This blog is a culmination of two weeks of activities that include various topographic survey methods. The first week we conducted a topographic survey using a dual frequency GPS and the second week we used the Topcon Total Station. For both of these methods, we had to become familiar with the units as well as go out and collect data points so we could display the topographic surveys through ArcMap.
Study Area:
Our class was tasked to collect these topographic data points in the Campus Mall, more specifically the Campus Amphitheater. We used the same location for each survey method so we could compare results along the same surface. This location is for the most part relatively flat but in some areas it does provide us with the change in topography needed to make topographic maps that stand out. This makes it easier for us beginners to practice using this equipment in easy terrain. As shown by Figure 1 below you can see that the study area is quite small compared to something of the Priory for instance. This will also allow us to eventually combine our results to make a larger or more detailed topographic map.
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| Figure 1: Map showing the location of the campus amphitheater in the UWEC campus mall |
Methods:
Like stated earlier, we used two separate methods in creating our topographic survey, one with a dual frequency GPS and the other with the Topcon Total Station. I will explain in detail both of these methods and we implemented them.
Survey with a Dual Frequency GPS
To conduct this survey we needed three essential pieces of equipment; The Topcon Hiper, Topcon TESLA, and a MiFi wireless router. These three pieces are connected to each other in the following ways; The Hiper is screwed on top of the surveying tripod with the TESLA unit attached midway on the rod so we could use it comfortably, and the MiFi had to be close enough so the TESLA could pick up its signal to connect to the internet.
Now that we properly connected all of the equipment together, we could begin our survey. To do this we had to create a folder in the TESLA unit so under Topo survey. Once all the parameters had been set we could begin data collection, of which we had two different options, the easy way or the hard way... The easy way or the "quick" way was less accurate but quicker because it takes anywhere from 3-5 points to average out where as the hard way or "solution" takes anywhere from 7+ points to average out which creates a more accurate survey point. When you use the solution method, you are also given the option to save or not save the point depending on how happy you are with the accuracy. In the interest of time we collected using the quick method because we needed to collect 100 points in a short amount of time.
The class had a problem with the universities subscription on the TESLA and as a result we could only use the unit while it was in Demo mode, which meant that we could only take a maximum of 25 points per job. This was no big deal since we just had to create four separate jobs, which also allowed us to become more familiar with the interface. Another point of interest is that every time we moved the tripod to a different point, we needed to level out the rod so that our accuracy was not thrown off.
Survey with the Total Station
The second way of surveying that we learned was using the Topcon Total Station. This system was mounted on a Tripod and once again connected to the TESLA unit. The advantage of the Total Station is that it corrects for elevation, GPS location data, and distance. This method is very similar to the distance/azimuth method of surveying we did earlier in the year. If you would like a refresher on distance/azimuth surveying methods then click the link to my blog for that post. http://nikanderson336.blogspot.com/2015/10/distanceazimuth-survey-methods.html
To set up the total station we first had to take two very important points. The first being the occupy points which is where the Total Station will be located and will be the "home base" for the remainder of the data collection. The other point that we had to shoot was the backsight point, this is essentially the "zero" for the Total station to use for calculating azimuth values. After we collect those points then we must put the Total Station over our occupy point and begin the tedious process of leveling the Topcon out. We must first make sure that the Total Station is at a height where it is comfortable for all group members to use without crouching or getting on your tippy toes. Once it is at the desired height we would roughly level out the tripod but using the actual tripod legs and the common level that is found on the Total Station. Once the rough level has been achieved we then moved onto a more precise level which required a very detailed look into the three sides of the base of the total station. We had to make sure that once we got one side leveled, we would turn the total station around to the other side but only use the one dial on the right side of the Total Station that we didn't touch previously. Otherwise every time we leveled out one side we would screw up the previous side we just leveled.
So now that everything is all set up we can begin data collection which is quite simple yet not easy. One person would man the Total Station while the other would take the reflector rod and move around to various points along the terrain that we are trying to get the Topo survey from. That person that is holding the reflector rod has to hold perfectly still so while the other partner is meticulously aiming the laser at the reflector, the reflector doesn't move and make the Total Station have to play keep up.
Once we completed surveying, we would export the data onto a flash drive off of the TESLA unit and then import that into ArcMap, which would allow us to make the great topographic products shown below. We did this the same way for both surveying methods.
Discussion/Results
We can see from the maps below (Figure 2 and 3) that both methods will get us a decent rendition of a topographic surface. The next questions we would ask would then be; how much money do you want to spend, what terrain are you going to be in, and what kind of accuracy are you trying to achieve? Each system has its advantages and disadvantages, but your decision as which to use should be solely based off of the situation that calls for the topographic survey in the first place.
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| Figure 2: Map showing the topographic surface created from using the Dual Frequency GPS |
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| Figure 3: Map showing the topographic surface created from using the Topcon Total Station |
Conclusion:
When it comes to making topographic surveys, the first questions that you need to ask are where and what is the intended accuracy. Throughout the semester we have now learned many different ways to create surfaces within ArcMap and various ways of how to survey those surfaces as well. Yes, in a perfect world you would like to take the Total Station wherever you go because of its accuracy and its simplicity but that thing is heavy, bulky, and wouldn't work out in the bush. For this reason you must decide which survey method best suits your project and then go from there. Both of the methods we used in this activity are great for the locations where we used them but if we were on a steep slope or far away from any accessible terrain, we would be shit out of luck if we had to carry this equipment around and then level them every time we wanted to take a point.
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