During this activity I practiced using survey grade equipment to gather topography data. of my study area of the University of Wisconsin-Eau Claire Campus Mall. Our goal was to collect 100 GPS points that include a coordinate grid location and elevation data, and process them in ArcMap to display the elevation through the survey site. The method used to collect this data are detailed below.
Methods:
Dual Frequency Survey:
For this lab we began by choosing a survey area of about 25m x 25m. My partner Morgan and I choose to survey the UW-Eau Claire campus mall. I began our survey process by establishing our own wifi hotspot by using a Version 4g MiFi unit. Next, we began configuring the Telsa. During this, we used the Magnet application however because of technical difficulties we were forced to use the demo mode. Although the functionally of the GPS survey was unaltered, we were only allowed to store 25 points per "job". This required us to make 4 different jobs. Within each of these, we specified the configuration for the GPS survey, such as the projection (UTM Zone 15N), datum (NAD 83 [2011]), and grid as the coordinate type . After this, we clicked on the Connection tab. Within here we were allowed to Bluetooth to the Topcon Hiper SR RTK. After this connected, we clicked on the Survey tab. From here we selected Topography, which brought us to a screen that allowed us to take GPS points.
From here we were able to set up the tripod. The Topcon Hiper was located on top of the pole, and the Tesla was locked into a extended arm in the middle of the pole. Looking at our area, we sectioned it in roughly 4 equal parts and took 25 points in each. At each location we decided to take a point, we leveled out the tripod using the attached level. Once the tripod was balanced we saved the point. We repeated this process 100 times to end with 100 GPS points.
After the survey was complete we disconnected the Tesla from the Hiper and went inside to export the data. To export the data we saved it on a jumpdrive. The file format was saved as a text file, which we were able to view on the computer in the Notepad application. In order for our data to be organized correctly in Arcmap, we were required to edit the header of the Notepad document. I chose to label the header with: Name, Long(X), Lat(Y), Elev(Z). I also chose to copy all the data into one document. Both of these change made it easier when importing the data into ArcMap. To display the data I selected display XY data, followed by Export Data. The GPS points can be seen display in figure 1. Next, to display the elevation of this study area, I ran the Natural Neighbor tool. The output is displayed within figure 2.
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| Figure 1: The 100 GPS points take in the University of Wisconsin-Eau Claire Campus Mall using the Topcon Telsa and Topcon Hiper. |
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| Figure 2: This figure displays the 100 GPS points take in the University of Wisconsin-Eau Claire Campus Mall using the Topcon Telsa and Topcon Hiper, and the natural neighbor output ran on the point feature class. This output displays the area's elevation data in meters. |
Total Station Survey:
For this lab we went to the same location of the UW-Eau Claire Campus mall, used within the Dual Frequency Survey. I began our survey process by establishing our own wifi hotspot by using a Version 4g MiFi unit. Next, we began configuring the Telsa. During this, we used the Magnet application again and located to survey to begin a topography survey, while setting up a job the with the same settings as the Dual Frequency survey above. Using the Telsa and Topcon Hiper, we took three separate gps back sight points which will be used to set the north bearing for the total station. Next we set up the Total Station at our point of origin. This required a lot of small adjustments to balance the equipment. Once this was step up, we powered down the Telsa to Bluetooth it to the Total Station, however the Telsa would not turn back on. This forced us to come out a different day to survey the remain 22 survey points. The following week we resumed our survey using the Total Station. To take each point, my job was to focus the lens to the reflector that my team member Grant was holding. He staggered himself in 22 different locations with our survey area. After our job was full of 25 points, including the Occupy Point (Origin), and the three back sights, we headed indoors to export the data on a jump drive. This allowed us to download the data on a flashdrive and save it as a text file. Once again, I edited the textfile heading, and imported the points into ArcMap. The displayed Total Station GPS point can be seen in figure 3. My next step was too run the Natural Neighbor tool in ArcMap to generate a DEM for this survey. The results can be seen in figure 4.
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| Figure 3: The 25 GPS points taken in the University of Wisconsin-Eau Claire Campus Mall using the Topcon Total Station. |
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| Figure 4: This figure displays the 25 GPS points take in the University of Wisconsin-Eau Claire Campus Mall using the Topcon Total Station, and the natural neighbor output ran on the point feature class. This output displays the area's elevation data in meters. |
Metadata (Dual Frequency):
Who
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Ally Hillstrom, Morgan
Freeburg
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What
|
Survey Grade GPS
Survey (Dual Frequency Survey)
|
When
|
Collected on Tuesday,
November 10th
|
Where
|
The UW-Eau Claire’s Campus
Mall, Eau Claire, Wisconsin
|
How
|
GPS Points collected
using Topcon Hiper and Topcon Telsa, along with Verison MiFi unit to create a
hotspot.
|
Metadata (TotalStation Survey):
Who
|
Ally Hillstrom, Grant
Muehlhauser, and Matt Brueske
|
What
|
Survey Grade GPS
Survey (Total Station Survey)
|
When
|
Collected on Tuesday,
November 16th
|
Where
|
The UW-Eau Claire’s Campus
Mall, Eau Claire, Wisconsin
|
How
|
GPS Points collected
using Topcon Hiper and Topcon Telsa, TotalStation, along with Verison MiFi
unit to create a hotspot.
|
Discussion:
This assignment gave insight into two different ways of completing a topography survey. The dual frequency survey was a much faster way of surveying, at least for a beginner, because the set up required less time than the Total Station. The Total Station requires much more practice and time to set up, because you must have the equipment perfectly balanced. The environment also would influence the type of survey technique you would want to use, because it would be very difficult to balance the Total Station survey if you are surveying on top of sand, which is likely to move under the equipment.
When comparing Figure 2 and Figure 4, the Dual Frequency output appears to have displaying the DEM more accurately however we took 100 points for this survey, compare to only 25 points in the Total Station survey. If I were going to redo these surveys, I would like to survey with the same amount of points with each technique, in the same size area. Figure 3 and 4 make it clear that there are gaps in the Total Station survey where additional survey points could have been taken. Knowing there were a few open areas in the data, I chose natural neighbor knowing it uses the closest input samples and applies weights to them based on their proportion of area. This interpolation also fit to boarder of my data points, unlike others such as spline that extended the interpolation to other areas without data points. Running these interpolations made it clear that it is necessary to have points equally displaced through out the survey area. Although my data isn't in depth enough to comment of the accuracy of each method, according to the College of Engineering at the University of Saskatchewan, the total station method is less accurate than the dual frequency methods. It is also important to keep in mind that the Total Station requires at least two people to complete the survey, where the dual frequency survey could be completed independently.
Conclusion:
During this lab, we practiced completing a dual frequency and Total Station topography survey. This gave an experience with setting up the configurations of the equipment before surveying, surveying with each techinique, and manipulating and interpreting the data in ArcMap, and comparing the outputs of the two survey techniques.
Sources:
page 256: http://www.engr.usask.ca/classes/CE/316/notes/CE%20316%20Ch%207%209-3-12.pdf
http://resources.esri.com/help/9.3/arcgisengine/java/gp_toolref/spatial_analyst_tools/how_natural_neighbor_works.htm
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