Azimuth & Distance Survey

Introduction

With recent modern technologies the old ways of surveying techniques have begun to go obsolete. Techniques such as the azimuth and distance(A&D) surveying method have all, all but gone extinct. Replaced by more convenient and efficient options such a global positioning systems. However, these modern technologies are not a 100% reliable and not only can they fail, but they will fail. Whether it be loss of battery power or poor weather conditions, modern technological devices will have downfalls and when it happens it is crucial to have alternative methods of completing tasks. Exploring the surveying technique of manually recording the azimuth and distance measures to record data is a good way to understand alternatives to modern technologies. 

Study Area

The study area for performing the A&D survey exercise was decided to be an open area on the University of Wisconsin- Eau Claire's campus. The UWEC campus was the ideal location due to my partner and I's familiarity with the area. The section of grass was perfect for the exercise because it allowed for vision of far away objects. Having a location that has good vision is key to conducting a good distance and azimuth survey.  

Methods

The A&D survey method consists of exactly what it sounds, measuring of both the distance and azimuth from a given spot, called a reference point. The object of the A&D process is to select a landmark or distinguishing feature(trees, poles, cars, etc) and measure its azimuth and distance relative to a selected reference point.  This reference point is key, as it is the base for all measurements recorded throughout the A&D technique. Using a good reference point can be very beneficial in the long run. Choosing a reference point that can be easily identified on a aerial photograph will allow for comparisons to be done to see how accurate the recorded data actually is. A reference point such as the corner of a known building will enable the user to find the coordinates of that position and give the data a spatial reference. 

Figure1: Aerial Image of the UWEC campus with the yellow dot representing the reference point used

Once a reference point is determined, measurements can then be taken. The most common way for this to be done is with a compass and a tape measure, or another measuring device. It is important to remember that all of the data that is collected is relative to the reference point. Therefore, it is not explicit data and should not be used as such. 

For efficiency and time concerns, my partner and I used a TruPulse Laser device that is capable of identifying the distance and azimuth via laser technology. This laser provides an extremely more accurate representation of the compass and distance if they had to be recorded manually. We also found the location of our reference point by using an app from a mobile phone that gave the coordinates. Of course since this method is generally used when technology is not working properly, the methods stated above(easily locatable reference point and compass/tape measrue) are more applicable.

Figure 2: TruPulse laser device used to record azimuth and distance

Figure 3: Excel table showing the data recorded. The Latitude and Longitude is the location of the reference point. 

With all of the data points collected, they can then be imported into ArcMap. Importing the data into ArcMap will allow for data creation within the software. The first step of importing the data, is to create a geodatabase to store everything that will be created. With a custom geodatabase created the Microsoft Excel spreadsheet can be imported. With the imported spreadsheet a tool called Bearing Distance To Line can be run, which will use the distance and azimuth fields to create line features from the reference point.

Figure 4: Path to the Bearing Distance to Line tool within the Arc Toolbox

After the Bearing Distance to Line tool is ran, the Feature Points to Vertices tool can be run. This tool converts the ends of the lines into points, thus creating a point for each landmark that data was collected upon. 

Figure 5: Path to the Feature Vertices to Points tool within the Arc Toolbox

Results

Figure 6: Results of the Bearing Distance To Line tool. Each line leaves the reference according to it's azimuth. Each line ends according to it's distance.

Figure 7: Results of running the Feature Vertices to Points tool. Each orange point represents a land mark or distinguishing feature data was collected upon.

Discussion

The results of the tools show that there appeared to be some errors with the data. The first errors that were noticed were some of the points were substantially closer to the reference point than what they should have been. After looking over the excel table again it appeared there were multiple data entry errors. This shows the importance of going over the data entry process slowly and accurately. This includes double checking, because sometimes data entry errors will not be easily apparent. 

Other errors are also apparent in the results, specifically the points that show up over buildings. Although we did collect points close to many of the buildings, they should be on the edge of the structures not in the middle. This could be perhaps due to an error in the mobile app finding the latitude and longitude coordinates of the reference point. This shows the importance of having a good reference point. My partner and I, chose not to use a reference point that is easily identifiable and instead chose one in the middle of a grass field.

The accuracy of the laser seems to be fairly good. There is only one extreme outlier that appears to be inaccurate. There is one line that is extremely far into the woods. Although this was indeed a point that was a great distance away it should not have been that far away. This could either be due to user error in handling the laser, or perhaps just an inaccuracy with its technology. Because this point was are furthest in distance, in may be a factor of both types of error. 

Conclusion

Learning the azimuth and distance surveying technique was a great exercise in understanding just how far technology has come. Despite the great benefits of technology it still can fail and it is still important to understand alternative methods of data collection when out in the field. Not only did this exercise show one technique of surveying without technology, it presented the idea of needing to be able to think outside the box if problems arise. Rarely when out in the field will everything run smoothly, so being able to think on your feet and be creative when tackling unexpected issues is a skill that every geographer should learn.