Field Exercise 9 - Topcon and Total Station Topographic Survey

INTRODUCTION

          For field exercise nine a partner and myself were tasked with carrying out two topographic surveys of UW-Eau Claire's campus mall. The first topographic survey was measured and recorded using a Topcon HiperSR GPS unit and a Topcon Tesla unit, and the second topographic survey was measured and recorded using a prism pole, Topcon Total Station, and Topcon Tesla unit. The purpose of this field exercise was to create elevation maps of the UW-Eau Claire campus mall, and get students familiar and comfortable using modern surveying equipment.
          There were three reasons why my partner and I were required to conduct two different topographic surveys of UW-Eau Claire's campus mall. The first reason as discussed in previous blog posts is to always come prepared with a back up plan in case of equipment failure in the field. One piece of equipment or method may not work for every surveying scenario so it is a good idea to come prepared with back ups. The second reason for conducting two surveys of the same area of interest (AOI) is that after both surveys are conducted my partner and I could compare the two sets of data to see which method ended up working better than the other. The third reason for conducting two different surveys is that a lot of firms have budget constraints and aren't able to afford the newest surveying technologies. If this is the case it is important to be able to use older equipment and methods to get the job done.

STUDY AREA

          The study area for field exercise nine was the UW-Eau Claire campus mall. Surrounded by Phillips hall in the southeast, the Davies Center to the south, McIntyre Library to the west, and Schofield Hall to the north, the campus mall is located in the center of UW-Eau Claire's lower campus. The UW-Eau Claire campus mall's position can be viewed relative to the surrounding academic buildings below in figure one.

Figure 1: shows the campus mall which is outlined in red. Both topographic surveys are to be conducted on the campus mall for field exercise nine

Due to its flatness, openness, and relatively small size the UW-Eau Claire campus mall is an easy area for students to survey. The only bad thing about surveying the campus mall is that it sees a lot of foot traffic during school hours due to its central location. This did not pose much of a problem when using the Topcon HiperSR GPS unit because lasers were not used to shoot positions, but when using the Topcon Total Station the laser that shot out to the prism pole was constantly interfered with by pedestrians. This interference may or may not have effected the integrity of the Topcon Total Station's data.

METHODS

          The first thing I'll run through in the methods section is the four different pieces of surveying equipment used: the Topcon HiperSR GPS unit, the Topcon Total Station, the Topcon Tesla unit, and the prism pole. I will also discuss how my partner and I utilized each piece of equipment.

The Topcon HiperSR

          The Topcon HiperSR unit works in conjunction with the Topcon Tesla unit to measure and record elevation data. both pieces of equipment connect to each other via a mifi unit which allows them to communicate. The HiperSR unit is mounted on top of a tripod of known height so that the unit can accurately record elevation data, and the Tesla unit is mounted on the side of the tripod so that the surveyor can record data points at the touch of a button. The way this unit works is that it is physically moved around by the surveyor to each point he/she wants recorded. The unit is then leveled using a bubble level built in to the tripod to make sure that the Topcon HiperSR unit is directly above the desired point. Once the tripod is made level the surveyor elects for the unit to record a point using the Topcon Tesla interface. A Topcon HiperSR unit attached to a tripod is pictured in figure two below.

Figure 2: shows a Topcon HiperSR unit attached to the top of a tripod. The Topcon Tesla recording unit is also located in the middle of the tripod. It should be noted that it is through the HiperSR unit (top of tripod) that the data points are measured and it is through the Tesla unit (middle of tripod) that the data points are recorded.

          In order to begin recording data points with the HiperSR and Tesla units my partner and I first had to create a new job (geog336_toposurvey_group3). The unit then asks for a coordinate system to project the data in. My partner decided to project using the UTM 15 North projection. We then created a point feature to use for when we actually start recording data points. After setting up our job, projection, and feature class it was simply a matter of setting up the tripod and recording the points using the Tesla interface. My partner and I set our point collection interval at five points. This meant that for every data point we collected the HiperSR unit took five points and averaged them for increased accuracy. My partner and I were supposed to take a total of 100 points to effectively cover the entirety of the AOI, but due to rain we were only able to collect 90 points. This did not greatly effect the integrity of our data, however, because we still were able to collect data points throughout the entire campus mall.

