Microtopography Survey

Introduction

This week’s assignment was another surveying mission. The TopCon total Station was employed to collect elevation data for the University of Wisconsin – Eau Claire’s Campus Mall. The Total Station is a surveying tool (figure 1) which is commonly used by surveyors because of how accurate the results are (sub-meter). The Total station records in meters a northing, easting, and height. It works by shooting a laser to a prism which is held on a pole with a fixed height and by determining the angle and time it takes to travel to the prism and back it records the values.

Figure 1. The TopCon Total Station set up and ready to record survey points. The GPS unit on the front is connected via Bluetooth to the Total Station so as the total station records it is being sent to the GPS unit and plotted on a virtual map.

 We worked in a group of four to survey the campus mall which is a newly constructed green space which is along Niagara Creek. The mall is in the shape of a miniature amphitheater built with a gentle slope then once it reaches past a sidewalk it forms a steep decline to the creek.

Figure 2. UWEC's campus mall viewed from the West. From this angle you can see the gentle slope from northwest to southeast forming the amphitheater shape.

Methods

Data Collection

A total of 108 points were collected over the course of two hours. Weather conditions were chilly but tolerable. In our group of four we used a rotation which allowed everyone to gain experience using the Total Station to collect data. An occupied point was established before any data was collected. An occupied point is the position from which all other points will be measured (similar to the azimuth assignment). Data collection first used a circular patter following the sidewalks around the campus mall but then changed to a side to side method. The 108 points collected can be viewed in figure 3 below.

Figure 3. A map showing the location of all 108 points recorded and a special symbol showing where the Total Station was positioned during the survey.

Results

The kriging method was used to create a digital elevation model (DEM) from the points. Below in figure 4 is the DEM of the campus mall.

Figure 4. A DEM created using the kriging interpolation method. Notice how the slope on the mall appears to have a sharp break running almost perfectly along the NW-SE line.

Since the model has an elevation associated with it the DEM can viewed in 3D in ArcScene. ArcScene is able to create 3D models from any data set with any kind of value such as elevation or demographic info per county, block group, state, etc. A 3D model with a view from the south of the campus mall was created and includes a figure to show where the occupied point was located (figure 5)

Figure 5. The DEM displayed in ArcScene with the aerial image overlaid and clipped to the size of the DEM. This image is of the mall when viewed from the south.

 

Discussion

The goal of this lab was to familiarize ourselves with the TopCon Total Station and to learn a new form of surveying. Throughout the survey the group discussed how to better collect points and where to collect more data to capture the micro-topography. Since we switched how we were collecting data it was difficult to decipher where we needed more data collected so once we reached 100 points we collected a few more along the stream to help increase the size of the study area.

One major issue we ran into while processing the data was that once in ArcMap all of our points minus the occupied point were 180 degrees off. To correct this error we started an editing session and selected all of the point. Then we chose the rotate tool in the editor toolbar and set the occupied point as the anchor point then rotated all of the points by 180 degrees around the occupied point. This completely corrected the error then we were able to go ahead and create the DEM.

Another issue was that all of the points appeared to be over a meter north of where they were actually taken. This error could be due to numerous factors but most likely because of how the occupied point was measured with a GPS which was not up to par with the rest of the Total Station.

Conclusion

If given more time, a more thorough survey would be conducted and the points would be included with the previous survey. The error discovered while processing data was because we used the back sight instead of the front sight when setting up the Total Station. The back sight should have only been used if we were to have moved the Total Station but because there was no interference we did not need to move it. The DEM created shows the gentle slope on the campus mall and where points were taken closer together it is more accurate. The TopCon Total Station is a magnificent tool and it is no wonder why it is used in road surveys by engineers.