Topographic Survey vs. Total Station Elevation Survey Techniques

Introduction

Gathering elevation data using GPS can be done in many ways. In this lab we explored the use of using topographic surveying with a dual-frequency GPS and surveying using a total station. The topographic survey requires a tripod, Topcon telsa field controller, topcon hiper SR positioning unit, and the MiFi. The total station survey requires the topcon telsa field controller, topcon hiper SR positioning unit, the MiFi, and the Prism pole. Both methods have advantages and disadvantages which we explored in this lab.


Study Area

• Date: 12 November 2015 and 23 November 2015
• University of Wisconsin-Eau Claire Campus Mall (area between Little Niagara that run through campus and Schofield Admissions Building)
• Conditions: Partly sunny with some wind, Average temp. 44°F (retrieved from weather underground)

Methods
Materials
Topcon Telsa Field Controller
Topcon Hiper SR Positioning Unit
Topcon Total Station
MiFi
Tripod stand (with level)
Prism Pole

Figure 1. Telsa Unit

In order to start collecting data, the Topcon Telsa unit needed to be set up. We created a new job and entered the necessary information. Note that we used the projected coordinate system UTM 15N and recorded our units in meters. Otherwise, our group used the default settings while creating a new job.

For our elevation survey we created a code "ELEV" so that the points taken were recorded under this code and given a unique number.

After the job was created, we connected the Telsa controller to the Hiper unit using a blutooth connection. With the Hiper attached to the top of the tripod unit and the Telsa attached as well we could start data collection.

During the second part of the lab the total station tripod and unit was used and connected to the telsa unit through a blutooth connection. To achieve the connection a MiFi portable wireless device was used just like in the topographic survey.

Figure 2. Total Station Unit

Data Collection 
On the Telsa unit there are two ways to collect the data (precise or quick). We chose to have the telsa take the average of 10 points using the quick option. Each time we collected a data point we needed to move and level the tripod to collect accurate points.

We took 100 points throughout the campus mall. Our strategy for taking the points was to zig-zag the mall area and avoid the large stones (as they would skew the elevation data).


The second part of the lab we used the total station to take elevation data by setting up an occupied point, and one back site. The purpose of the occupied site is that you only have to level the total station once to collect points versus with the topographic survey needing to move the whole unit 100 times.

Figure. Leveling the total station

Twenty-four points were gathered using the total station method. The back site and occupied point were first recorded using the topographic method. This is done because the total station sits atop of the occupied point and uses the back site as a reference in case you want to collect data beyond the scope of the original occupied point.

Figure 3. Troubleshooting the
blutooth of the total station

To set up the total station we first had to level the whole unit using the three round knobs on each side of the unit. Later, we used the laser to ensure we were right on top of the occupied point.

Collecting data with the total station, it is required to find the cross hairs from the prism pole exactly in the middle while looking through total station lens. From there you are able to collect the point data by selecting the save button on the telsa unit.




Analysis

Figure 4. Successful data collection!

We imported the data from the telsa unit to a notepad file on a flashdrive. From there we were able to display the X,Y data. We set our header line as follows, Lat (Y), Long (X), and Elev (Z) to avoid confusion when exporting the data as a feature class.

For both the topographic survey and total station survey the kriging, natural neighbor, spline, IDW, and TIN tools were run for all of the points. In the topographic survey data from the entire class was used to display the elevation of the UW-Eau Claire campus mall area. In the total station lab only points from our group were displayed.

Metadata

Who: Ally Hillstrom and Morgan Freeburg

What: Collecting elevation data by using dual frequency GPS

Where: UW-Eau Claire Campus Mall 

When: 12 November 2015

Why: To practice gathering elevation data with GPS  

Metadata

Who: Josie Markham, Drake Bortolameolli, and Morgan Freeburg

What: Collecting elevation data using total station equipment

Where: UW-Eau Claire Campus Mall
When: 23 November 2015

Why: To utilize another way of collecting elevation data

Discussion

The topographic survey was an easy method of collecting elevation data, however, compared to using a total station unit, the topo survey was quite slow. Below in figures 5 and 6 are the spline analysis layered over a topographic basemap of the UW-Eau Claire Mall. I chose spline to represent both datasets because after analyzing all of the tools spline displayed the topography of the study area the best. 

The data analysis is similar in accuracy between the two methods. The total station map would appear more segregated if there were more points to run the spline analysis with. Because the accuracy is comparable, the total station method seems much quicker and you could gather many more points in less time than the topographic survey.   

Getting to the end point of the maps was no walk in the park, especially with the total station lab. In both labs my groups struggled to work the telsa unit. We spent a lot of time troubleshooting. This goes to tell it is necessary to be prepared for complications in the field. Regarding the total station data collection we had to go out to the field three times in order to successfully collect the elevation data. Each time we went out we would get stuck on the next step. 

Our first challenge was the blutooth of the total station would not hold its signal. We had all the equipment set up and ready to go; the blutooth was even conected to the telsa unit. Once we tried shooting our back site the connection to the blutooth was lost. After that we spent fourty-five minutes turning the telsa and total station on and off (alternating the order) and trying to find our mistake in the settings. 

The next time we went out to the field we had all the equipment set out again, blutooth connection secure and the telsa turned off and would not respond. Finally, our third time in the field we were able to correctly arrange the equipment and the connections, but the telsa would not capture the point. Thankfully, it took less time to figure out the issue was focusing the crosshairs, and we were able to collect all of our points. Through our frustrations we became experts in setting up the total station over the occupied point in one try and leveling unit, but the telsa is the object that held us back. Unfortunately, technology fails sometimes.

Figure 5. Points collected from topographic survey and analyzed using the spline tool of ArcMap. 

Figure 6. Points collected from total station survey and analyzed using the spline tool of ArcMap.

Conclusion

Even though my group had our fair share of frustrations through out this activity it was incredibly useful to see the difference between the topo survey method and the total station survey method. Once again we learned technology is not perfect and may take a lot of troubleshooting, but in the end when it does work it makes collecting data much easier and efficient. The advantages of the topographic survey was it could be carried out with one person and does not require as much initial set up time. Again, I would favor the total station even though it requires at least two people and has greater set up parameters, but the ease of collection after is so much more efficient.