Introduction-
Lab 6 was focused on the importance of ground control points (GCPs) in digital mapping by remaking lab 5, which had no GCPs, and comparing the difference in accuracy. GCPs are physical points on the area's surface that provide more accurate elevation and photo positioning data. This is important for quality because if GCPs are not used, like in Lab 5, the data collected will still make a DSM, but will not have accurate elevation values. Recording the correct elevation values is important for surveying and designing projects. If elevation is not important for the project, then GCPs are not needed. Check points can be used for this application as well, but not recommended compared to GCPs. This is due to check points will show errors found, but will not adjust to the correct geospatial points required for the most accurate mapping like the capability of GCPs. Figure 1 shows the locations of the GCPs relative to the flight path and data collection points.
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| Figure 1: Initial Image Positions/ GCP locations |
Methods-
The data used in this lab was provided with GCPs and processed in Pix4D to create the DSM. After opening the software, the images provided are to be loaded into the project. Then GCPs are to be added in the GCP/MTP Manager function in the correct fashion being the Y, X, Z coordinate order. After the initial processing, a quality report is provided to display any error found in the project, shown in figure 2. In my processing one image was not used due to a corruption of the photo, shown in figure 3. The GCPs were not correctly aligned with the data collection points, so they needed to be fixed. This portion is a great example as to of why it is important to have accurate and detailed field notes. In this particular case orange arrows were used as GCPs, but exactly where the point is supposed to be was not specified. The correct alignment is at the rear of the point of the orange arrow, and the geolocations of the GCPs are presented in figure 4. Once correctly aligned, the final two process were conducted and produced a final quality report.
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| Figure 2: Initial Processing Details |
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| Figure 3: Calibration Details |
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| Figure 4: Geolocation Details |
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| Figure 5: Quality Report |
Discussion-
Once finished with Pix4D, the project has to be transferred to ArcGIS Pro for final mapping. This project shows great detail of chosen GCPs ], along with another enhanced point near the factory to display the details. The difference between this project and lab 5's project were the use of GCPs. A more concentrated area of the data used in lab 6 was used in lab 5, but the value differences are still relevant. Figure 6 shows the details of the project using GCPs and figure 7 displays lab 5's final map. This comparison is to show how much more accurate the data is using GCPs.
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| Figure 6: Lab 6 Map |
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| Figure 7: Lab 5 Map |
Conclusion-
Developing projects with and without GCPs has shown me that the use of GCPs is accurate and detailed, but can take much more time developing a DSM than without. So the use of GCPs is circumstantial depending on what the final product needs to include. If elevation and very detailed mapping is needed then GCPs are needed, but if a good visual map is needed then not using them will be faster and easier.
