Lab 8: Distance/ Azimuth Survey Methods

Introduction

This week, our professor explained to the class how there can often be technical issues that occur in the field that prevent one from using a GPS. Subsequently, it is a good idea to know how to use an alternate way to accurately measure points. This other way uses angles and distance to calculate the location of points.  The purpose of this week's lab was to create a map using the distance-azimuth sampling technique.

Azimuth and distance were the major categories of information that needed to be gathered for this lab using the Tru Pulse laser (see figure 1). The azimuth, also known as bearing, is collected between 0 and 360 degrees, just like on a compass. Distance, for this lab, was collected in meters.

Figure 1. TruPulse laser which has the ability to read distance in meters and azimuth.

The survey area chosen for this lab for this particular group was the parking lot on the south side of Davies Student Center on the University of Wisconsin- Eau Claire Campus (see figure 2). This particular area was chosen based on its large number of potential data collection points. In addition, it contains a clear perimeter boundary as well as a distinctive area in which cars should be parked. This would then allow for analysis of the results to be derived from where the points of the cars were survey and the general area in which the car points should have been.

Figure 2. This image displays the panoramic view where the survey station was located.

Methods

The class split up in groups of two. Each group was allowed to use the laser as well as a tripod to remain steady throughout the surveying process (see figure 3). The survey data was collected by hand because the purpose of this lab was to minimize the potential amount of electronic based errors. A variety of fields were surveyed including survey point number, distance, azimuth, type of car, and color of car. X and Y fields were included to later be inputted into Excel to display latitude and longitude of the survey station.

Figure 3. Galen diligently 'firing' the TruPulse laser at cars in the parking lot to calculate distance and azimuth.

Once collecting 92 points, the group ran out of time and survey points to collect 8 more (as was suggested by Professor Hupy). The handwritten survey results were then typed into Excel (see figure 4). A vital piece to using this method is knowing the geographic coordinates in which the survey station is set up. Without this, the points taken are obsolete because there is no spatial connection to their location on Earth. The first time the group attempted to use geographic coordinates, the latitude and longitude were inputted backwards. This gave the group much confusion until taking a step back and looking at the pieces of the puzzle. Note that the x and y coordinates are the same because they were taken at the same survey station.

Figure 4. This is a partial copy of the Excel document. Note that there are six fields of information: azimuth, distance, type, color, and x and y. 

ArcMap was then used to display and interpret the results of the survey. In order to display the distance and azimuth angle together in a spatial setting the 'bearing distance to line' tool was used. This tool asked for the input table (the Excel survey file), x field (latitude), y field (longitude), distance field (distance column from Excel file), and bearing field (azimuth column from Excel file) (see figure 5). To see the visual of what this tool takes into account during its calculation, see figure 6. The output with its line features is seen below (see figure 7).

Figure 5. This is the bearing to distance line tool 

Figure 6. This is a visual display of what ArcMap computes to account for distance, azimuth (bearing), and x and y coordinates.

Figure 7. Output of the 'bearing distance to line' tool. Notice the lines are all derived from the single point in the eastern central portion of the map.

Once the 'bearing distance to line' tool was complete, the end points needed to be gathered to create a traditional looking point system without the azimuth lines. The tool used for this was called the 'feature vertices to points'. This tool asked for the input feature, which was the product of the 'bearing distance to line' tool. It then gave the option of 'point type', and 'end point' was chosen so that the point in which the laser hit the object would be shown (see figure 8). This would then give the group a display of the accuracy of the laser throughout the survey (see figure 9).

Figure 8. Feature Vertices to Points tool. This tool gave the output for the final visual as seen in the final map below.  The input feature for this tool was the output from the 'bearing distance to line' tool. The point type chosen was 'endpoint' to display the point in which the laser hit the surveyed car or light post.

Figure 9. Distance Azimuth Survey map. This shows the various types of car survey points that were collected. As the points got farther away from the survey base, the accuracy, based on the existing cars in the basemap parking lot, lessened. The long string of red points extending to the western portion of the map were intended to be the first set of double cars closest to Davies Student Center and Phillips Science Hall. 

Discussion

After the points were calculated in the 'feature vertices to points tool', the endpoints produced a different output than what we were expecting. The first 15 points taken very close to the survey base seemed accurate in relation to the location of the campus basemap cars, but there were also points found in Putnam Park outside of the parking lot as well as in regions that would be normally used by cars driving through the parking lot. This was also seen in the light posts which were displayed much closer to the southeastern portion of the parking lot than they should have been.

As had been mentioned in prior posts from other Field Method classes, the farther away the points were taken from the laser, the more inaccurate they seemed to be. However, that could have also been due to the small area of car that was visible for the laser to pick up.

If more time had permitted, it would have been interesting to take a GPS out and map the same points to see how the GPS and laser compare in accuracy.

One change that could be made in the future on the data collection is using more than one survey base to conduct the data. We chose one base because we wanted to put the laser to the test to see how accurate it was, in addition to not wanting to collect points from the same car multiple times.

Conclusion

This lab was intriguing because it reminded me that I should always have a back up plan in case my technology fails. Although this was definitely more of a hassle than simply using a GPS, it was good to learn another way of plotting points on a map.

Unlike a GPS, the laser needs to read the angles and distance from a single point (the survey base), which means that the desired survey points from a farther distance will not only be harder to 'hit' with the laser, but likely less accurate because of the room for error in both the distance and azimuth readings. Through this conclusion, the type of data needing to be collected using the distance-azimuth method should be in close proximity to the survey base.