The Topcon Total Station

          Like the Topcon HiperSR the Topcon Total Station worked in conjunction with the Tesla unit to measure and record elevation data. The Total Station and Tesla unit also connected via mifi in order to communicate with each other as well. The difference between the HiperSR and the Total Station is that the Total Station is not physically moved to each data point. Instead a piece of surveying equipment called a prism pole is moved to the desired collection point and a laser is shot from the Total Station to the prism pole and back to the Total Station to measure elevation data. The first thing that must be done before collecting elevation data with the total station is that it must be properly set up. Like the HiperSR the Total Station sits on top of a tripod, but the set up procedure is much more difficult. First an occupied point (OCC) must be flagged so that the total station can be placed directly over it. Second, the tripod must be placed over the OCC and the Total Station must be placed on top of the tripod. Both the tripod and Total Station have many leveling knobs that must be tweaked until they are both perfectly level and over the OCC. A laser plummet is used to make sure that the Total Station is directly over the OCC. Thirdly, two back sight points must be taken to zero out the Total Station GPS unit for true north. This is done by clicking on the back sight icon in the Total Station interface, entering in pertinent information such as prism rod height (2 meters), and physically taking the back sight points. Both the OCC and two back sight points were taken using the HiperSR GPS unit. It is important to set the height at two meters for the prism rod or every measurement taken by the Total Station will be skewed by the difference inputted for rod height. Once the Total Station has been zeroed out for north the Magnet program located on the Tesla interface can be utilized to collect elevation data. A full list of set up instructions can be viewed here in Appendix A. Below in figure three a tripod complete with total station and prism rod is pictured.

Figure 3: shows a total station mounted on top of a tripod and facing a prism rod. To take an elevation point with a total station it must be directly facing the prism rod. When the point is taken a laser is shot from the total station to the prism rod which then reflects the laser back to the Total station which records the elevation at which the laser shot back at.

              Before my partner and I began collecting points with the Total Station we initiated the setup procedure described above including the collection of the OCC and two back sight points. My partner and I then split the surveying job into two tasks with one person manning the Total Station and the other manning the prism rod. The person manning the Total Station used the Tesla unit and the Magnet program to record data points measured by the Topcon Total Station and prism rod. The person manning the prism rod physically moved the prism rod around the campus mall in order to collect elevation data around the entirety of it. For this topographic survey my partner and I were not required to take 100 data points; instead, we were simply tasked with taking a representative example of the campus mall's elevation. This ended up being 45 data points.

Transferring the Data

          Once the campus mall elevation data was measured and recorded by both the Topcon HiperSR and the Topcon Total Station, My partner and I had to upload the data as text files. A tutorial for how to do this was provided by the University of Wisconsin Eau Claire's geospatial facilitator Martin Goettl. In a nut shell, I used the exchange function to transfer the job I created for both the HiperSR and Total Station topographic surveys into text files. The two text files created can be viewed in figure four below.

Figure 4: shows the two text files for the HiperSR and Total Station elevation data. This data is organized into longitude (easting), latitude (northing), and height (elevation).

After I transferred the data into text files I uploaded it into ArcMap as x, y, and z data. The x-data corresponded to the longitude (easting) data, the y-data corresponded to the latitude (northing) data, and the z-data corresponded to the height (elevation) data. To import the x, y, and z-data I simply clicked on the add data and add XY data tabs located under the ArcMap file tab. Once the x, y, and z-data was uploaded I could create elevation maps.

DISCUSSION

           The final elevation maps were made up of the x, y, and z-data, a topographic base map, and a continuous raster surface created using the natural neighbors interpolation method. In figures five and six below elevation maps of the Topcon HiperSR and Topcon Total Station data can be viewed respectively.

Figure 5: shows an elevation map of UW-Eau Claire's campus mall. This map was created using the data collected with the Topcon HiperSR GPS unit.

Figure 6: shows an elevation map of UW-Eau Claire's campus mall. This map was created using the data collected with the Topcon Total Station GPS unit.

