Field Activity 9: Surveying with a Total Station

Introduction:

This week the class was to go out and survey the University of Wisconsin-Eau Claire campus mall using a Topcon total station (Figure 1) provided by the geography department.  In Field Activity 4 (Sunday, February 23rd, 2014), the class performed a distance/azimuth survey.  This previously learned method works well in many ways and is quite simple.  However, more accuracy is at times needed, and elevation data is also nice to have.  Surveying using a total station provides these, at times, desired options.  It takes elevation data and is usually more precise than a simple distance/azimuth survey.  This however, comes at a cost.  This cost is both seen in monetary amounts and in convenience.  The total station that was used to complete this activity costs over $4,000.  Also, the set up of the total station is much more complicated than the point and shoot method of the distance/azimuth survey.

This is a total station built by Topcon.  It can be used to more accurately survey an area than a distance/azimuth survey laser and also provides elevation data.  This device can cost upwards of $5,000 and is more complicated to set up than a simple distance/azimuth survey. (Figure 1)

The class spent the in lab period learning how to set up and operate the total station using a GPS that would be connected via Bluetooth to the total station.  The set up involved first learning that the equipment is extremely expensive and should be handled with care, and also that in order for the total station to work, everything needs to be leveled.  Properly leveling off the total station can take some time and involves adjusting the tripod legs and black nobs on the total station itself.  After the station is all leveled, the GPS needs to be activated and connected via Bluetooth.  From here the instructor, Joe Hupy, walked the groups of three through the process of being completely prepared and setting a backsight, which is necessary to collect points and will be further explained in the Methods section.

Each group was to get together and collect their data of the campus mall.  From here the groups would be required to upload the data into ArcMap and create feature surfaces similar to Field Activity 2 using surface interpolation.  These surfaces should ideally mimic the actual campus landscape.


Study Area:

The newly redesigned University of Wisconsin-Eau Claire campus (Figure 2, Figure 3, and Figure 4) was the area in which the survey was performed.  Recent renovations to the campus mall have greatly expanded it.  It is now a large open area which includes Little Niagara Creek as a main feature.  The weather was a pleasant spring temperature and slightly cloudy; as long as it didn't rain the study could have been performed.

This image shows the main portion of the campus mall.  As can be seen the image slopes slightly down in one direction toward Little Niagara Creek on the left.  (Figure 2)

This image shows another view of the campus from the
 total station.  This is facing the newly renovated
 student center and shows the downward slope towards
 Little Niagara Creek.  (Figure 3)

This is a backwards view from Figure 2 above.  It
shows one of the higher flatter areas of campus.  It can
be seen that the campus mall is new by looking at the
freshly planted trees.  (Figure 4)

Methods:

The group obtained all of the needed equipment from the geography lab and set out to the center of campus to begin collecting data.  The total station was set up and leveled off as was shown in the learning session, and the study area was defined.  How the study area was defined is a group member took four flags to place at each corner of the approximate hectare that was to be established.  The hectare was defined by using a pace count (see Field Activity 5) and turning approximately 90 degrees in order to get a square 100 meters.  This wasn't exact as there are parts of campus that are too narrow because of buildings to have an exact 100 meters across.

The group then connected the GPS to the total station and collected an occupy point.  The occupy point is the point directly where the station is placed when it is collecting.  It is taken by simply taking a location using the GPS, in this case the mapping grade GPS took an average of twenty points to calculate the occupy point.  Referencing the occupy point is key in the total station being able to place the points it measures out in space.  From here the group began to set the backsight.

The backsight is required in order to begin taking any points.  A backsight involves taking an azimuth measurement manually and then firing the topcon laser into the total station reflector (Figure 5), which is how points are collected.  This allows the total station to calculate the azimuth of the direction it is facing, which it cannot do without manually setting a backsight.  The azimuth of the backsight was just measured with a compass.  This seems like a simply process, however the group had problems getting the total station to measure out the backsight.  As it turns out, the total station is a delicate machine and needs to have the firing laser faced a certain direction on the station.  Once the laser side of the machine was flipped around, the total station began working exactly as it should.

