Overview
Ground Control Points (GCPs) and Checkpoints are essential for ensuring the spatial accuracy of your drone maps. This guide explains how to effectively use these points to anchor your data to the real world and verify the precision of your results.
What are GCPs and Checkpoints?
Ground Control Points (GCPs): Points on the ground with known coordinates that the processing engine uses to geo-reference your map accurately.
Checkpoints: Points used to verify the accuracy of the map after processing. Unlike GCPs, Checkpoints do not influence the processing of the map; they provide an unbiased measurement of its precision.
Distribution best practices
To achieve the highest level of accuracy, follow these distribution guidelines:
A minimum of 4 GCPs is required for non RTK/PPK maps (See more about our Single GCP Processing for RTK and PPK data here.)
Spread points evenly: Place GCPs across the entire project area rather than clustering them in one spot.
Capture the perimeter: Place points near the corners and edges of your flight area to prevent "warping" at the boundaries of the map.
Account for elevation: If your site has significant terrain changes, place points at both the highest and lowest elevations.
Setting up GCPs in DroneDeploy
Follow these steps to incorporate GCPs into your workflow:
Navigate to the Map tab in your project dashboard.
Click Upload and select your imagery.
Select GPS & GCPs from the sidebar menu.
Upload your GCP file: Ensure your file is in a supported format like CSV.
Tag your points: Match the known coordinates to the visual markers in your photos.
Bonus Tips
- Consistency is key: Using the same methods throughout eliminates variables that could introduce errors and compromise accuracy.
- High-resolution camera: More detail means better identification of GCPs and surrounding features, leading to more precise measurements.
- What CRS are we in: Ensuring you know which Coordinate Reference System the GCPs are surveyed in ensures a seamless process when uploading your data.
- Strategic GCP placement includes:
- Surface type: GCP's are best placed on improved surfaces (asphalt, concrete, packed earth, etc) on surface-level ground. GCP's placed on uneven surfaces, such as grass, may impact accuracy.
- Surrounding environment: GCPs should be placed in open, unobstructed areas, away from shadows, vehicles, and vegetation.
- Immobile: GCP's should be placed on a permanent surface between captures. Relocating GCP's creates inconsistency that can impact accuracy.
Remember: GCPs are the bridge between your drone imagery and accurate, real-world measurements. By understanding the reasoning behind these best practices, you can make informed choices that optimize your drone mapping projects for exceptional precision and reliability.
Placement examples:
Limitations and considerations
Visibility: Ensure markers are large enough to be seen clearly in your drone photos. Need a GCP stencil? Check out this link!
Obstructions: Avoid placing points under trees, near tall buildings or under power lines that may block the drone's view or interfere with GPS signals.
Coordinate Systems: Verify that your GCP coordinates use the same coordinate system selected in your DroneDeploy project settings.
FAQs
Q: Does DroneDeploy support RTK/PPK workflows without GCPs?
A: Yes. While RTK and PPK provide high accuracy, we still recommend using at least 1-2 Checkpoints to verify the global accuracy of your data.
Q: Can I change a GCP to a Checkpoint after uploading?
A: Yes. You can toggle the point type within the GCP Management tool before you start processing.
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