Activity #9: Campus Mall Total Station Survey

Introduction

Figure 1 - Learning how to operate the Topcon
Total Station.

This exercise introduced our class to using the Topcon Total Station for doing topographical surveys. Each of our groups were instructed to survey an area roughly a hectare in size of anywhere on campus. Our class meeting on Monday consisted of learning how to set up and use the Total Station. In the classroom, we were shown how to set up and level the tripod and device. Then we went outside to learn how to gather data. From there, it was up to us to find times to meet as groups, check out equipment, and complete the survey.

The Total Station works by shooting a laser at a prism that is on top of a pole. The prism reflects the laser back and the Total Station can determine the location and topographical elevation by the angle of the laser and the time it took to travel. Typically, one person will hold the pole with the prism on it and one or two people will operate the Total Station. The person with the prism will stand in as many places as necessary to collect enough points.


Equipment

Topcon Total Station (Figure 2)

Figure 2 - Topcon Total Station

Topcon GMS-2

Figure 3 - Topcon GMS - 2

TruePulse 360 Laser Rangefinder

Figure 4 - TruePulse 360 Laser Rangefinder

Survey Area

Figure 5 - Location of UW- Eau Claire and study area.

Our group decided to do the new UWEC campus mall for our survey area (Figures 5 and 6). The aerial images are not up-to-date. The building within the red box in figure 6 was demolished and a new one constructed south of that location. The area within the red box is currently a grassy area with stone benches.

Originally, we wanted to do the same area of campus that we did for the distance azimuth survey. This area was too small and too crowded to do an effective survey, however. The campus mall is a wide open area that is more conducive to learning how to do our first survey.

The assignment called for surveying an area a hectare in size (100m x 100m). The area, however, did not get 100m in the north-south direction, so we extended the area east-west that we surveyed to get roughly the same area of coverage.

Figure 6 - Study area on campus. There are not yet any current
aerial images of campus. The area within the red box is an open,
grassy area with rock benches.

The following images (Figures 7- 10) are pictures of our study area.

Figure 7 - Facing north/northeast towards Schofield Hall

Figure 8 - Facing west/northwest towards McIntyre Library

Figure 9 - Facing southeast towards Roosevelt Ave.

Figure 10 - Facing southwest towards the Davies Center.

Methods

Figure 11 - Example of Total Station tripod setup.

To begin the survey, our group needed to set up and level the tripod as well as the Total Station itself. This would ensure that our measurements were accurate. The tripod legs need to be spaced equally apart and have a wide base to ensure stability (Figure 11).

Figure 12 - Leveling screw and circular level.

Next, the Total station can be placed on the tripod and screwed onto the top. Once the device is attached, it's time to level. There are two different areas to level: the circular level and the plate level. The circular level is calibrated by adjusting the length of the legs of the tripod until the bubble is in the center of the circle (Figure 12).

Figure 13 - Plate level.

Next is the plate level (Figure 13). There are three screws near the base of the device that can fine-tune the plate level (Figure 12). To get the bubble in the center of the plate level, face the device between two of the screws, turn one until the bubble is in the middle, then rotate the device to be in-between the next screws. Keep doing this until the bubble stays in the center of the plate level.

Figure 14 - Leveled Total Station ready to collect
data.

Once this step is done, both levels should be calibrated. Figure 14 shows a leveled, ready-to-go Total Station. The height of both the Total Station and the pole holding the prism are also measured and will be entered later.

First we used the GMS to gather a point directly below the Total Station. This would be used as our occupied point. The occupied point is the point that all the other data is collected from. If we have the location of this point, then everything we gather should be accurate (similar to the distance azimuth assignment we did earlier). We then had to set our backsight. We did this by using the TruPulse to find the azimuth to our backsight and label it as such in the GMS. We were then ready to start collecting data.

Figure 15 - Jeremy using the GMS to collect the points while I sight the
Total Station. Zach is circled in red holding the prism at the collection point.

For data collection, one of us held the pole with the prism at the point where data was being collected, one of us sighted using the Total Station, and the third group member used the GMS to record the data (Figure 15). We started in the corner of our study area nearest the library to the northwest and moved back and forth working our way towards the Total Station, then past it, to the southeast portion of our study area (Figure 16). Figure 16 also shows the points that we collected, 147 in total.

Figure 16 - The survey points that we collected, as well as arrows showing the direction and method of point collection.

Results

Our results seemed to be pretty accurate. It is difficult to tell in the figure 17 map (the aerial images are not up to date, so the Davies Center as well as Little Niagara Creek are not shown in the correct locations), but the area of lower elevation is where the campus mall slopes down to the creek. The rest of the survey area, while varying slightly, was mostly level.

Figure 17 - Results of survey interpolated using the Nearest Neighbor method. Range of elevation is from 236.263 - 239.263 meters above sea level.

Discussion

The difficult part of this exercise was setting up the total station. Our professor came out with us when we went to do the survey to show us how to navigate the menus and set up the device. The actual data collection was simple and just a matter of doing the same thing 147 times. The largest issue we encountered (and from talking with others, we weren't the only group that did) was that the Bluetooth connection from the Total Station to the GMS kept disconnecting. This was pretty frustrating, and we never really found out why this was happening. We just had to go back into the settings, reconnect, and continue.

We had intended to switch off roles so everyone got some experience with each, but we realized that the survey went quicker if we each did the same thing for the duration. We were able to get into a good rhythm that way, instead of trading off and having to get into a new rhythm each time. Also, when we leveled the Total Station, we did not take into account that the three of us are different heights. I started off as the one sighting through the device, and I am the shortest one in the group. Zach is much taller than I, and it would have been uncomfortable for him to have to bend over the whole time. We could have adjusted the station, but that also would have taken more time. While it was mostly sunny that day, there was a chilly wind. We decided to not break our momentum and finish the project as quickly as possible.

Luckily, we had no issues when exporting the data to the computer. It went smoothly, as did interpolation and map creation.

Conclusion

The results, while accurate, are a little boring to look at. There is only about a 3 meter range between the highest and lowest point, meaning the survey area was pretty level. This worked out well since we all were using this technology for the first time. Learning would have been slightly more difficult had we had a very diverse terrain. But a slightly greater elevation range would have at least made the resulting map more satisfying.

Terrain surveying is something that is always needed in various different work sectors. I like having a general understanding of the processes, but I hope to gain more knowledge in the future. When surveying larger plots and more dynamic terrain, the Total Station would have to be moved, adding extra steps to the process. This activity was only a brief introduction to land surveying.