GPS Navigation Exercise

Introduction

This week's exercise was closely related to the previous week's in that, once again, we were conducting a navigation exercise at the Priory. However, this week we employed a different, more modern technique of navigation. Instead of using a compass and map, all we had with us was a Garmin etrex GPS unit. This type of navigation has several advantages over the map and compass method. First of all, a GPS is way more compact and easy to utilize in the field than is fumbling around with a large map and compass. Secondly, it is way quicker to figure one's location on a GPS as well as finding one's way from point to point because the units are digitally displayed and are calculated in real time. With a map and compass, we had to slowly go through the methodology of figuring out azimuth and then pacing out the distance. This took a long time and got quite frustrating. Thirdly, a user can create a waypoint in the GPS of a particular point and then tell the GPS to find the fastest route to the point. This is a huge advantage over map and compass where the navigator can easily get off path. The only disadadvantage of a GPS is that it could fail in the field if the batteries are bad and then you better hope you packed a map and compass.
The Garmin etrex GPS unit is considered an older unit and can be purchased for relatively cheap. That said, it is still very capable for navigation purposes.

Fig. 1 - GPS unit used in navigation exercise.

Once familiar with the unit settings, the appropriate units should be set before navigating as well as double checking that the appropriate datum is set as well. In this case, the units were set to UTM, which are displayed in meters, which gives the navigator a higher accuracy then does decimal degree units. The datum was left alone at WGS84. In order to see how well we navigated, a track log was set up to display our actual track to each point throughout the course. The track log properties were set to "point", so that every defined time interval, a point was recorded with time and location. This is very useful for post-exercise analysis to be able to map out not only our track, but also to see the times it took to get from point to point. Each member of the group was issued their own GPS unit. It should also be mentioned that in the woods, the density of the forest can affect the positional dilution of precision (PDOP) on a GPS unit. Basically, the PDOP is the accuracy of a 3D position based on the number of satellites and their geometry. A low PDOP indicates a very accurate position. We didn't worry about this variable in this exercise, since we weren't doing any sort of measurements but it can be an important thing to be aware of when using a GPS.

Methodology

Once again, we were to retain our groups we were assigned from last week, but we would be navigating a different course. Each group had to navigate to 6 points, which locations were given to us again. This week Drew Peterson, Kory Dercks, and myself were 15 minutes late getting out to the field because the snow had trapped a certain individuals car in his driveway, hence we had to find another car to get to the field. By the time we got out to the field, the rest of the class had already started navigating. We were told to go to our respective starting points and then catch up to our groups. Drew and I caught up to my group and even though Drew wasn't originally in our group, he decided to stay with us since his group was doing the same course but backwards.

Fig. 2 - Drew Peterson, our adopted group member of the week.

Once all four of us were together, we took some time to debrief each other on how to navigate via GPS. Since we were using a UTM coordinate system, we knew that the coordinate display was showing a northing and an easting. As mentioned before in a previous post on coordinate systems, a UTM zone places the central meridian in the center of the zone and then anything east of the meridian is an easting and anything west of the meridian is a false easting to ensure positive values. Anything north of the meridian is a northing and anything south is a false northing to ensure positive values. For our purposes, all we knew we had to do was watch how the northing and easting values were changing to navigate from point to point. Since we had a sheet with all the points in UTM format, we could determine which way we had to go based on our current location. It's just a matter of knowing that the numbers will increase when moving north or east, or decrease when moving west or south and then figure out the difference from current location and the point location. We found out that it was easiest to match the northing and easting one at a time. What this means is that we would get our easting distance to match and then get the northing to match instead of trying to match both numbers at a time. This was sort of difficult to master at first but then after finding the first point, it became pretty easy.

Fig. 3 - Kent punching his card at the first point location.

 During the navigation exercise, I was playing around with the different functions of the GPS and found out that there was a way easier way to do the navigation. The user can create a waypoint with the point location coordinates and then hit the find button on the GPS interface. This prompts the unit to draw a track on the screen to the point from the current location and tells the user which direction to travel and also how many meters away it is. I don't feel like this is cheating since it is a component of the GPS and is a very effective and efficient way to navigate. We were also very comfortable following easting and northings at by that point anyways.

The navigation conditions were once again rather formiddable. It had snowed pretty heavily the night before which meant that the snow would be deeper this time. We found that in certain spots of the course, snow was knee high. This had a negative impact on the time it took us to navigate. Not only were we traversing through deep snow, but also over very hilly terrain. Most of the course was in the woods but we managed to find a nice road to walk on for different portions between point 4a and 6a. This route also took us along the holding pond of the Priory. This part of the walk smelled awful.

Fig. 4 - Me pointing to the holding pond area.

Fig. 5 - Beatriz taking a break in the snow.

Fig. 6 - Kent finding another flag.

Fig. 7 - Me checking the next point location.

After the field exercise was over with, we took our GPS units to the computer lab where we uploaded our point data into ArcMap. Once the points were in, they were overlaid on top of a high resolution aerial image of the navigation area as well with the points where the flags were located. From here, we were instructed to make 3 maps: our personal track, our group members tracks, and the entire class' tracks.

Fig. 8 - My personal track log.

Fig. 9 - Track logs for our group (1).

Fig. 10 - Track logs for all of the groups.

Discussion

This week, our group successfully navigated through a whole course! We were pretty excited about this since last week's exercise was a navigational fail. This week we felt a lot more comfortable with this style of navigation as most of us had some prior familiarity with GPS navigation. We felt that this style of navigation was way more effective than using compass and map. We were the first group to finish, I believe and within 2 hours on top of that. Just by looking at Fig. 9 above, it is clear that we never really strayed off track at any point of the course. The only hitch we really had was between point 4a and 5a but that was because the dense forest made us change our path vs. being able to navigate in a straight line through the woods. Also, we wanted to be able to follow the road as long as possible since it was easier traveling. Looking at Fig. 10, it looks that every group did a really good job of navigating through their courses as well. Nobody really went too far off track which is really encouraging to see. I think that this shows that the entire class has a good grasp on navigating with a GPS. I think that if we were able to map out our routes from our map and compass navigation exercise, the routes would be all over the place. This proves that a GPS can be a very effective and accurate way to navigate; more so than a map and compass. I wanted to make an animated map of my track log but my GPS unit failed to collect any time data for my points. I am trying to use one of my team members' track log with time data to figure out the animation which would give a really cool graphic of our route.