INTRODUCTION
For field exercise nine a partner and myself were tasked with carrying out two topographic surveys of UW-Eau Claire's campus mall. The first topographic survey was measured and recorded using a Topcon HiperSR GPS unit and a Topcon Tesla unit, and the second topographic survey was measured and recorded using a prism pole, Topcon Total Station, and Topcon Tesla unit. The purpose of this field exercise was to create elevation maps of the UW-Eau Claire campus mall, and get students familiar and comfortable using modern surveying equipment.
There were three reasons why my partner and I were required to conduct two different topographic surveys of UW-Eau Claire's campus mall. The first reason as discussed in previous blog posts is to always come prepared with a back up plan in case of equipment failure in the field. One piece of equipment or method may not work for every surveying scenario so it is a good idea to come prepared with back ups. The second reason for conducting two surveys of the same area of interest (AOI) is that after both surveys are conducted my partner and I could compare the two sets of data to see which method ended up working better than the other. The third reason for conducting two different surveys is that a lot of firms have budget constraints and aren't able to afford the newest surveying technologies. If this is the case it is important to be able to use older equipment and methods to get the job done.
STUDY AREA
The study area for field exercise nine was the UW-Eau Claire campus mall. Surrounded by Phillips hall in the southeast, the Davies Center to the south, McIntyre Library to the west, and Schofield Hall to the north, the campus mall is located in the center of UW-Eau Claire's lower campus. The UW-Eau Claire campus mall's position can be viewed relative to the surrounding academic buildings below in figure one.
Figure 1: shows the campus mall which is outlined in red. Both topographic surveys are to be conducted on the campus mall for field exercise nine |
METHODS
The first thing I'll run through in the methods section is the four different pieces of surveying equipment used: the Topcon HiperSR GPS unit, the Topcon Total Station, the Topcon Tesla unit, and the prism pole. I will also discuss how my partner and I utilized each piece of equipment.
The Topcon HiperSR
The Topcon HiperSR unit works in conjunction with the Topcon Tesla unit to measure and record elevation data. both pieces of equipment connect to each other via a mifi unit which allows them to communicate. The HiperSR unit is mounted on top of a tripod of known height so that the unit can accurately record elevation data, and the Tesla unit is mounted on the side of the tripod so that the surveyor can record data points at the touch of a button. The way this unit works is that it is physically moved around by the surveyor to each point he/she wants recorded. The unit is then leveled using a bubble level built in to the tripod to make sure that the Topcon HiperSR unit is directly above the desired point. Once the tripod is made level the surveyor elects for the unit to record a point using the Topcon Tesla interface. A Topcon HiperSR unit attached to a tripod is pictured in figure two below.In order to begin recording data points with the HiperSR and Tesla units my partner and I first had to create a new job (geog336_toposurvey_group3). The unit then asks for a coordinate system to project the data in. My partner decided to project using the UTM 15 North projection. We then created a point feature to use for when we actually start recording data points. After setting up our job, projection, and feature class it was simply a matter of setting up the tripod and recording the points using the Tesla interface. My partner and I set our point collection interval at five points. This meant that for every data point we collected the HiperSR unit took five points and averaged them for increased accuracy. My partner and I were supposed to take a total of 100 points to effectively cover the entirety of the AOI, but due to rain we were only able to collect 90 points. This did not greatly effect the integrity of our data, however, because we still were able to collect data points throughout the entire campus mall.
The Topcon Total Station
Like the Topcon HiperSR the Topcon Total Station worked in conjunction with the Tesla unit to measure and record elevation data. The Total Station and Tesla unit also connected via mifi in order to communicate with each other as well. The difference between the HiperSR and the Total Station is that the Total Station is not physically moved to each data point. Instead a piece of surveying equipment called a prism pole is moved to the desired collection point and a laser is shot from the Total Station to the prism pole and back to the Total Station to measure elevation data. The first thing that must be done before collecting elevation data with the total station is that it must be properly set up. Like the HiperSR the Total Station sits on top of a tripod, but the set up procedure is much more difficult. First an occupied point (OCC) must be flagged so that the total station can be placed directly over it. Second, the tripod must be placed over the OCC and the Total Station must be placed on top of the tripod. Both the tripod and Total Station have many leveling knobs that must be tweaked until they are both perfectly level and over the OCC. A laser plummet is used to make sure that the Total Station is directly over the OCC. Thirdly, two back sight points must be taken to zero out the Total Station GPS unit for true north. This is done by clicking on the back sight icon in the Total Station interface, entering in pertinent information such as prism rod height (2 meters), and physically taking the back sight points. Both the OCC and two back sight points were taken using the HiperSR GPS unit. It is important to set the height at two meters for the prism rod or every measurement taken by the Total Station will be skewed by the difference inputted for rod height. Once the Total Station has been zeroed out for north the Magnet program located on the Tesla interface can be utilized to collect elevation data. A full list of set up instructions can be viewed here in Appendix A. Below in figure three a tripod complete with total station and prism rod is pictured.
Transferring the Data
Once the campus mall elevation data was measured and recorded by both the Topcon HiperSR and the Topcon Total Station, My partner and I had to upload the data as text files. A tutorial for how to do this was provided by the University of Wisconsin Eau Claire's geospatial facilitator Martin Goettl. In a nut shell, I used the exchange function to transfer the job I created for both the HiperSR and Total Station topographic surveys into text files. The two text files created can be viewed in figure four below.
Figure 4: shows the two text files for the HiperSR and Total Station elevation data. This data is organized into longitude (easting), latitude (northing), and height (elevation). |
DISCUSSION
The final elevation maps were made up of the x, y, and z-data, a topographic base map, and a continuous raster surface created using the natural neighbors interpolation method. In figures five and six below elevation maps of the Topcon HiperSR and Topcon Total Station data can be viewed respectively.
Figure 5: shows an elevation map of UW-Eau Claire's campus mall. This map was created using the data collected with the Topcon HiperSR GPS unit. |
Figure 6: shows an elevation map of UW-Eau Claire's campus mall. This map was created using the data collected with the Topcon Total Station GPS unit. |
CONCLUSION
Overall this was a tough field exercise due to having to work with unfamiliar and complicated equipment. Working with the HiperSR unit in tandem with the Tesla unit was actually a fun experience because they were easy to understand and produced accurate results. Working with the Topcon Total Station was a horse of a different color. The level of effort that goes into setting up a total station is astronomically higher than a HiperSR. Even though my partner and I inputted a lot of effort into the setup, the results of the Total Station elevation data were still highly inaccurate. I stated above that it is good to have a back up system and a broad base of knowledge when it comes to using surveying equipment, but if at all possible I would opt to use the HiperSR GPS unit for any and all surveying applications.
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