Topographic Survey

Introduction

This weeks assignment focused on using a survey grade GPS to take elevation data from specific areas on campus. The data was taken from a small patch of grass located in the Campus Mall. The study area was surveyed because the land was rather uneven and it would give the class a chance to utilize the high powered GPS to create digital elevation models. 

Methods

This assignment required the class to make a trip outside to collect some data. The overall study area was small. A small patch of grass located in the campus mall was used as the study area. The class used a high precision, survey grade GPS. The GPS unit was used by every individual in the class. This means that there were roughly 20 points taken to create a DEM. The survey method used was a random sample. This means that the GPS unit was moved to random areas throughout the study area to make sure that all of the points were not being taken from the top of the hill area or at the bottom of the hill. The GPS unit collected both Latitude and Longitude as well as an elevation value.

Once each student got a chance to use the GPS to survey a point, the data was transferred from the GPS to a text file. The data was then imported into an excel spreadsheet from the text file. Once there was a working spreadsheet, it was time to create a file geodatabase. With the file geodatabase, the excel spreadsheet data could be imported and used to create the DEM. This was done by importing the spreadsheet and creating a point feature class. Using the point feature class, different tools could be run to create different DEMs. An IDW, Kriging, Natural Neighbor, Spline, and TIN were all created from the points. All of these DEMs were created in WGS 1984 UTM zone 15 projection so that there is minimal distortion. With these rasters, maps were created to show the elevation changes in the study area. To finish off, these rasters were placed into ArcScene to create 3D images of the rasters to better show the elevation changes. 

Results

The results of this project include all of the different raster DEMs created as well as the different 3D images created. It is interesting to look at how the different interpolation methods change how the data is interpreted. Figure 1 shows the final rasters created in ArcMap.

Figure 1. This is the compilation of all of the rasters that were created in this assignment using different interpolation methods.

Figure 2 through 6 show how all of the different interpolation methods are different through the 3D image creation of ArcScene. 

Figure 2 shows the Kriging interpolation method displayed in ArcScene.

Figure 3 shows the Nearest Neighbor interpolation method displayed in ArcScene.

Figure 4 shows the Spline interpolation method displayed in ArcScene.

Figure 5 shows the TIN displayed in ArcScene. 

Figure 6 shows the IDW interpolation method displayed in ArcScene. 

From looking at these different interpolation methods, you can see which methods worked well for this project. Seeing as there was one larger hill on the Southern side of the raster, the method that truly best displays it is the Nearest Neighbor method. The TIN and Kriging also represent this fairly well. The issues that arise with the IDW and the spline are that you can see specific holes and mounds that do not actually exist in the area.

Conclusion

This project gave the class the opportunity to work with a high precision, survey grade GPS in order to create multiple DEMs to represent a small area on campus. This was a nice project to get to work with the survey grade GPS because we were surveying such a small area that it was very easy to visualize what the DEMs should come out looking like. It was interesting to see how different interpolation methods can change the output by so much. For example, the IDW ended up looking like a completely different area. Overall, this was a very good assignment to teach us how the survey grad GPS works and how to use it as well as refine our skills in creating DEMs using different interpolation methods and being able to interpret them.