Introduction
Methods
The camera was set to Shutter Priority to maximize the resolution of the images at high-altitude and 15 MPH flight speed, with a shutter speed of 1/1600 sec. The f-stop was set to f-11 (since the flight was conducted in bright light- otherwise an f-stop of f-3.5 is typically used), and automatic aperture and ISO settings were used as well to ensure quality images were captured. By combining the PPK system and Sony A6000 camera, images were captured at a fixed rate during the flight while also gathering spatial information for each image (the responsibility of the PPK) without the use of ground control points (GCPs). Once the PPK was configured and the camera settings were established, the platform was taken out to the field for collection. Upon setting up the platform and performing pre-flight checks, the Measure Ground Control app was used to plan the mission. Within the app, the pilot in command (PIC) can connect to the transmitter, drone, and establish mission settings. The camera type, flight altitude, overlap/sidelap, and flight plan were established before launch with the estimated time of completion, locations of image capture, and battery levels for the drone and transmitter all displayed within the app. Figures 3 and 4 show the application settings and user interface during flight of a different mission. Once the mission was complete, and data was extracted to a computer in the data lab, the next step was to process the PPK .log file from the flight using EZ Surv post-processing software. This step created the necessary geotags for each image in the form of an excel table. This was used as the spatial correction input for processing the flight images in Pix4D. A new project was created and the folder (directory) containing the flight images was selected. Then, the output events file generated in EZ Surv was brought into Pix4D to geotag the images (Figure 5). Pix4D Mapper Next, the advanced coordinate system was set to "Geoid height above ellipsoid" since the output events file generated in EZ Surv was an ellipsoid model (Figure 6). Since we wanted the program to stitch together all of the images creating an orthomosaic, the "3D Maps" product package was selected (Figure 7) which generated an orthomosaic and digital surface model or "DSM" (see Results). Before initial processing, the initial processing settings were configured to use a "Standard" model (Figure 8). An "Alternative" model was used in a separate process (Figure 9). After initial processing, Pix4D generated a quality report that displayed good initial results, so processing steps 2 and 3 were next. All of the default settings were used for both the standard and alternative processes. The two resulting orthomosaics were generated (see Results). ArcGIS Pro An orthomosaic was generated in ArcGIS Pro with the same data to compare the results and efficiencies of each software. First, a new project was created in ArcGIS Pro and the folder containing flight imagery was navigated to. Then, a New Workspace was created under the Imagery tab of ArcGIS Pro. The workspace was given a name and storage location, then flight images were brought into the workspace along with the geotagged image spreadsheet generated from PPK post processing (Figures 10 - 13).
ResultsDiscussionWithout having done too much other than visually inspecting the results in terms of comparing the accuracy between them, however there are some noticeable differences. The first noticeable difference is in the brilliance of the imagery between the Pix4D products and the ArcGIS Pro product. The range of values for the Pix4D orthos appear greater and the colors really pop. Another noticeable difference is the georectification issues displayed throughout the center and along the eastern portion of figure 15. This is shown in the warping trees and janky stitch lines. Figures 13 and 14 also have these issues, but they appear less intense. One piece of data that was compared objectively between the outputs was the cell size or resolution. Figure 13 has a cell size of 0.02265, figure 14 has a cell size of 0.02268, and figure 15 has a cell size of 0.02038. Surprisingly, the ArcGIS Pro model has the best resolution of the three. ConclusionWhile both software produce high quality orthomosaic products, a few lessons were learned from this experiment: 1) Standard calibration in Pix4D produced a better resolution than alternative calibration, 2) ArcGIS produced a better orthomosaic than Pix4D in terms of resolution 3) Pix4D does a better job of georectifying images. So depending on whether the user wishes to preserve resolution for calculations or would prefer a better looking image for more simplistic analyses, the appropriate software should be selected.
0 Comments
Leave a Reply. |
Zach MillerWelcome to my field blog! Here you will find the latest updates on what geospatial projects I'm working on. I also provide in-depth workflows and explainations of how I use different functions in various GIS and UAS software to create deliverables. Have a look around by using the categories side bar or just scroll through. ArchivesCategories |