Field Navigation Using GPS, Map & Compass

INTRODUCTION

For this exercise, navigation of the University of Wisconsin-Eau Claire's Priory and Children's Nature Center was achieved using a GPS device and coordinates and then using a UTM map and compass. The purpose was to simulate accurate navigation in challenging conditions and terrain during field work. The priory is a wooded, hilly lot owned by the UW-Eau Claire on the Southwest side of Eau Claire, Wisconsin (see Figure 1). The fieldwork was performed on November 4th, 2007 on a rainy morning.

Figure 1: The area of interest for the Field Navigation Exercise

METHODS

GPS and Coordinate Navigation

The first round of navigation used a Bad Elf GPS unit and specified coordinates to find marked trees located in the Priory. The class was split into five groups, each with separate UTM coordinates. The coordinates listed below are for Group 1:

1. 617713, 4958075

2. 617767, 4958224

3. 617640, 4958159

4. 617553, 4958074

5. 617579, 4957938

Each group track logged their path between marked trees using their Bad Elf GPS unit gathering a continuous line of data during navigation. Students then recorded coordinate locations of the marked trees in a field notebook and took pictures at each location. The photos were then geotagged to be imported into ArcMap.

UTM Map and Compass Navigation

For the second round of navigation, students used a UTM map and compass to find the previously marked points. Students also carried Bad Elfs to collect track logs of their navigation using only the compass and the UTM map but not to assist them. 

In order to navigate distance using the UTM map, students determined their pace before collecting data. Pace was determined by measuring the number of strides it took an individual to cover 100 meters. 

In order to navigate direction, the compass was calibrated to find the correct bearing as shown by Figure 2. Since the compass arrow points toward magnetic north, to find true north students adjusted the bearing using the declination. 

Figure 2: The UTM navigational map of the Priory and a navigation compass

To find the bearing, a line was drawn on the UTM map connecting a point to another. Then the compass edge was placed on the drawn path while the bezel was rotated and aligned with the north UTM lines as shown by Figure 2. From there, the index line read the azimuthal direction the students needed to travel on their path. The final step is to align the red arrow on the bezel with the magnetic arrow on the compass.
The groups then had one student remain at the start and find location, picking out an object in-line with the correct direction. The next student would then walk toward the mentioned object counting the pace, keeping mental note of the distance. Once the student reached the target object, both students would reconvene at the object and repeat the process until the marked tree was located.

Processing

To transfer the GPS track logs from the Bad Elf GPS device, they were exported to an iOS device in a kml and gpx file, then emailed to each group. Next, the kml files were converted into a layer in ArcMap using the KML To Layer function. The layers were then projected to the NAD_1983_UTM_ZONE_15N (the same used in the navigation map and coordinates of the marked trees feature class provided).

The photos were then transferred using the GeoTagged Photos to Points function. Corrections in geotagged locations, Geosetter was used to edit the picture coordinates. The correct coordinates were entered into the point and saved as a kmz file from Google Earth. Once again, the KML to Layer function was used to convert a more accurate geotagged photo feature class.

RESULTS & DISCUSSION

GPS and Coordinate Navigation

Group 1 reached only four of the five points (see pictures shown below) because they ran into a hunter on the western boundary of the fifth point who claimed he knew the true boundary where he could hunt. Although the five geographic students had a UTM map with the parcel boundary, the students were hunting for much lower stakes, so they let him have his way. 

                                            

                                              

The GPS track log from Group 1 is shown in Figure 3. Even though the students were given a GPS device and a compass, there were still difficulties in immediately locating each point. As shown in the pictures above, some of the trees weren't blatantly marked depending on the angle at which the students saw the tree. Differences in topography, from hills to valleys also dictated the easiest path the students traveled. Finally, vegetation and the type of brush also factored into the path the students took due to thorns, thick brush, and wet swampy areas. Traveling with new students also had a minor effect on communication and leadership during navigation. 

Figure 3: Group 1's travel log using the Bad Elf GPS for navigation to specified coordinates

The GPS track logs from all groups in the GEOG 336 class is shown below in Figure 4. Mostly all of the groups hit their points, but had minor deviations from a straight-line shot between points. The same struggles listed above factored into the results of the rest of the class. 

Figure 4: UWEC GEOG 336's travel logs for specified coordinates using the Bad Elf GPS

UTM Map and Compass Navigation

During navigation using only the UTM map and compass, a predetermined pace of 61 strides per 100 meters was found for the author of this blog to determine distance. However, during navigation on a constantly-changing topography, the pace was used loosely--only an estimate at best.
Next, a declination of -2 was found for our location to determine direction. This -2 was subtracted from our bearing measurements from point to point.
However, during collection of data, an error occurred and Group 1's GPS device stopped recording the track log altogether, resulting in loss of data. Since neither student owned an iOS device, the track log (which turned out to be the wrong one) was emailed. More emphasis on attention to the device should have been placed and better communication between group members would have remedied the situation in the field and new data could have been collected.
Also taking better note of which device was used and the confusion of deciphering which device held the desired track log could have been avoided. For future reference, if confusion or difficulties in transferring data arise, careful notes should be taken and data transferring should begin as soon as possible.
Although no data was collected, it was obvious that our path between points was not as direct as using the GPS device and coordinate information. The varying topology made counting pace for distance more difficult and cheap compasses with large bubbles made direction more challenging. Thick brush and swampy areas also presented additional challenges when trying to count pace and keep in the right direction. Most of the factors that negatively altered navigation with GPS played an even more negative role in navigation with a UTM map and compass. 

CONCLUSION

During field work, even the most careful of data collection can lead to a boundary or privacy dispute. So it was a nice lesson to weigh the cost/benefits of collecting data during a dispute and carry enough information to properly prove your right to collect. Some of the struggles in navigation are terrain, vegetation, weather, and communication. These factors can greatly dictate the actual path between points even when using a GPS unit. These factors have a greater effect in only navigating by only compass and map and should be taken into account. During data collection, special care and attention to detail should be taken while recording and even inserted into metadata if possible.