When should I use GCPs vs RTK/PPK?

Choosing between GCPs and RTK/PPK in drone mapping can be tricky, but ultimately, you might benefit from using both for optimal accuracy and project efficiency. Here's a breakdown of why:

GCPs

Advantages

• Sub-inch/Centimeter-level accuracy: Ideal for projects demanding high precision (land surveying, construction, volume calculations).
• Cost-effective for smaller areas: Fewer GCPs needed when also using RTK/PPK.
• Provides ground truth data: Verifies the accuracy of drone-derived coordinates.

Disadvantages

• Time-consuming: Setting up and surveying GCPs takes additional time and effort.
• Not ideal for large areas: Large-scale deployment can be impractical and expensive. Changing site conditions can make the long-term placement of GCPs incredibly difficult.
• Prone to errors: Improper surveying, poor GCP markers, and poor tagging can affect overall accuracy.

RTK/PPK

Advantages

• Real-time or post-processed corrections: Improves accuracy significantly in real-time or during post-processing compared to standard GPS maps.
• Faster data acquisition: No need for setting up or surveying physical points.
• Suitable for large areas: Efficient for covering vast landscapes without GCPs.

Disadvantages

• Lower accuracy than GCPs: Typically a lower level of accuracy in the z-axis.
• Unverifiable accuracy: Without processing checkpoints, RTK/PPK maps cannot be measured for error.
• Can be expensive: Requires specialized equipment and potentially software subscriptions.

Combining GCPs (w/ Checkpoints) and RTK/PPK - Recommended

• Maximizes accuracy: GCPs provide ground truth, while RTK/PPK refines drone-derived coordinates.
• Improves efficiency: GCPs can minimize the dependence on RTK/PPK in critical areas, optimizing data acquisition. Fewer GCPs are needed in combination with RTK/PPK to maximize accuracy.
• Reduces errors: GCPs can identify and mitigate potential inaccuracies in RTK/PPK data.
• Example map:
  • 108 Acre Site flown with the Mavic 3 Enterprise w/ PPK at 200 Feet.
    • 6 GCPs and PPK used to make corrections.
    • 3 Checkpoints placed for validation.
  • Results:

See article: Single GCP Processing for RTK and PPK captures

When to use both

High-precision projects: Land surveying, comparison to modeled data, precise volumetric calculations over time, or for highly accurate as-built data. Use when you need the highest accuracy possible.

Remember: The ideal approach depends on your project requirements, budget, and environmental factors. Consider a cost-benefit analysis and chat with us to determine the best combination for your specific needs.