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What is the Difference Between GCPs, PPK, and RTK?

Published by Josh Spires on 18 October, 2021, updated on 18 October, 2021.

What is the Difference Between GCPs, PPK, and RTK?

When used in surveying drones are commonly used with one of three technologies, GCPs, PPK, RTK, to improve the GPS accuracy and increase efficiency of aerial surveying. This data is then used to make critical decisions for future projects.

Ground Control Points (GPCs)

Ground Control Points or GPCs have been the go-to method for a while and utilise physical markers on the ground. These markers are then referenced in the post-processing workflow to ensure the accuracy of the data captured.

GPCs are great as they provide accurate and consistent data but take longer to setup and placing the markers down on inaccessible terrain can result less accurate results or being forced to use PPK or RTK.

Post-Processing Kinematic (PPK)

Post-processing kinematic or PPK forgoes the use of physical markers and uses the drone itself and a GNSS base station for improved accuracy. During the flight, the drone will take photos and the position data transmitted from a satellite is then attached to it for use during the post-processing workflow.

As the data is processed after the flight, the GNSS base station doesn't need to be connected to the drone via the controller, allowing the setup to be faster. However, the time needed to process the data afterwards can be substantial, making the time saved negligible.

Real-time Kinematic (RTK)

Real-time Kinematic or RTK is like PPK in the way that it uses a satellite and a base station for its location data however the processing is done in real-time during the flight. RTK requires a little more setup as the base station and controller must be connected but the benefit of not having to process the data after the flight is massive.

RTK hasn't had the best track record as you can't easily go back and fix the data, once it's been captured it often means you will have to do another flight. This isn't as much of an issue now as technology has improved and the connections between the drone and equipment is much more reliable.

Comparison

  Pros Cons
GCPs
  • Trusted and well known.
  • Consistently accurate.
  • Additional time and crew needed for setup.
  • Requires boots on the ground, possibly in hazardous environments.
  • GPS rover and physical targets are required.
RTK
  • Safer: doesn’t require boots on the ground to set up GCPs.
  • Real-time GPS corrections for both the data and the vehicle.
  • No post-processing.
  • Requires digital connection with the base station.
  • No data retention to cross-reference.
  • Loss of link was a cause of malfunctions in the past.
PPK
  • Safer: doesn’t require boots on the ground to set up GCPs.
  • Can eliminate the need for a base station if flying in an area with calibration services.
  • Requires post-processing.
  • Errors introduced in the workflow may compromise project accuracy.
  • Longer workflow timeline to final data product.

Source: Vision Aerial

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