Introduction:
In Field Activity #8 data was recorded by building a geodatabase, and deploying it to a Trimble Juno GPS unit. However there a couple of deficiencies with this method. If your project requires a high degree of accuracy, other methods should be employed.In addition, you do not have the capability to capture accurate elevation data. Field Activity #8 required us to try to ascertain snow depth, but this was done by sticking a rudimentary meter stick down into the snow until it reached ice pack, or ideally, the ground. This method sufficed for our purposes but would not be suitable information for more formal reports.
The Topcon Total Survey Station (as seen in Figure 1) is an ideal surveying instrument for recording preciseelevation data.
Figure 1: The Topcon Total station is a technologically advanced surveying instrument
Figure 2: The Topcon GMS-2 handheld unit is used in coordination with the Total Topcon Total Station
Study Area:
Nestled between several UW- Eau Claire campus buildings, an approximately 1 hectare campus green space (as seen in figure 3) slopes down toward Little Niagara Creek. Our job will be to measure elevation in this general area.
Figure 3: This UWEC green space will be the subject of our Topcon survey. Note that it slopes down toward Little Niagara Creek just visible under the bridge in the left-background
Methods:
Setup
It is essential that the Topcon Total Station be stable and level for accurate surveying. First, the tripod legs must be spread out wide enough to provide a very strong base for the heavy total station that will be placed upon it. Next, each leg should be grounded to secure it. To accomplish this, stakes at the bottom of each leg are driven into the ground by pressing on the "ledge" attaches to each stake.
Each leg of the tripod can be adjusted as needed to provide a level surface for the Topcon Total Station. The Station is literally attached by screwing it into the tripod with a piece that is removed before and attached after placing the unit onto the tripod.
In order to determine whether the total station is level, three circular black knobs at the bottom of the unit (as seen in Figure 4), and corresponding with each leg, are adjusted for calibration. It may be necessary to adjust the legs further to calibrate the total station precisely, as well.
Figure 4: Basic features of the Topcon Total Station along with circular knobs at the bottom of the unit for calibration to ensure the unit is level
In addition there are three actual levels (similar to the one seen in Figure 5), one for each leg, to provide direction while calibrating.
Figure 5: A level similar to this coordinates with each leg of the tripod to guide your calibration
After the unit was level, it was important to record the level from the lens to the ground directly beneath it. This data should be recorded for entry into the GMS-2
There is a cover on the total station lens that must be removed - this is a rather easy step to overlook
The Total Station was then turned on, and one more check of the level of the entire system is accomplished by looking at the tilt.
Once this is accomplished, there is a laser plummet that projects onto the ground, It should be checked to ensure the unit is located in the exact point desired. This is especially important if you have to move the unit and take measurements from more than one location.
After following these steps, it was necessary to turn on the Bluetooth with the total station. The command process is as follows (Menu--> F4 --> F4 --> F2 --> F4 --> F4 --> F3 --> "Enter" to set).
With the Bluetooth on, a new project was created on the handheld GMS-2 and the ideal coordinate system for the particular zone of Eau Claire we were in was chosen. . Before proceeding we needed to make sure the unit recognized the Bluetooth on the total station.
Back-Site
We were then ready to set our back-site and occupied point. This was done by having a member of our group go to a location holding a prism pole (as seen in Figure 6)
Figure 6: The prism pole used to mark and measure survey points in coordination with the Topcon Total Survey Station
This location and a back-site are essentially "shot and marked" by the total station. In addition, a compass was used to ascertain the azimuth of this initial point and entered into the handheld GMS-2. At this point, the GMS-2 will request information for the height of the total station (as recorded in the set-up process) and the height of the prism pole reflector.
Our recording was as follows:
Total Station Height: 1.52 m
Prism Pole Reflector: 2 m
Azimuth: 322 degrees
Data Collection
Still using the handheld GMS-2 (in the Topsurv Software) we followed the following command sequence (Select --> Topo --> Measure). Now we were prepared to measure.
