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.