Exercise 9: Topcon Land Survey

Introduction

The purpose of this exercise is to familiarize ourselves with the Topcon Total Survey Station. The TSS is a very precise piece of surveying equipment capable of reproducing landscapes in digital format. Common uses for this type of surveying equipment includes: road construction, land surveying, and law enforcement mapping. The TSS will be used to capture the landscape within the green space at UWEC. Once the points have been collected using the TSS and the GMS-2 GPS unit, they will be imported into ArcMap and interpolated to show elevation change within the UWEC green space. 

Methods

The study area for this exercise is the green space north of the Davies Center at UWEC. This area offers a wide open space for data collection as well as elevation changes for the Little Niagara stream that passes through it. 

Figure 1. The perspective of the TSS at the study area. Notable features include a elevation decline from right to left with the Little Niagara Stream just out of sight on the far left side. 

The first step to operating the TSS is correctly setting the unit in place. The three legs must be planted into the ground and then calibrated using the various turn knobs located on the legs. With the legs secure, the water level on the unit can be used to fine tune the balance of the unit. Each of the three ends of the platform must be adjusted so that the level shows it is balanced. With the legs and platform ready, the TSS unit can then be placed on the platform and secured using a screw on the platform. After turning the unit on, it is essential to connect the GPS unit via Bluetooth. 

Before any data collection can begin, unit height, receiver height, and occupied point must be set. The unit height can be found by measuring the distance from the ground to the height line specified on the side of the unit (1.78m during our data collection). The receiver height can be found by reading the measurement on the receiver unit (2m during our data collection). In order to set the occupied point, we simply collected a point directly under the TSS using the GPS. With this point set as our occupied point, we can now begin to collect data for the environment around us. 

Our team contained four members, so we decided it would be best for one person to hold the receiver and move around the landscape, one person to use the TSS to scope onto the receiver, one person to operate the GPS device, and the final person to rotate between positions. The receiver took the raised prism and chose various locations in the green space while the TSS operator zeroed in on the exact center of the prism. Once the scope was centered on the prism, the operator would call "fire" and the GPS user would hit the collect point button. After a few seconds of data collection, the GPS unit would chime and tell us that the point was successfully collected. Once we heard this chime, we would shout to the receiver to inform them to move locations. This process was repeated until 100 points were taken in the green space.

Figure 2. The TSS operator aims the scope directly onto the receiver prism. Once in position, he tells the GPS operator to collect the point. 

Figure 3. The receiver holds the prism so that the TSS operator can aim into the center. The prism's bright orange sides make it easy to spot from a distance. 

Results

After importing the points into ArcMap, we than conducted spatial interpolation to get a better idea of the landscape of the green space. The occupied point is represented by the yellow point towards the right in both Figure 4 and Figure 5. 

Figure 4. The raw points as they were imported from the GPS unit.

Figure 5. Spatial interpolation by using the kriging method. The elevation decrease is quite obvious as well as the location of the stream in the dark green portions.

Discussion

Once the station was successfully set up, data collection was a breeze. Our group did however spend almost an hour trying to set the occupied point, which dragged the data collection on for much longer than it should have. We had a very limited time to learn how to operate the unit before data collection and the notes that were provided seemed unclear at times. 

Another problem during data collection was the Bluetooth connectivity of the GPS unit. Nearly every five minutes the unit would disconnect from the TSS and we would have to back out to the menu in order to reconnect it. This process wasted a lot of our collection time and caused us to be out in the cold for much longer than we had hoped for. 

The final issue we ran into was the data orientation. During the backsight setup, we accidentally set the back sight incorrectly by exactly 180 degrees, causing our data to be rotated 180 degrees as well. This issue was solved by locating the occupied point and rotating all the data around it.