Creating a Topographic Survey for the UWEC Campus

Topographic Survey

Introduction:

When conducting a survey of points that need absolute accuracy, such as points for construction, a survey grade GPS is used. The goal of this activity was to become familiar with the basics of how one of these systems works and some of the advantages of this tool. Attributes would be collected with millimeter accuracy and placed over an imagery basemap to display the features collected.

Methods:

A Topcon Survey GPS was used to collect points in and around the parking lot to the South of Davies Student Center on the University of Wisconsin Eau Claire campus. Attributes being collected included trees, garbage cans, mailboxes, and light posts. The accuracy of the station can be set up depending on the accuracy needed for the specific point. The tall staff with the beacon on the top seen below in figure one as the black post, is where the point is collected using the tripod design for stability. A point is collected based on an average of points continually taken. Accuracy is increased from "Auto" to "Fix". An auto point is collected by taking an average of 20 points to create the point feature, a fix point is taken from an average of 30 points. Both points are extremely accurate and the degree of error in the auto point taken in figure one is a potential for 3mm of error.

Different groups switched out throughout the period of surveying so that everyone would get hands on experience. The final list of attributes collected where put into an Excel spreadsheet which could then be added into ArcMap by "Add XY Data". The surveyed points appear with a high degree of accuracy on a basemap of the campus.

Figure 1: The Topcon Survey grade GPS was set up to collect attributes including trees, trash bins, mailboxes, and light posts.

Discussion and Conclusion:

The process of actually collecting and setting up this GPS is remarkably simple. It is essentially the same thing as a simple hand help GPS only this system is accurate to the millimeter. From the surveyed points a map of the area behind Davies Center could be created. While this is a simple application for such an advanced tool it is obvious that much more advanced applications could be used and points could be gathered to a high degree of accuracy where it actually meters. The biggest issue for me in this lab cam from the fact that the points collected and placed into an attribute table were in decimal degrees and had a massive amount of issues being projected onto a basemap. I could add the points and the would appear correct based on relative location and orientation in the ArcMap workstation however a basemap could not be projected under the points in the right location. Several attempts were made at reprojecting points and setting coordinate systems and projections yet I could not get the two to agree. This is an issue I have been able to solve before and certainly one I will continue to work on as correcting this is an essential skill. 

Topographic Survey with Total Station

Topographic Survey with a Total Station

Introduction:



The field activity for this week was the creation of a topographic survey of the mall area on the University of Wisconsin Eau Claire campus. The style of survey, the use of a total station, is similar to a test done a couple of weeks ago where the survey was conducted with distance/azimuth methods. The only change is that here, with a totally station, points are far more accurate and a "z" value can be given. The collected points will be placed into ArcMap and displayed using interpolation methods to show the topology. This survey is similar to the "Survey of a Terrain Surface" lab at the beginning of this blog. Only this time a real landscape not a constructed model is being surveyed and points are far more accurate with the total station than collected on the model terrain.

Methods

The station is set up and begins gathering points to millimeter accuracy. The survey grade GPS averages out these points to create an "anchor point" or a point of reference for the rest of the points that will be collected. This is also called a "static point", from the creation of this point the station cannot be touched or collected points will be ruined as the point of reference will have changed. The survey grade GPS by Topcon is seen in figure 1. Points are collected in the similar manner that they are in a Distance/Azimuth survey, the total station is told where dew North is and an azimuth and distance are taken from the static point. The difference is the "z" value addition. This addition is done by shooting a laser from the totally station, figure 4, to a prism pole, figure 2. The prism pole is the receptor of the laser beam and provides the total station with the exact distance the laser travelled to hit that point. The mirror on the prism pole is seen in figure 3The "z" value is collected as the change in height from the total station to the prism pole. The height of the total station off the ground is accounted for and the height of the prism on the prism pole is also accounted for by entering in the height that the pole is raised. Once these two values are taken the difference is recorded as the z value.

Figure 1: This GPS is connected to the total station so that it can record the points collected from the prism pole. Gathered points are added immediately to the display.

Figure 2: In order to ensure an accurate point the prism pole shown here must be level. The prism itself is out of the frame and on top of the pole.

Figure 3: This is the prism itself. The viewfinder in the total station is lined up to the reflective surface and a point is gathered bt bouncing a laser off the mirror. Source: http://www.ebay.com/itm/100-brand-new-mini-prism-with-4-poles-for-offset-0-30-total-stations-/151020419979

Figure 4: The total station. Visible in this picture is also the area of interest with the slope around the Little Niagara Creek visible in the background. The viewfinder is the black circle on the face of the station. It is through this that the station is lined up and the laser shot at the prism.

Results:

The data collected from the total station was put into a text file (figure 5) and could be added into arcscene to create a 3D rendering of the points that were collected. The end product was a 3D image using the TIN interpolation method to display the slopes on either side of the Little Niagara Creek. The final image, figure 6, displays measured heights from the total station in meters. The elevations collected with the station gave a fairly accurate result as the output TIN matches the location surveyed.

