Activity 9: Surveying with a Topcon Total Station and GMS-2 GPS Unit

Introduction

The last couple of weeks we have been working on two different but very similar projects. Dr. Hupy assigned us to use a couple of different pieces of technology to collect elevation data of the campus mall here on the UW-Eau Claire campus between the Davies student center and Schofield Hall. The two different equipment pieces we used were the Topcon Total Station (Figure 1) and the Topcon Tesla GPS unit (Figures 2,3,4). With both of these pieces of equipment we were to collect elevation points and create interpolated surface maps with the results of each and compare the two methods of data collection. A previous activity where we collected distance/azimuth data is a simple way to do what we are doing with these high tech units however we did not collect elevation data which is vital for creating interpolated surface maps. These high tech units increase accuracy in most cases and give you that important elevation measure at a very high accuracy. These high tech units are costly however. They are expensive costing thousands of dollars and it is very time consuming and inconvenient because of the amount of equipment you have to bring with you to conduct the survey and collect the data. The complexity of these units is much greater as well so knowing when to use them compared to just doing a simple distance/azimuth survey is important.

Figure 1 This is the total station. It is used to conduct a surface survey as it can provide distance/azimuth and elevation data with high accuracy. This is a very pricey unit with a cost of 5 to 6 thousand dollars.

Figure 2 This is the Telsa GPS survey grade unit. This is the main console with all the different programs and tools installed on it. It is both WiFi and Bluetooth enabled which is why we need a MiFi console Figure 4. This is where you create files to store the data collected.

Figure 3 This is the GPS part of the unit. This communicates with the console above through Bluetooth. This will give you 2 to 3 millimeter accuracy of the location of data points being corrected. Elevation or Z values are also very accurate when collected with this unit.

Figure 4 This is a MiFi unit. This uses a 4G cellular connection to provide WiFi signal for up to 15 devices. This is used with the Tesla unit to increase location accuracy and enable wireless data transfer.

There is alot of new technology and processes to learn for this activity and that is why we spent basically a whole class period learning from Dr. Hupy how to operate these units. Set up and use of these units is a little tricky and needs to be repeated a couple of times before the work flow becomes easier. First we started with a general overview of the units and their purpose and Dr. Hupy emphasized the importance of being careful with them and handling them with care because they are very expensive. Another key point he emphasized is the importance of making sure both the Tesla and total station are level when data is being collected. This takes time. Through adjusting the tripod legs and black knobs on the total station it is leveled and when using the Tesla just tilting the pole until the circle level is inside the ring will do the same. The total station was definitely more difficult to level off. After the units are leveled Dr. Hupy explained how to collect the data which I will explain later in the Methods section of this post. 

Each group was to collect 50 points per person with the Tesla GPS unit and as many as we saw fit with the total station. My group collected 150 with the Tesla and 50 with total station. This data was then imported into ArcMap and surface maps were created from it.

Study Area

The area Dr. Hupy wanted use to collect data in is what we refer to as the campus mall Figures 5. It is a large open area in the middle of lower campus. It is fairly flat for the most part with little elevation variation however the whole area is pitched towards the south and the Little Niagara Creek Figure 6 that runs through lower campus next to the Davies student center. This activity was delayed because of  rain and poor weather in which these units should not be used in. The days data was collected were sunny spring days in the mid to upper 60s with little wind.

Figure 5 View of the campus mall from the occupy point during our total station data collection. Schofield Hall is on the right and Davies Center is on the left with the library at the end.

Figure 6 Little Niagara Creek runs through the middle of the campus mall past Davies Center.

Methods

Total Station Collection

First step to collecting our data was check out the equipment from the Geography department here on campus. We then walked from Phillips Hall to the campus mall to set up the total station. Before the total station was put in place and leveled two points had to collected with the Tesla. These two points are called the occupy and bascksight points. The occupy point is where the total station would be set directly above and stay during the duration of the data collection. The backsight point is recorded to give the total station a zero point from which to calculate the azimuth values. This backsight point is what the total station will record as North. Once the location of these two points is recorded the total station can be setup and leveled off to start data collection. The first step in setting up the total station is opening up and tripod that the station sits on. Then the station is mounted to the top and screwed into place. Then using the built in laser on the station we made sure that the station was directly over the occupy point location collected earlier. Once this is done then the tripod legs can be pushed into the ground and the leveling processing can begin. There is a circle level on the tripod stand and the key to making sure the stand is level is to get the bubble into the center ring of the level. This is done by slowly sliding the tripod legs one at a time up or down. Once the stand is level the next step is to level the total station itself. There are two tubular levels one on each side of the unit. There are 3 black knobs on the bottom of the unit at each corner. When turned these move the unit up and down slightly allowing you to level the unit. 

Once the unit is leveled the collection can begin. The total station is connected via Bluetooth to the Tesla console (Figure 2) which caused a lot of headaches for most groups. Once connected a new job is created where the data points will be stored. In order for the collection locations to be accurate the occupy and backsight point are entered in the file setup. It also asks for a height of the station off the ground as well as the height of the reflector (Figure 7) off the ground. In our collection the total station was 1.55 meters off the ground and the reflector was 2 meters up. Making sure these heights stay consistent during data collection is vital for accurate elevation measurements. Once this is all set up point collection begins. 3 person groups are ideal for this exercise so that one person can focus the total station, one can walk with the reflector pole and one can record the points in the Tesla console. Point collection was fairly easy after setup was complete. To collect a point the person holding the reflector picks a location and then holds as still as possible facing the reflector as straight back at the total station as possible. The person at the total station then uses the top sight to find the general location of the reflector. Then looking through the scope and using the adjustment knobs to move the scope up, down, left and right the cross hairs are placed on the center point of the reflector. Once the crosshairs are locked on the person on the Tesla console taps the collect point button. The total station will then collect the azimuth, distance and elevation for that point. This process is repeated for as many points as the user desires. We collected 50 points in approximately 30. Getting the crosshairs locked in is the most difficult and time consuming part of collection but the more you do it the better you become at locating the reflector and locking on.