          Looking at the two maps in figures five and six above it should be noticed that one of these maps turned out much better than the other. The map in figure five showing the HiperSR elevation data is much more accurate and comprehensive than the map in figure six which shows the data collected with the Topcon Total Station. The map in figure five shows a good representative example of elevation data throughout the campus mall, the points are nicely spaced out, and none of the data points appear out of place. The map in figure six however is a different story. The survey does not showcase a good representative example of elevation data throughout the campus mall, the data points are clumped and unevenly spread out, and some points even appear inside buildings. the data discrepancy in figure six could have come from a number of different reasons with human error being at the top. My partner and I may have set up the two back sights incorrectly and it's entirely possible that the skewing of the data was caused by improperly setting up the Total Station. As stated above it is extremely difficult to set up the Total Station so that is perfectly level. If my partner and I set up the Station so that it was just slightly off balance it would account for the inconsistency of our data. I also mentioned that there were many pedestrians crossing our line of sight as my partner and I were collecting data points. It's also possible that our elevation data was skewed by the interference of these pedestrians with the Total Station's laser.

CONCLUSION

          Overall this was a tough field exercise due to having to work with unfamiliar and complicated equipment. Working with the HiperSR unit in tandem with the Tesla unit was actually a fun experience because they were easy to understand and produced accurate results. Working with the Topcon Total Station was a horse of a different color. The level of effort that goes into setting up a total station is astronomically higher than a HiperSR. Even though my partner and I inputted a lot of effort into the setup, the results of the Total Station elevation data were still highly inaccurate. I stated above that it is good to have a back up system and a broad base of knowledge when it comes to using surveying equipment, but if at all possible I would opt to use the HiperSR GPS unit for any and all surveying applications.

Field Exercise 8 - TruPulse Range Finder Distance Azimuth Survey

INTRODUCTION

          For field exercise eight a partner and I were tasked with measuring and recording a distance azimuth survey. A distance azimuth survey is an older process of surveying where a reference point is used for the basis of the entire survey. Surveyors chose a reference point based on how easy it is to recognize from aerial imagery and measure a desired number of data points out from that reference point. Surveyors measure these data points by picking out objects or landmarks surrounding the reference point and measuring there distance an azimuth in relation to the reference point using a measuring tape and compass. My partner and I measured and recorded 100 data points. My partner and I did not, however, go as old school as using a tape measure and compass. Instead we used a true pulse 200 Range Finder which shoots out a laser to instantly measure both the distance an object is from the reference point and the azimuth of the object. The reason why my partner were instructed to utilize this method of surveying versus something more complex and high tech is that sometimes things may go wrong out in the field and older methods that use fewer technologies may be necessary to get the job done.

Study Area

          My partner and I chose to conduct our survey in a grassy field just West of the UW-Eau Claire McIntyre Library. This area had a good central location in which to place the reference point as well as many surrounding landmarks/objects with which we could measure and record as data points. The image in figure one below shows the location on which we conducted our distance azimuth survey.



Figure 1: shows the lower UW-Eau Claire campus. Inside the red box is the field in which my partner and I conducted our distance azimuth survey.



METHODOLOGY

 

          To get started my partner and I set up the TruPulse Range Finder on a tripod so that it was unable to move its position from start to finish. Then, using a downloaded phone app we took the coordinates of our reference point (middle of the TruPulse Range Finder tripod). collecting the reference points coordinates is not necessary if it's easily identifiable from aerial imagery. We then divided the surveying into two different jobs. Person number one was tasked with actually measuring the data points with the TruPulse. To use the TruPulse Range Finder all a surveyor has to do is turn it on (make sure it has enough battery), toggle between its different functions (two of them are distance in meters and azimuth in degrees), and press a button to shoot the laser at the object of interest. Below in figure two is an image of a TruPulse 200 Range Finder mounted on a tripod.

Figure 2: shows a TruPulse 200 Range Finder mounted on a tripod.

