Y portion of the UTM coordinate, and the third team member directed the pair to move in unison by combining their respective directions of travel to find the correct bearing to the waypoint.

Fig. 2: Shown above is the tracklog uploaded from the GPS unit displaying movement from point to point on course three at the Priory.

Fig. 3: An overlay of each team members tracklog on course three at the Priory

As seen in the map of displaying our team’s tracklogs, navigation utilizing only a handheld GPS unit is possible, but requires quite a bit of energy to do so. It is clear on the tracklog maps that travel from point to point was not as the crow flies. Quite a bit of “zig- zagging” can be seen in the tracklogs because it was sometimes hard to establish a direction of travel with the X and Y coordinates both convening on the waypoint in unison. Generally, we would overshoot one portion of the coordinate and have to create a right angle from our current position to move laterally to the correct location of the waypoint.

I found this lab interesting and very useful because it provided a perfect example of how useful GPS technology and the UTM coordinate system are. By having us walk around following the UTM coordinates displayed on the GPS, it showed how they are simply broken down into meter increments that are northing and easting from the origin of Zone 15 N. Essentially we were just traversing a massive X, Y coordinate plain and once that concept was understood, navigation from point to point was simple and straightforward.

Fig. 4: All class members tracklogs displayed according to the course navigated at the Priory.