Lab 3: Conducting a Distance Azimuth Survey.

Introduction

In this lab we were given an introduction on how to conduct a survey of spatial points using distance and azimuth measurements from a fixed focal position. This method of gathering data can be very handy considering that you will not always be able to rely on accurate GPS technology if you either cannot find satellite coverage, if your study area is obstructed by overhead debris such as tree canopies, or if you do not have access to a GPS unit. To conduct a distance azimuth survey all you need is a compass and a range finder, and using ArcGIS tools it is possible to construct an array of points more accurate than many standard GPS units. To get an introduction to the process before conducting our own surveys, our professor gave us a quick tutorial outside Phillips Science Hall using the TruLazer rangefinder that had an integrated compass.

Methods

For our study area, me and my group partner chose Carson Park, specifically on the crest of a hill behind the baseball area and next to the playground equipment. This vantage point gave us plenty of features to record and we had just enough space between several trees overhead to get a GPS signal for our X,Y point in the form of Latitude (Y) and Longitude (X) on our Garmin Etrex.

Figure 1: Study area in Carson Park for conducting the distance azimuth survey

Once we had our work station set up and a focal point chosen I began listing off the object name, distance, and bearing for each feature we chose and my lab partner Josie would record them onto a printed off excel document. We recorded information for features such as trees (small, medium, and large), cars, signs, buildings, benches, light posts, and other park utilities. After we had reached 100 features we transcribed the data into an excel file for use in ArcGIS.

Figure 2: Excel table after having feature data transcribed

To use the excel file data first we constructed a file geodatabase and imported the excel spreadsheet into it. Then we ran the tool "bearing distance to line" which utilized our distance and azimuth fields to create lines of data radiating from our focal point to where the features lied. We then added a basemap for comparing our recorded data to the real life surroundings and based on the location of our point data the surveying techniques had been accurate and a success.

Figure 3: Line data of our features radiating from our focal point

Then we converted our line data to points using the "feature vertices to points" tool, which gave us the final product we were aiming for.

Figure 4: Point data for our features

Afterwards I symbolized the feature points by their object id to help show the distribution of specific feature types in relation to the basemap. Many of the points were trees, benches, and signs, but we also had a few singular points such as the baseball related buildings.

Figure 5: Carson park feature points

Discussion

By looking at the point data in relation to our basemap it is evident to see that although most of out features line up with where they belong, some are outliers likely caused by error in measurement when using the distance finder. The further out the feature was and the smaller the outline the more likely I was to miss the actual object and detect the distance to something behind the object. 

Conclusion

By the end of the lab it was easy to see how useful a skill using the distance azimuth method for surveying could be considering how little technology it utilizes, but yet it was evident that the method had several limitations and time consuming constraint (such as the TruLazer's inability to operate correctly in areas with electromagnetic interference). Our generated points were very close to their real life counterparts when looking at our basemap despite some user error with the equipment.