Distance/Azimuth Survey Methods

Introduction: During this activity we were introduced to a new form of surveying for us, but a old form of surveying otherwise. When we cannot access GPS satellites or when our technology breaks down, and we need basic no nonsense data collection, we can use tools as simple as a tape measurer and a compass to be able to map out and delineate different objects in a study area. This form of surveying is used to determine the distance and azimuth of an object from a single collection point. We were tasked to use this method to map out an area of interest in our groups of two and to collect information on at least 100 objects.

Study Area: Our group decided to choose UW-Eau Claire's campus mall (Figure 1 and 2) and we focused in on two different control points within the mall. The first location I would describe as the middle of the campus amphitheater (Figure 2) while the other location was the south end of the rotunda between Schofield Hall and Centennial Hall (Figure 2) We thought these locations to be pertinent to our study since we could record various items on campus (blocks, light poles, signs, and trees) and overlay them on a old aerial of campus from when the mall was still being constructed. Our study was conducted on September 30th.

Figure 1: UW-Eau Claire's location in the City of Eau Claire

Figure 2: UW-Eau Claire's campus mall and the location of the two Control Points

Methods: To do this survey we had to propagate some various equipment. The first and foremost was the TruPulse 200 laser distance finder. This thing is basically a glorified rangefinder but has very accurate readings for distance (meters) and azimuth (degrees). Using this and an notebook we were able to shoot various objects and record their information along with a description of the actual object so we could map it later. Instead of writing down block or light pole every single time we shot an object, we just abbreviated it on the notebook (Figure 3).

Figure 3: Our table we created in our notebook to log all of the data

Now that we recorded all the information we transferred all the data into an Microsoft Excel spreadsheet so we could prepare it for importation into ArcMap. One additional bit of information that we needed to collect was the coordinates of our control points within the mall. Since this data is implicit, we did not record the exact GPS coordinate of every object, but rather just the coordinate of one control point so that we could see the relative location of all the other objects compared to the control point. Like I explained earlier, this is suppose to resemble what would need to happen, in the event of a loss of GPS when you needed to collect some points for further referencing. Explicit data would be the collection of all these objects with an exact coordinate, but we ain't got time for that! Anyways, to collect the location of our control points we simply went to google earth and found the exact crack in the rock that we stood on for each point and record that GPS coordinate in decimal degrees.

Now that we had a complete spreadsheet, we imported the table into ArcMap and began the Bearing Distance to Line tool. This tool takes our controls points and creates multiple lines from those control points to the locations of our objects as described by our distance and azimuth readings. This tool proved to be quite troublesome and some troubleshooting was required. One of the changes that I needed to make was saving the Excel file as a Tab Delimited txt file. The tool did not like the was the table was read in a regular excel format so changing it to a txt file made it possible. Once I did this, I was able to run the tool and got a file that looked something like Figure 4.

Figure 4: Map showing the result of the Bearing Distance to Line tool

 Once I glanced at the data, I could tell that all the lines were in somewhat appropriate positions relative to the control points. Now I needed to add the aerial basemap so I could provide further context to my data. I used imagery from the City of Eau Claire for this activity and ended up using specifically the three inch 2709_29NW raster file. This proved to be even more troublesome as the coordinate systems could never get matched up and my data would either be in Nebraska or Minnesota. I mean Minnesota?? What an insult to my distance/azimuth data! So to mediate this, I went through a series of reprojects until I finally got to the projection that worked for both my data and my imagery. The projection was WGS 84 for the actual distance to line layer. However, I am still a little puzzled because the coordinate system for the data frame is NAD_1983_HARN_WISCRS_ EauClaire_County_Feet. The layer lines up just fine with the imagery but they are both in separate coordinate systems. This issue is not as pressing as it may seem because all I am doing is providing a relative location of these objects. If the situation was different and I needed the exact location of a pipe underground, this method would not work. For that project you would need to use a total station that has survey grade GPS on it that can accurately shoot these objects to within centimeter accuracy. For the sake of this activity though, what we did is good enough and is still considered cost effective through my eyes.

Now that I have everything lined up, I started a second tool. This tool is used to create an output feature class that resembles all my objects as points instead of lines. This tool is called features vertices to points. To run this tool I simply added my bearing distance to line layer as the input and then under one of the parameters, I selected END so that it created a point for each line at the end of the line. This tool worked like a charm with no problems what so ever and the output looked something like Figure 5.

Figure 5: Map showing the result of the Features Vertices to Point tool

Results/Discussion:
Now that I have my final maps (Figure 6) we can see how accurate this method of surveying really is when compared to how cost effective the project was. The actual points on the map where the objects are located are not the most accurate but like I said before, its good enough for what its for. Yes, we could have taken the total station out there and shot all the trees and blocks. However, imagine this,what if I got hired by a company to make a map of where all the Black Walnut trees are on their property so that they can log them off. I get out to the job site and realize that my GPS doesn't work because it cannot get enough signal, so now what? One option is to go back to the company and say that I need a Total Station and they have to fork over the thousands of dollars its going to cost to purchase it or I could survey those trees using the distance and azimuth method since the logger is not going to need centimeter accuracy anyway. All they want to know is where the relative location of these trees are and if I told them that they needed to go buy a Total Station so I could do that, they would go find themselves another Geographer.

Figure 6: Final Product Map showing the objects and the bearing from our control points.

Conclusion:
Throughout this assignment I ran into small issues such as the coordinate systems not lining up or the class as a whole having problems with the final lines because the declination was off. These issues can be solved though by different troubleshooting methods and knowledge of geospatial technology and the thinking that goes behind it. Part of the lessons I was suppose to learn from this activity is that not only do you not always need the absolute best of the best survey equipment, but in many scenarios you may not have a choice and your going to have to go old school and figure how to still accomplish the task at hand.

Metadata:
Created by Nik Anderson
Created at UW-Eau Claire Geography and Anthropology Department
Created for Geospatial Fields Methods
Created on October 2nd 2015
Created with ESRI ArcMap and Microsoft Excel