This is a smaller version of the total station reflector.  The total station needs to be aimed at the center of the prism in order to calculate the distance and azimuth from the total station.  One person walked around holding the rod with this prism on the end level while the other two would aim and fire the total station, recording points.  By knowing the height of the rod and of the total station itself, the total station can calculate elevation. (Figure 5)

Each member of the group rotated either aiming the total station laser at the prism (Figure 6), holding the prism, or manning the GPS as the group was comprised of three members.  A pace count was used to spread out the points in most of the flat areas.  The area by the creek required a more staggered point placing, with points being taken to reflect the real world rapid changes in elevation near the creek (Figure 7).

Here Brielle is insuring the total station is level as she aims it at the reflecting prism.  The other two group members are off to the side either holding the reflecting prism at a desired location or pressing measure on the GPS to gather the points via Bluetooth.  (Figure 6)

This is an image of the points locations after they were uploaded into ArcMap.  These points are correctly spaced, however the satellite imagery is outdated.  The old student center was located where the current campus mall is and where the study took place.  The location of the new student center can be seen in Figure 3 as being across the creek at the bottom of the satellite image.  It can also be seen that as the elevation changed more rapidly near the creek, it was required to take more points to best represent the natural rapid changes in elevation.  From here the points could be run through spatial interpolation to create a surface of the terrain in ArcMap and display it in ArcScene.  The total area of points is approximately a hectare.  (Figure 7)

Approximately 130 points were gathered in total.  After the collection was finished, the equipment was packed up and the points were brought into Excel as a text file.  From there x and y coordinates (using UTM as the data was gathered in UTM zone 15) were converted into a feature with an elevation z.  Spatial interpolation (kriging method) was then run in order to create a surface that represents the terrain of campus (Figure 8).

This is a representation of the campus terrain that was created using the points gathered in the total station survey.  Kriging was used to convert the points into a raster that included elevation data.  the downward slope of the campus mall and the creek are two noticeable aspects of this feature which reflect the real world for the most part.  Some irregularities are the portion of higher elevation in the creek bed caused by a bridge, and the lack of the creek continuing to be represented upstream.  (Figure 8)

The surfaces created from various groups was then compared (Figure 9) to see the various differences in study area and to see if there were any irregularities in any surveys.

These three surfaces of campus were created using three different groups' points.  They were all created using kriging interpolation.  As it can be seen, different groups decided on the approximately hectare-sized area of campus they would survey differently.  However, the change in elevation is reflected similarly in each surface, the stream in the images stands out as a clear feature that each of these groups captured well for the most part.  The different surfaces appeared at different elevation, likely due to the inaccuracy of the z value of the GPS.  (Figure 9)

Discussion:

As the surfaces are observed, there are several things that stand out.  The surfaces created by the different groups for the most part accurately represent the slight downward slope of the campus surface to the creek.  However, in the surface created in Figure 8 the creek appears to be somewhat unnatural as it doesn't continue upstream as it actually does in the real world.  This is likely due to a lack of taking points to the edge of the survey area along the side of the creek.  Next time this survey is done, the groups will need to be sure to take points to the limits of the survey area in a case like this in order to better represent natural features.

A real world feature well represented in the surface in Figure 8 is the area directly surrounding the creek.  The group was sure to take more points along the areas in which the change in elevation was greater to try and ensure that the data would be as accurate as possible.  Due to this it appears that the areas alongside the edge of the creek in Figure 8 are well shown.  However, the creek does have a noticeable irregularity.  There is an area of higher elevation along the creek which appears extremely unnatural.  This is due to a bridge being in that area and the land sloping up to greet the bridge.  The bridge could be better represented if some other method to gather data around it or to represent it was used.  In the surface in Figure 8, the bridge simply appears to be an error, so it's important to mention what it actually is.


Conclusion:

Earlier in the semester, the class used a distance/azimuth survey method to survey an area.  This past week, the class stepped it up a level and used a total station to survey a study area.  The total station, while more complicated to set up and much more sensitive, provides a higher level of precision and also provides elevation data which is extremely useful in many cases.  Through the processes of this lab, the class learned how to properly deploy a total station, gather points, and bring them into a GIS in order to analyze them for accuracy.  This activity also took a large amount of group work and collaborating to make surveying work well.  Thankfully the various groups have gotten good at working together and this greatly aided in making the total station survey run smoothly.