The point of this activity was to learn how to use alternative methods to survey an area. Our professor emphasizes how important it is to know how to use several different surveying methods, in case high quality technology isn't at our disposal. Without high powered GPS units, a good way to survey an area is to locate a point of origin and record distance and azimuth data to survey the surrounding area. Using this method, only one GPS point is needed (or in this case, a good aerial map). It is important to understand the process first. The azimuth is a measure of the angle that you are facing (north, east, south and west). This measurement can be affected by magnetic declination, which is the difference between magnetic north and true north. As a subject's location gets farther from the line where true north is constant, declination increases. To make up for this, degrees must be added or subtracted from the azimuth, depending on how much declination there is, and whether it is positive or negative. Luckily here in Eau Claire, the magnetic declination is merely 0 degrees 58 minutes West, which is too minimal to account for in our survey.
Methods
This was a fairly straight forward activity. All that was required was either a sonic range finder and a compass, or a laser range finder that also calculates azimuth. During the class, we each familiarized ourselves with the new gear, as we haven't used it before. To test everything out, we simply went behind Phillips Hall and recorded data using a distinctive tree as an origin point. Using the laser range finder, I recorded the distance and azimuth of two art structures, an emergency phone, and several trees. Once everyone had done the same, we entered the data into ArcGIS by creating an Excel spreadsheet and used the Bearing Distance to Line tool to create a feature from the recorded data. Before this, however, it was necessary to locate the origin tree and find out the latitude and longitude values of its position by using an aerial map. The completed feature was quite accurate, with only minor variance from accidentally moving (inconsistent origin).
Now that we had familiarized ourselves with the gear and the computer lab work, it was time to conduct our own survey on the UW-EC campus. Laurel and I decided to survey the stone benches on the new campus mall. First, I checked the aerial map to look for suitable locations to use as an origin point. We chose to use the library entrance as the origin because it is a slightly elevated platform and would have a good view of most of the campus mall. Midway through the survey, we had to select a second origin because some of the benches weren't in view. For this second origin point, we chose the doorway to Schofield Hall. We had to make sure we would be able to find it in an aerial map, and the doorway was perfect.
Laurel and I had a good process to record the azimuth and distance data. I used the laser range finder to calculate the distance and azimuth while she recorded the data in a notepad, collecting 41 points total. The field work was surprisingly quick with the laser range finder. After the data was collected, Laurel made an Excel spreadsheet of the data, which was then entered into ArcGIS like we previously did. Then, using the Bearing Distance to Line tool, we once again created features of the data. We had to make special note of which points were collected at which origin, since we had more than one.
Results
Once again, the data was surprisingly accurate. Figure 1 displays our work. There does appear to be a lot of open space between the two origins, which could be from slightly skewed data or missed benches completely (it had just snowed before we took the survey).
 |
| Figure 1: The red lines display the data collected from the library entrance and the blue lines display the data collected from the Schofield Hall doorway. Unfortunately there is no aerial photo to compare the results to. |
Discussion
I thought that the survey went quite well, and it was a quick and easy process as well. This activity was quite fun and I think that the methods we learned will come in useful later in my career. It would have been nice to be able to check our results and see how accurate our survey was, but our campus was too new to have a recent aerial photo. All in all the entire activity went well.
No comments:
Post a Comment