Person number two was tasked with recording the data in a notebook. Person number recorded the distance the data point was away from the reference point in meters, the azimuth the data point was in relation to the reference point in degrees, and what type of object the data point was. Many of the data points were trees but some others included light poles, cars, rocks, and benches. It was important that we recorded data point type because later on when the data points are overlaid onto aerial imagery they will be compared with actual features, and labeling them by type will allow us to know which point is supposed to match up with certain features. After this data was measured and recorded my partner and I inputted it into an excel spread sheet which can be viewed in table one below.

Table 1: shows the distance azimuth data as an excel spread sheet. The object ID, Distance, Azimuth, Type, Latitude, and Longitude of each data point is given.

The data is now ready to be imported into ArcMap. This is done by creating a geodatabase, right clicking it, and importing the data as a table (single). This process can be viewed in figure three below.

Figure 3: shows the pathway to importing the excel file into a geodatabase table.

Once the table is in the geodatabase the Bearing Distance To Line command is used. This process can be viewed in figure four below.

Figure 4: shows how to navigate to the Bearing Distance To Line tool - Data Management tools > Features > Bearing Distance To Line.

Once the Bearing Distance To Line tool has been run an image like the one in figure five below will pop up.

Figure 5: shows the distance and bearing image. The reference point appears at the center of all the lines which are shooting out to the 100 data points collected for the exercise.

After the Bearing Distance To Line tool is used the Feature Vertices to Points tool needs to be utilized in order to add points onto the ends of the lines. Figure six: below shows the pathway to the Feature Vertices to Points tool.

Figure 6: shows the pathway to the Feature Vertices to Points tool - Data Management tools > Features > Feature Vertices to Points. 

After the Feature Vertices to Points tool is used the final step is to lay down a base map so that some imagery can be viewed. This is an important step because the imagery will show how accurate the surveying data was. Figure seven below shows my partner and mine's data compared to actual imagery.

Figure 7: shows the distance azimuth survey map along with aerial imagery. Each red line leaves the reference point according to it's azimuth and each line ends at a teal point according to it's distance.

DISCUSSION

          Figure seven above shows that the data collected by my partner and I was not completely accurate. Three points appear in the building to the northeast of the reference point, and six points appear in the building to the east of the reference point. There are two different theories I have hypothesized that could explain this error the first of which is a bad reference point. My partner and I chose to put our reference point in the middle of the field so that we could have 360 degrees with which to measure data points. In hind sight we should have picked the corner of a building so that we could pin point exactly where our reference point was by looking at aerial imagery. The other theory is that knocking over the tripod halfway through our data collection screwed things up. The wind was gusting up to twenty miles per hour on the day we conducted our survey and it knocked over the tripod at one point. My partner and I had difficulty finding the exact same spot we had set up the tripod so it may have been a few inches off.
          Something I should mention when talking about conducting a survey is magnetic declination which is the angle between magnetic north and true north. Basically the direction a compass points to is magnetic north and the direction along the earth's surface towards the geographic North Pole is true north. The difference between the two is magnetic declination and in Eau Claire's case it is 1.36 degrees west. This means that every azimuth measured needs 1.36 degrees subtracted from it to be accurate. Magnetic Declination is an important concept to understand because it can cause a survey to be inaccurate if it is not accounted for. For my surveys purposes correcting for magnetic declination was not imperative, but if it was a survey being conducted for a high end firm I would have to account for this error.
          Although my partner and I used a relatively new piece of technology (TruPulse 200 Range Finder) to measure both the distance and azimuth of the data points in relation to the reference point, the method is an old one and has been replaced with newer methods such as dynamic surveys, controlled networks surveys, and trilateration surveys. As stated above, there are times when an older method must be fallen back on because of technology failure or budget constraints. Having a backup method that is quick and cost effective is a great plan B.

CONCLUSION

          Being aware of the different types of errors that can occur was the most important part of this field exercise. There was nothing My partner and I could have done about the wind blowing our tripod over, but we definitely should have had the foresight to pick a better reference point. At the very least we were able to overcome the magnetic declination difference between magnetic north and true north. This exercise marked the first time that groups conducted their surveys without collusion with other groups or the instructor. For me it was a defining moment in my geospatial technologies world.