Assignment 12: Processing UAS Data with GCPs PP

Introduction:

Like the previous assignment, this assignment involves processing imagery using Pix4D. However, this time the imagery will be processed with GCP's. Ground Control Points are an accurately surveyed coordinate location for a physical feature that can be identified on the ground.

Methods:

To begin open Pix4D, and choose New Project. Name the project specifying the date the imagery was collected, your last name, the type of drone used, and lastly add GCP to the end of it. The reason for to be so precise in the name, is to keep things organized and easier to find for later usage. In the edit camera model window, change the shutter model to Linear Rolling Shutter, and add the images labeled UWEC_Topcon in the GCP Manger window shown in Figure 1.

Figure 1. GCP/MTP Manager Window.

Double check the X and Y to make sure they are correct. X should be the Longitude/Eastings, and Y should be the Latitude/Nothings. When you hit OK the GCP's should appear in the flight area. The GCPs will apear as blue crosses, as you can see in Figure 2

Figure 2. GCP's on Imagery.

Once all the GCPs are on the flight area, and in the correct locations, you can start running the initial processing. To prevent issues with the GCP altitudes, and to assure the ray cloud editor works, use the Basic Editor option. Located the GCP marker in two photos for all 16 GCPs, and then reoptimize the project (see Figure 3).   Once the Green X matches the center of the marker you can process the final two steps.

Figure 3. GCP

When the process is completed the Raycloud should look like the one in Figure 4 below.

Figure 4. RayCloud view of imagery

Results/Discussion:

After bringing the data processed imagery into ArcMap, three maps were created. Just like the last assignment, those maps are a Orthomosaic model, a DSM model, and a DSM Hillshade effect, to get the best comparison possible.

Figure 5. Orthomosaic Maps.

For the Orthomoasic Maps in Figure 5, the map with GCPs is smaller and more accurate than the Map without GCPs. The cut out is the same, but as you can see the extent of the image for the map with GCPs is smaller than the extent of the map without GCPs.

Figure 6. DSM Maps.

As you can see in Figure 6, for the DSM map with GCPs, the Elevation is more precise and almost 100 meters higher in elevation than the DSM map without GCPs. THe less color variation means that the GCP map has a smaller range than the map without GCPs.

Figure 7. Hillshade Maps

Figure 7 shows the Hillshade Effect on the DSM imagery, and again you can see how the accuracy of the Z-field has caused a slight change in the elevation. Specifically, the GCP map has less drastic changes than the map without the GCPs.


Conclusion:

In conclusion, there is no doubt that GCP's help to make aerial imagery higher quality and more accurate. The maps with out the GCPs had with a Z-field that was over 100 meters off. In all three maps you can see that the extent of each map is less accurate when there are no GCPs. Outside of the extent change and elevation change, not much is different between the maps.

Sources:

https://support.pix4d.com/hc/en-us/community/posts/206071256-Altitude-Issue-When-Surveying-with-the-DJI-Inspire#gsc.tab=0