Lab 7: Field Navigation Using a GPS Unit



Introduction:

In the previous field navigation exercise, a simple field map and compass was used to successfully find particular locations at the Priory in Eau Claire, WI. While effective in identifying the hidden points, there were some issues that made navigation somewhat difficult. Chief among them was the process of step counting, and maintaining a perfectly straight bearing. The terrain and weather conditions were the main reason for these problems. Our step count values were obtained by walking in a straight line, on concrete that was cleared of any obstructions, making the journey very easy. When actually conducting the field navigation exercise, our path was anything but clear. There was at least a foot of snow on the ground, making step counts extremely inaccurate. Additionally, maintaining a perfectly straight bearing was complicated by the abundance of trees and shrubbery that covered the wooded area surrounding the Priory. Technology has allowed for some of these inconveniences to be remedied, and a contributing factor to that is the advent of portable GPS units. For this field navigation exercise, instead of using a map and compass, a Garmin E-Trex, shown in Figure 1, was used to navigate from point to point.

Figure 1: A Garmin E-Trex, the GPS unit used in this exercise
http://www.newsroute.info/TechReviews/GarminEtrexLegend.html

Methodology

Once arriving at the Priory, each person was given an E-Trex and a set of UTM coordinates. The GPS unit had to be calibrated to read your position in UTM, and once this was done, navigation could occur. To do this, the UTM coordinates provided to all the groups on the chart needed to match the coordinates on the GPS unit itself. Northing and easting directions were given, and to get where you needed to. If the northing needed to be decreased from your current position to get to the navigation point, you would walk south. If it needed to be increased, you would walk north. The same goes for the easting position. If it needed to be decreased, you would walk west. If it needed to be increased, you would walk east. By using these values, the group was able to efficiently navigate from point to point successfully. As with the previous navigation exercise, each point had a tool that you could punch you card, recording your successful finding of that respective area.
After completing navigation, the tracklog of the E-Trex had to be downloaded onto a computer to then import the data into ArcMap for manipulation. A program called DNR GPS, a piece of open source GPS software, was used to transfer the data off of the unit and onto a computer, where it was later saved as a point shapefile. The shapefile was then imported into a geodatabase, where it could become a feature class, and was finally then able to be brought into ArcMap for manipulation. All of the tracklogs from the class were uploaded to a feature dataset, so that all of the data could be accessed by everybody in the class. Figure 2 shows a map of my tracklog, and its relation to the navigation points that we had to follow. The video below the map shows a time-lapse progression of the navigation from point to point. Be sure to watch the video in full-screen to accurately see everything that is represented on it. Our group had to follow the 1A-6A points, which are marked on the map and video, and illustrated in Figure 3.

Figure 2: Individual tracklog for my GPS unit.

Figure 3: Copy of table containing UTM values used to navigate to the points.

The next map that was produced was one of all of the members in my group and their routes, shown in Figure 4. While this may seem redundant, as all group members should have the same tracklog records, this is not the case. When trying to find the navigation point, often times we would split up and look in different directions if we thought we were close. This cannot be shown on individual maps, but the group map can demonstrate this.

Figure 4: Map of my group's tracklogs in relation to the navigation points we were following.

Finally, the last map created was a collection of all groups that participated in the exercise, and the routes that they took to get from point to point, illustrated in Figure 5. As you can see, the courses took groups across the entire wooded area surrounding the Priory. Additionally, the paths cross in certain places, adding one more challenge to navigation, as each group had to be absolutely certain of their position, or risk steering toward a navigation point that was not theirs to find.

Figure 5: Tracklog records for the entire class, relative to the navigation points they were trying to find

Discussion

Figure 6 : Snowfall map of the state of WI on March 11, 2013.
Retrived from NOAA

As convenient as using the GPS unit to navigate through the various courses at the Priory, the process was not without issue. The first was something that could not be controlled: the weather. On the date of the field exercise, March 11, 2013, the Eau Claire area was hit with a fairly substantial amount of snow. Figure 6 shows a precipitation map of the state of Wisconsin on that day, with Eau Claire County getting almost eight inches of snow.  This made getting to the Priory difficult if proper precautions and planning were not done. Unfortunately, the group that I received a ride to the location did not take this into account, with a vehicle of a classmate being unable to drive in the snow. Thinking quickly, we used my car to get a number of people to the site. Unfortunately, at this time, we were already late for the activity, and the groups had left without us. After being given our GPS units, those who had been late were instructed to find their groups. For me, this was easier said than done. I attempted to find my group, but with no luck. The GPS unit was unfamiliar to me, and while I had an idea how to use it, trying to find the point where my group left was personally difficult for me. At one point, I managed to find another group, and I joined up and completed the exercise with them. I realize that this was not following the directions, and am disappointed in my perceived confidence with the E-Trex, which led me to having to abandon my group and join another one, just to avoid getting lost in the woods trying to find the navigation points on my own, while trying to look for my group members.
Another issue that was encountered was the accuracy of the GPS unit. Because of the heavy tree cover, sometimes getting a reading was difficult, because the E-Trex would pause while looking for a strong enough signal to give accurate coordinates. This was not an issue with the field map and compass navigation exercise, as the only thing that would prohibit our understanding of the map was our eyes. If we produced an accurate map, and had plotted direction and bearing values accurately, proper navigation was almost guaranteed. By using GPS units to navigate, we were at the whim of technology. If the tree cover was too thick, the E-Trex would not have a signal, and would render navigation impossible. Also, the GPS unit relied on batteries, which die after extended use. If the GPS unit ran out of power, it became just a rectangle in your hand that you can do nothing with. These pros and cons of using both a map and compass, and a GPS unit, need to be balanced with each other, and, using this balance and understanding of the limitations of each method, an appropriate tool can be selected to tailor the kind of navigation that is required.

Conclusion:

This field navigation activity demonstrated the benefits and drawbacks of using GPS units in attempting to successfully navigate a terrain. The technology that the Garmin E-Trex can offer in assisting the user in locate their position and move them from place to place is a significant improvement in using a map and compass to do a similar task. However, as technology often fails, the GPS units are susceptible to mechanical issues, like any other piece of equipment. Batteries can die, rendering the GPS itself useless. Tree cover can block a signal, affecting the accuracy of the plotted position. And operator error in reading the coordinates and understanding the unit can also prevent successful navigation. But even after considering all of these possible avenues for error, the GPS units do make the job of tracking and orienting oneself much easier than using a map and compass. While maps and compasses do not run out of batteries, or have their signal blocked from high levels of tree cover, they cannot tell you how far off course you are, or orient you in the right direction if a wrong turn is taken. At the end of the day, each method has its own benefits and drawbacks, and it is up to the person conducting field research to choose the method that will be of most use to them, and the one that will give them the most accurate results.