GPS Topographic Survey

Introduction:

This weeks lab was to use a dualff frequency GPS to get an accurate point that will be accurate to less than a meter.  This can compare to a smartphone GPS which will be around 10m accurate or a consumer GPS which is within 5m.  It also gives an elevation which can be used to create a continuous surface of the area. The GPS is connected through Bluetooth to a handheld device with the interface on it.  This makes it simple and easy to use in the field.  The important aspect for creating an effective surface area map is to get enough points to cover the areas with high relief and to create a study area that will accurately represent the area being studied.  The sampling method that was used is random sampling.  This means that random points were taken through the area rather than in one of the first labs using a sandbox when systematic sampling was used.

Study Area:

• 29 November 2016
• 40 degrees, Rainy
• Location: In front of Centennial Hall on the University of Wisconsin - Eau Claire campus.  The more detailed location would be tot he south of the circle area with the dancers statue.  

Methods:

Materials

Topcon Tesla Field Controller 

Topcon Hiper SR Positioning Unit

Tripod Stand (With level)

Figure 1: Dual band GPS in the background, and Dr. J Hupy holding the Topcon Tesla Field Controller to collect the first elevation point. 

The Data was collected using a dual frequency GPS which included using the materials above.  The information was Bluetoothed to a handheld which was downloaded to a computer.  Dr. Hupy processed the data and shared a text file.  The text file was then processed in Excel to be able to upload it into ArcMap using the import XY tool.  Then, the data can be used to create continuous surface raster layers using the IDW, Kriging, Natural Neighbor, Spline, and TIN tools.


Results/Discussion

Figure 2: Spline Interpolation of Elevation in a 2D view

Figure 3: IDW Interpolation 

Figure 4: Kriging Interpolation Method

Figure 5: Natural Neighbor interpolation 

Figure 6: TIN interpolation

Figure 7: Spline 3-D Interpolation

Figure 8 IDW 3D Interpolation 

Figure 9 Krigling 3D Interpolation

Figure 10: Natural Neighbor 3D Interpolation

Figure 11 TIN 3D Interpolation

Out of all of the different interpolation methods the most accurate one would be Natural Neighbor.  It really does the best at accurately representing the hill and the amount of relief.  The Krigling interpolation also did a decent job at representing the hill, but it did not do as well of a job at getting the amount of slope on the hill. The IDW interpolation method seemed to have too many holes or low spots in areas that were not actually lower, and the spline interpolation method was wavy and did not really do well with the edge of the slope on the hill.  The TIN did create a good image, but seemed to be edgy.  The 3D version of the IDW seemed to have some weird hills created at the top and some holes at the bottom.  This created a weird landscape that does not represent the surface well.

Conclusion

For making a continuous surface map it is important to collect enough points that would make the interpolation more accurate.  It is also important to accurately set up the GPS Unit, and it is important to have it level and upright.  This will create the most accurate data points.  It is also important to collect enough data points in the region with higher relief to represent the real world.  Using a dual band GPS also will create a more accurate point, but it does take longer than a cellphone or a consumer grade GPS.