Figure 5: The attribute table from arcmap of the collected points for interpolation.

Figure 6: The final 3D image of the area of interest.

Conclusion:

The TIN interpolation method worked for the display of the 3D data though other interpolation methods would likely have worked just as well. The total station was able to collect the height of the measured points down to the hundredth meter, an incredibly accurate way to survey points. Of course there were possible errors such as the total station being bumped, the prism pole moving, and data entry which can always be part of a problem. Overall the end product produced an accurate 3D representation of the study area.

 

 



Distance/Azimuth Survey

Introduction:


The Field Activity for this week was once again upset by the ever changing weather conditions of Wisconsin in the spring. The original plan was to survey tree species in Putnam Park on the University of Wisconsin Eau Claire Campus however a mix of snow, rain, and sleet, changed the activity. The alternative was the collection of tree species points on the campus mall, to the West of Phillips Science Hall as shown in the map inset in figure (figure 8). This study area contained a small stream, walking paths, and several trees planted, of various ages, along the stream area. The area of study can be seen in a photo shown from the perspective of the anchor point for the data in figure 1. The goal of this particular activity was to collect points with a spatial reference without relying on a GPS to take points and specific information on that GPS device. Essentially, if there is a technical difficulty in the field, how can an accurate survey still be conducted.

Figure 1: A view from the anchor point towards Phillips Hall and the trees being collected as points.

Methods:


The survey method employed is called a Distance/Azimuth Survey. To run the survey one point is collected with an exact location. From that point, all other points are simply a reference. In order to transfer the desired points into something with a spatial reference two things are needed, the distance to the point to be collected and the azimuth. Distance was collected in meters using Sonic Combo Pro (figure 2) to shoot a sound wave to a collecting beacon held at breast height on the tree being measured. Azimuth is a attribute collected in degrees using the angle away from 0 degrees, or North, the azimuth is an angle measurement from the anchor point. To collect azimuth a TruPulse 360B(figure 3) was used. Seventeen different trees were surveyed with the following information, distance in meters, azimuth in degrees, circumference at breast height, and species. The location in decimal degrees was collected for the position of the anchor point. Together, the collected attributes provide a location of the tree, and the physical information on the tree provides an idea of size and appearance.
The collected data was transferred into a "Share" Excel file and was then converted into X and Y Data points in ArcMap. The decimal degrees measurement was converted into longitude and latitude for mapping purposes and combined into the attribute table in figure 4. The repeat in points seen in the table will be addressed later. "Bearing distance to line" was the first tool used with the purpose of using distance and azimuth to create lines from the anchor point to the collected tree points, the effects of this tool can be seen figure 5, the ESRI definition for this tool is in figure 6. Then the "feature vertices to points" tool added points onto the end of the lines created, the lines were subtracted and only points remained. The ESRI definition for how this tool functions is in figure 7. This data set had to be checked for spatial reference and was reprojected into the GCS_WGS_1984 projection.
The resulting point feature class was placed onto a basemap of the UWEC campus and a map was created to show results (figure 8). The result is a fairly accurate tree survey.

Figure 2: Held to chest height and shot at a receiver the Sonic Combo Pro collected distance in meters.

Figure 3: The TruPulse 360B could be looked through like a mono-scope and a pulse was sent to what was in the crosshairs to measure distance and azimuth.

Figure 4: An attribute table in ArcMap of collected points.



Figure 5: The resulting lines from the bearing distance to line tool.

Figure 6: The ESRI definition of the Bearing Distance to Line tool.

Figure 7:The ESRI explanation of how points are placed with the Feature Vertices to Points tool.

Discussion:


Distance/Azimuth surveying is not without its difficulties or its errors. In fact is was clear to see how errors could occur quite easily. The rain occurring during surveying could have scattered the laser and sound waves damaging the integrity of distance and degree measurements. The point data is also not perfect, as visible in the resulting map there are some species of trees that appear to be growing inside of Phillips Hall, it seems that the farther away from the survey tools the trees are, the less accurate point collection is. There were also several problems when converting the data from a field notebook to an excel file and into ArcMap. At first points were placed in the ocean and data was in decimal degrees not meters. The problem was that the X and Y fields in the Excel file had been switched and was placing the data in the southern hemisphere. A simple issue to fix once the problem is realized but certainly a good lesson in paying attention to the most basic of geospatial methods. The result was a doubled attribute table as stated earlier, this was able to be ignored as quantity was not measured, just location.

Figure 8: The resulting map from the Distance/Azimuth survey of trees by Phillips Hall.

Conclusion:


This is not a perfectly accurate way to survey anything. It certainly has its errors but it still a reliable way to get relative points onto a map. There would be ways to conduct this survey again to make for less errors and difficulties but it would never be as perfect as a survey grade GPS.
If done again more points would be collected at varying distances from the anchor point to get more variance in accuracy. That data set would then be compared to points collected at the same location with more accurate equipment so that the error margin could be studied.
This field activity was helpful for seeing how there are more than just one way to collect points when technical difficulties arise in the field.