GPS Navigation

Introduction
Over the past few weeks, our Geospatial Fields Methods class has been exploring different land navigation techniques at The Priory.  First, the traditional technique of using a map and compass was used to navigate to six different point markers in a wooded area.  This week a Garmin eTrex GPS unit was used to navigate to six different points.  The GPS units had the tracking feature on, which was used to create maps and an animation showing the routes of students through the woods.  Next week we will be participating in a paintball activity that involves navigating to as many points as possible.  

Methodology
In preparation for last week's field outing, we needed to establish our pace count and create the navigation maps that we were to use out in the field.  Our pace count was established by marking off a distance of 100 meters and counting the number of paces it took us to walk it.  I found my pace count to be 65.  To create the navigation maps, data such as a orthophotograph, two-foot contour lines, five-foot contour lines, and a DEM was used.  A UTM grid was also placed over the map to aid in the navigation.  On the day of the field event, we plotted the locations of the points that our group was assigned to navigate to.  Straight lines were then drawn from point to point, and a compass was used to measure the bearing.  We then went out in the field and began our navigation event.  Our group utilized a three-person system for the exercise.  One person had the compass and would direct a person to walk to a specified location on the bearing.  The final person would then walk to that person and count the number of paces to estimate the distance traveled.    

This week, we were to use GPS units to navigate to the points rather than using the traditional land navigation techniques using a map and compass.  Each student was assigned a Garmin eTrex GPS unit for the activity.  The unit would be used to locate the navigation points that we were assigned and to track the routes that were taken while navigating to the points.  My group was assigned the points on course 3, and started at point 1B and then went to point 2B.  The other group that was assigned to course 3 started at point 1B and went to point 6B.

Table 1. Navigation Points

My group utilized the UTM coordinates to navigate to the points.  To get to the points, we generally began by navigating to the correct x value, and then walked to arrive at the correct y value.  A recent snowstorm made walking slow and a bit difficult.

Figure 1. Hannah and I examining our GPS units at a point marker.

After we navigated to all of the points, we returned to the parking lot where the class was congregating and turned off the tracking on the GPS units.  This data was then uploaded as a shapefile using the Minnesota DNR Garmin Application.  The shapefile was uploaded in the NAD 1983 UTM Zone 15N projection to be consistent with the other files that were used for mapping of the priory area.  Each student's track log was then imported into a feature dataset which allowed for access of all of the files for everyone.  This data was then used to create maps displaying the track log from my GPS unit, the track logs for my group, and a map containing the track logs of everyone in the class.

Map 1. Track log from my GPS unit.

This map shows the route that I took during the field navigation event.  Symbology was used to display the beginning of the track in a lighter color.  The color then gradually becomes darker as the track progresses.  This data was then used to create an animation of the track.  To do so, the file was selected as a time track under the properties.  The animation toolbar was then used to create and export the video.  The video can be found here: http://www.youtube.com/watch?v=iP7FNiIi3xk.  The files from the rest of the students in the class were added into ArcMap and maps were created to show their track logs.

Map 2. Group GPS Navigation Map

This map displays the track logs for Hannah and me.  Mitch's file was not in the file when it was accessed.  As you can see, Hannah's track log had much fewer points, and is most likely due to a difference in the increments that the GPS unit took points.  

Map 3. Class track logs.

Discussion

After the completion of this field outing, it was apparent that navigation with a GPS is easier and faster than traditional navigation with a map and compass.  GPS navigation does not require any preparation time, and it is much quicker in the field because a person can continuously walk and not have to worry about walking to a certain spot on the bearing and count the number of paces.  It also can be accomplished easily by oneself, whereas in the traditional method, a three person group is ideal.  Another advantage of GPS navigation is that a waypoint can be created on the GPS and it will tell you which direction and how far to travel to this location.  We did not do this during our navigation exercise, but this would have been very helpful and effective to do.   

Even with this benefits of GPS navigation, we did run into a few minor issues in the field.  It was very easy to misread some numbers when walking and looking at the GPS which led us a little out of our way a couple times.  An example of this can be seen in the video of my track between points 3, 4, and 5.  When using UTM coordinates, it is important to remember that the x values increase as you move to the east, and y values increase as you move to the north.  A map accompanying the GPS unit can be very helpful to visualize this when determining the direction to travel.  Finally, GPS technology can not always be relied upon so it is important to have an understanding of traditional navigation techniques.  The batteries in the unit could die, or you could be in an area where it is difficult to obtain a reliable signal.