Lab # 6: Processing Pix4D imagery with GCPs

Introduction

This lab was nearly identical to lab #4 except we used GCPs this time around. GCPs are Ground Control Points they are points with known coordinates and are used to create a more accurate map. We use GCPs in the field to accurately pin point important locations that we want to map with the most accuracy possible. GCPs are used to create a georeferenced model that uses global accuracy and helps create a more detailed 3D model when processing in Pix4D.

Methods

In this lab we started by opening lab #4 and inserting Ground Control Points into the existing project. We did this by instering the wolfcreek massaged data and putting it into our Pix4D project.

Figure 1: Finding the GCP Data

After inserting the GCPs we had to go into GCP manager and change some settings. We changed the longitude and latitude from XYZ to YXZ to better coordinate with the data.

Figure 2: GCP Manager and Coordinate Order

We continued to go to Ray Cloud editor which is preferred over basic editor because it is  simply better and has less issues.

Figure 3: Ray Cloud Editor

After we enter Ray Cloud editor we had to line up the GCPs with the corresponding images to get the most accurate GCP and imagery. So for about three pictures on each GCP we would line up the yellow circle on the corner of the checkmark which is the GCP. After you hit apply all of the circles and green X’s should line up with that GCP.

Figure 4: Lining Up GCPs

After lining up all the GCPs we went to “Process” and chose “Rematch and Optimize” which made sure all our data was correct before processing.

Figure 5: Rematch and Optimize

Finally we went to process unchecked box one and checked box two and three and processed the data. After that we got our map data with GCPs and our new quality report. This data can now be put into ArcGIS Pro and a new map can be created with the GCP data.

Figure 6: Processing the Data

The quality report allowed me to see the summary and the basic overview of the processed data.

Figure 7: Summary and Overview of GCP Data

The quality report also displayed the accuracy of my GCPs and how they lined up with the wolf creek imagery that was processed.

Figure 8: GCP Review and Accuracy

Discussion

The GCP map we created in this lab compared to the map of the same data with no GCPs is more accurate and professional looking. The map with GCPs allows you to see the distance between the points and allows you to see in closer detail.

Figure 9: Lab #6 GCP Ortho with Insets

Figure 10: Lab #4 Ortho No GCPs Comparison

As you can see there is a difference in quality and professionalism between the lab #6 orthmosaic and the lab #4 orthmosaic. The GCPs creates a more accurate map and allows you to locate precise points that you want to display to others.

Conclusion

This lab allowed me to learn what GCPs are and what they do. The purpose of these points are to increase the precision of you map and bring it to professional quality. When creating and documenting these GCPs you want to take as many notes as possible and make it easier while processing later. It was useful learning this before I actually go out and record GCPs myself because I can now avoid a potential problem in the future.