Illinois Drone Photography and Mapping

While having an RTK GPS on your drone can significantly improve the accuracy of the geolocation data collected during aerial surveys, there are still several reasons why using ground control points (GCPs) with Pix4D or similar photogrammetry software is recommended:

1. Accuracy Verification: GCPs serve as reference points with known and accurate coordinates on the ground. They allow you to verify the accuracy of the drone-collected data. This is important because even with RTK GPS, there can still be errors introduced due to atmospheric conditions, satellite signal quality, and other factors.
2. Georeferencing: GCPs help in georeferencing the entire dataset. Georeferencing is the process of aligning your drone imagery with a known coordinate system. While RTK GPS provides accurate positioning for the drone, it doesn’t necessarily mean that the imagery is automatically aligned with the correct geospatial coordinates.
3. Correction of Systematic Errors: Photogrammetry processes can introduce systematic errors, such as distortion in the camera lens, sensor inaccuracies, and others. GCPs can help correct these errors and ensure that your model accurately represents the real-world features.
4. Vertical Accuracy: RTK GPS is generally better at providing accurate horizontal coordinates than vertical coordinates. GCPs can help improve the vertical accuracy of your data, which is crucial for applications like elevation modeling, volume calculations, and flood modeling.
5. Large-Scale Projects: In larger projects or projects with varying topography, the accuracy provided solely by RTK GPS might not be consistent across the entire area. GCPs can provide consistent accuracy throughout the project area.
6. Quality Assurance: GCPs provide a means to assess the quality and accuracy of your final outputs. By comparing the coordinates of the GCPs in your dataset to their known real-world positions, you can identify any discrepancies and make necessary adjustments.
7. Regulatory Requirements: In some industries or jurisdictions, regulatory bodies might require the use of ground control points to validate the accuracy of the data collected by drones.

In summary, while RTK GPS technology significantly improves the accuracy of drone-collected data, ground control points are still essential for validating, correcting, and georeferencing your data accurately. They provide an independent and reliable reference to ensure that the outputs of your photogrammetry software align correctly with the real world.