Figure 7 This is the reflector that the total station shoots the laser beam at to calculate distance when taking the survey. It is hard to see but there are 3 lines that intersect in the middle of the scope and that point is where you want to line up the crosshairs of the total station scope on to get an accurate reading.

Tesla GPS Collection

The data collection with the Tesla GPS unit was much simpler and quicker. The GPS unit Figure 3 is mounted on the tripod with the MiFi velcrod to the pole and console either attached to the pole or carried. The MiFi, GPS and console are all powered up. Once the console is connected to the MiFi connection the GPS can be connected to the console via Bluetooth just like with the total station. Once everything is connected the next step is to create a new file to store the collected data in. Then inside that file collection begins. In order to collect the points the tripod is leveled using the circle level attached to the tripod. Once it is level all you have to do to collect a point is tap the collect point button on the console. We did this for a 150 points throughout the mall. It took about 2 hours to collect the points just because there were so many. The setup is simple and collection is easy.

Results

Once the data was collected using each method the files were dumped onto a computer in the form of a text or .txt file. This files include the latitude, longitude, height and name of each point that was collected in the field. Once the text files are of the console they are imported into ArcMap. They show up as a bunch of points on the map but when the interpolation tool is used a surface elevation map is created in both 2D and 3D. Figures 8,9,10 and 11 below are the resulting maps from the two surveys.

Figure 8 This is the interpolation of the points collected with the Tesla GPS unit. I used the Kriging interpolation method to create this map. You can see the elevation change of the campus mall from this 2D map.

Figure 9 This is the interpolation of the points collected with the total station. I used the Kriging interpolation method to create this map. You can see the elevation change of the campus mall from this 2D map.



Figure 10 This is the 3D surface map of the campus mall collected with the Tesla GPS unit. I exaggerated it by 2 to make the elevation change more apparent because it is really hard to see using the actual elevation values. This unit captures the surface a little better probably because there are 3 times the number of points in this model than there are in the total station model.  As you can see the campus mall is a pretty flat area.




Figure 11 This is the 3D surface map of the campus mall collected with the total station. I exaggerated it by 2 to make the elevation change more apparent because it is really hard to see using the actual elevation values. This representation isn't as accurate because there are much fewer points used in this model. The weird point that is in this image is most likely where the total station was sitting while collecting this data. That point is obviously an error created by ArcScene.

Discussion

Both of these units and data collection methods are important to know how to do and very applicable in real world situations. One is obviously easier to do than the other. The total station has a much higher cost associated with it. Not only does it cost a large amount of money but the time and knowledge that is required to use is also very high. The frustration and time wasted while trying to get it all set up properly and get everything on the total station and the Tesla console to work together was a big annoyance and set back. It took us about twice as long to get everything set up and working than it did to collect our survey data. This goes back to what Dr. Hupy told us a couple of weeks ago that the more technology you are relying on the better chance that it won't work. That is why knowing how to do a distance/azimuth survey with very little technology is a good skill to have. Even when Dr.Hupy was doing demonstrations in class of how to use the units they weren't always working right. He wasn't doing anything wrong that is just what happens many times when working with high tech equipment. The biggest problem we ran into is getting the Tesla console to connect to the total station via Bluetooth. I turned them both on and off a couple of times before they finally connected to each other. Once it was connected everything went smoothly. Setting up the tripod for the total station was also a little tougher than I thought it would be. Getting it level was difficult. Overall the total station is a longer more involved and frustrating process.
Using the Tesla GPS was much easier in my opinion. Everything connected the first time we tried and with this unit one person could have collected all the data. You don't need three people. The data collection went much faster because you didn't have to find the reflector every time you collected a point. Getting the tripod level was the biggest part of the work for this method. This process can be sped up by not using two of the legs on the tripod and just using the center pole with the level on. Simply holding that middle pole and leveling it allows you to move much more quickly than trying to level out all three legs at every point. Being careful to keep the pole steady while collecting the points is the biggest concern when collecting data in this way. The Tesla GPS overall was much quicker and user friendly in my opinion there was much less equipment to bring with you, fewer moving parts, less back and forth between devices and less human input required.

Conclusion 

This semester we have now learned the low tech way (azimuth/distance) and high tech way (total station and Tesla GPS) to conduct a survey. Both ways have advantages and disadvantages and the usefulness of each is dependent on the situation. However if it is accuracy that you want which is the case most of the time I would chose the high tech method. Even though it can be more time consuming and frustrating the results tend to be much more accurate and reliable. It also provides you with elevation data without which creating surface models like we did in this activity would be much harder or even impossible. This activity taught us how to use these new technologies, work together in teams and again do some more work in a GIS sharpening those skills. Overall a good exercise it was frustrating at times but the end result that can be created from this highly accurate data what makes the activity useful.