Jonathan Keller
FRS 144
Waypoint Hunt
2/11/06
Introduction
In this exercise, Andrew Goetz and myself went in search of a boulder for which we had a close-up picture and coordinates. The information we had is shown below in Figure 1. Using our Garmin Etrex Legends, Andrew and I navigated from Blair Arch to the location of the boulder, a few hundred feet due south of Jadwin Gym. We traveled a distance of nearly a mile and then took data to see the accuracy of our receivers.
Figure 1
Method and Route
For the first part of the hunt, Andrew and I relied on his receiver while mine was still locating satellites and targeting our exact position. Our accuracy ranged from 7-20M throughout the expedition. Our best signal was reached when out in the open and not near any buildings, for example when we were very close to the boulder itself we were in the open and had a good accuracy. Our worst signal/accuracy reading was obtained while walking alongside the large Jadwin Gym complex, where we had weak signal from four satellites. A picture of our complete route is shown in Figure 2 (path in red for all maps).
As can be seen from the route map, we started by heading SSE from Blair Arch, until about a quarter of a mile (402 meters) later we reached the Whitman College construction site, where we were forced to head almost due east for a couple hundred meters. Noting our location and guessing at the location of the boulder, we headed due south for a hundred meters until we reached a major pedestrian road heading east. We then traveled east on this road for about a third of a mile (536 meters) until we reached Palmer Stadium. We tried to keep our distance from the stadium as to avoid losing signal from the satellites. Andrew and I then headed SSE again in the direction of Jadwin Gym. Since we thought the boulder was still a bit east we bore east across the northern side of Jadwin Gym. We were afraid of losing signal by going between Jadwin and the swimming complex so we continued, too far east, around the swimming complex. After curving around, we took a relatively straight SW path in the direction of the boulder. A close-up picture of the end of our route is shown in Figures 3 and 4.
Figure 2
Figure 3
Figure 4
Due to the inaccuracy in the hundred-thousandths place of the boulder’s coordinates, it took Andrew and I a little bit of searching before we found the boulder. Figure 5 shows a picture of me with the boulder.
Figure 5
Data
GPS Receiver / Latitude / LongitudeGiven Coordinates / 40.34233 / -74.64770
Jon’s GPS Coordinates / 40.34230 / -74.64780
Andrew’s GPS Coordinates / 40.34226 / -74.64773
Analysis
The data seems to be very close for all coordinates. All of the coordinates are within significant figures (1 ten-thousandth of a degree). Andrew’s coordinate for latitude is the furthest away from the given coordinates with a difference of 7x10^-5 degrees. My longitudinal coordinate is the furthest off of all readings at 1x10^-4 degrees different. The percent error for the readings is:
Jon’s Latitude
(40.34233-40.34230)/40.34233=7.4x10^-7 x100%=(7.4x10^-5)%
Jon’s Longitude
(-74.64770+74.64780)/-74.64770=1.34x10^-6 x 100%=(1.34x10^-4)%
Andrew’s Latitude
(40.34233-40.34226)/40.34233=8.18x10^-6 x 100%= (8.18x10^-4)%
Andrew’s Longitude
(-74.64770+74.64773)/-74.64770=8.0x10^-7x100%=(8.0x10^-5)%
Thus the data was very similar and within the 7M of accuracy that the GPS receiver registered when we were by the boulder.
Conclusion
The GPS receivers are as accurate as they say they are based on the very, very low percentage error in the experiment. If the receivers had not been accurate we most likely would not have found the boulder in the first place. The exercise was successful in teaching us how to use our GPS and to test their accuracy.