Lab 5: Topographic Survey and Processing Drone Imagery

Problem/Statement: For this lab, the process of generating a TIN using topographic survey points and using drone imagery to create a 3-D map of the Aletsch Glacier will be addressed. The topographic survey and the 3-D map do not correlate with one another.

Part 1: Generating a TIN

Data Collection: In collecting the data to generate a tin, we took a topographic survey of Eau Claire’s Owen Park using a GPS. Because we used a GPS to obtain data points, we only took data points in the open areas of Owen Park. Places with high tree canopy often interfere with the accuracy of GPS because of satellite interference.

Data Processing: Once we took all our data points at Owen Park, we imported the points into a flash drive, then imported them into an Excel sheet. Once the points were imported into an Excel sheet, we imported the excel sheet into ArcMap. The excel sheet included attributes like the X, Y, and Z coordinates of the data points, so once the data was imported into ArcMap the function Display XY Data was used (figure 1). We used the NAD 1983 HARN Wisconsin CRS Eau Claire County coordinate system to project the points (in feet). Once the points were projected on the map, we used the Create TIN tool based on the points, which yielded the map in figure 2.   

Figure 1. The function "display XY data." 

Results: The results yielded a map in figure 2. As seen by the map, we didn’t capture points for the whole park, just the open spaces. The points for the most part captured the elevations, however their representation as a TIN might make Owen Park seem more mountainous then it is. Triangulation often makes points seem steeper than they are, which is the case with Owen Park’s representation. Despite the inaccurate representation of the park’s more gradual elevation changes, the TIN seems to represent the overall character of the X-Y-Z data points and the park’s elevation, just not the changes in elevation.

Figure 2: TIN of the survey. 

Part 2: Creating a 3-D Map of the Aletsch Glacier

Introduction: Drone imagery can be important for creating 3-D images of hard to access places, like the Aletsch Glacier. In this part of the lab, we used drone imagery to create a 3-D image of the Aletsch Glacier, then calculated the volume of the glacier.

Data Collection: For collecting the data, we downloaded RGB drone images from http://www.sensefly.com/education/datasets under the Aletsch Glacier tab.

Data Processing: Once downloaded, we imported the images into Pix4D to create a 3D map. All the X-Y-Z coordinates were included with the pictures, so importing the coordinates were not necessary. Once the data was imported into Pix4D, we created a 3-D map. 

Results: After 5 ½ hours of processing, the results yielded figure 3, a 3-D map of the Aletsch Glacier. 

Figure 3. Results of the Pix4D processing

Using the calculate volume tool in Pix4D, we digitized the approximate area of the glacier to calculate the volume (figure 4). In calculating the volume, the results yielded a terrain area of 337,555.41 m^2, and a total volume of 1,705,429.06 +- 37821.30 m^3.

Figure 4. Calculating the volume of the glacier. The green lines represent the digitizing of the glacier. 

Discussion: This is the second lab we’ve used Pix4D, and I’m seeing its wide array of applications. In the first lab, we created a historical mosaic of the Eau Claire area, and for this lab we created a 3D model of a glacier using drone imagery.