One member of our group stood at each point keeping the pole as still as possible (as seen in Figure 7) to help with collecting the point and data.
Figure 7: Nathan stands with the prism pole marking a survey point
Another group member stood at the total station peering through the scope to site the reflector on the prism pole (as seen in Figure 8).
Figure 8: Cody stands at the Total Station siting the reflector attached to the prism pole
This group member notified a third member holding the GMS-2 (as seen in Figure 8) when the location has been sited. At this point, 'collect' was selected on the GMS-2. Both the azimuth and elevation of the point in relation to the location of the total station are recorded by the GMS-2.
As we went along, the first point marker (Nathan) tried to develop intervals of paces to cover the distance from the top of the slope down to the Little Niagara Creek and beyond. Thus you will notice later in our elevation map the points collected appear to be in sequence. The interval arrived at was 8 steps.
116 points were collected in this way within our 1 hectare plot starting from the west and moving in north-south paths By developing a pattern, it allowed us to assure coverage of the campus green space.
Data Export
After collecting our data points, it was necessary to export the data from the GMS-2 to a computer so the data could be imported into ArcMap for interpolation. Within the GMS-2 use the following sequence ( Export --> To File). Data sets can be exported either as .txt or .shp files. The key it is to make sure both the projection and datum used in data collection is also selected during the export. The delimiter was also set to 'comma'.
After exporting the data, we opened it in Notepad just to make sure it was all correctly formatted. Seeing everything looked correct we exported the table which was then opened in Microsoft Excel.
Interpolation
From Microsoft Excel, our data was added to ArcMap. The Kriging method interpolation was applied to our elevation data to smooth out the area in-between points.
Results:
Having applied the Kriging Interpolation, a map was developed displaying our elevation survey (as seen in figure 9). As you can see, the height of elevation is located in the northwest corner and sloped diagonally down to the Little Niagara Creek from there. I think our points are distributed in a way where we can feel fairly confident that the map developed with an interpolation applied is an accurate representation of the elevation surface presented by the UWEC campus green area.
Figure 9: The elevation map developed with the Kriging method interpolation applied shows the slope of the area proceeding down to Little Niagara Creek
There are a couple locations where points bunched up; this was most likely due to providing each team member the opportunity to experience each part of the data collection process. In addition, there will some differentiation between the step interval of each person. Had we taken some additional time to map out a desired layout of points we may have been able to provide an even better representation, but looking at the results, it does not appear that our point locations have created any abnormal patterns.
Discussion:
While this process become almost painless once the Topcon Total Station was set up, it was a rather arduous process setting the occupy point. We were forced to forego data collection on our initial day. We ran into more of the same trouble at the beginning of our second day. On the handheld GMS-2, you need to click the 'HTC Set' button when setting up the occupy point. The button simply would not select and would eventually tell us to reboot the Bluetooth on the Total Station. Luckily, the total station shut down for some reason (not intentional). After turning the Total Station back on we were able to click the button to set our occupy point with no further Bluetooth messages.
Initially, I had a difficult time settling in on the location of the Prism Pole reflector when looking through the lens of the total station. I really had to settle myself down, focus, and actually take off my glasses before I was able to start zoning in on the reflector.
The other problem we ran into was when we exported our data. Both .txt and .shp files would only display the occupy point. For whatever reason the data we were collecting wasn't exporting into the data files even though everything seemed to be taking place as it should when we were in the field. Luckily, Martin Goettl, the geospatial technology facilitator, was able to locate our data and recomputed it.
Conclusion:
As is true with any precision instrument, the Topcon Total Survey Station requires preciseness in both set-up and execution of processes. Taking time to familiarize with the steps and reasons for the steps is the key to avoid getting stuck. If you take the time to carefully set up your process, you will eliminate a lot of stress, and help avoid errors leading to smoother data collection. Using a precise instrument is not a guarantee of precise results. It is completely dependent upon the operators executing the proper steps.
Also, having good communication between group members and understanding each other's roles can help the process along, and help you cover for one another.
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