Using GCPs to process data in Pix4D

Assignment Introduction:

This assignment is an overview of processing Pix4D data with Ground Control Points (GCPs). GCPs are a marked point on the ground where you know its true location. This point can then be identified in the image in Pix4D to make sure that your data is accurate. GCPs are not to be confused with check points. Check points only show error but do not correct the data like GCPs do. Figure 1 shows a GCP in the imagery.

Figure 1. Ground Control Point Marking

Assignment Methods:

The first step when processing Pix4D Data is to have correct file structure. This should be done by creating separate folders inside your project folder: Collection, Processing, Analysis. Metadata should also be included in the project folder. Figure 2 shows a proper file convention. 

Figure 2. Correct File Convention

Inside the collection folder should be the imagery and your GCP data. Once you import your imagery data into Pix4D, you should complete the initial processing. This should generate a quality report so you can get an idea of how well your data will process. Figure 3 shows an example of how a quality report should look. 

Figure 3. Quality Report

Once this is done, you will need to use the Raycloud Editor, this will allow you to correct the images to your GCPs. Figure 4 shows what the Raycloud Editor should look like.

Figure 4. Raycloud Editor 

Once your GCPs are corrected you can continue with the DSM and orthomosaic processing. Figure 5 will show the final product after correcting the GCPs

Figure 5. Final Product with GCPs

Assignment Conclusions:

This assignment used GCP corrections, this differs from the previous post where the imagery was processed without GCPs. You can see where the map that used GCPs are a lot more accurate than the map that did not. This is because the corrections were not used to ensure that that data is correct. Figure 6 is the map that was processed with GCPs. Figure 7 shows the map that was processed. Figures 8 and 9 compare the two elevation values, note that the GCP value is a lot more accurate.

Figure 6. Processed Image with GCPs

Figure 7. Processed Image without GCPs

Figure 8. Elevation without GCPs

Figure 9. Elevation with GCPs