RTK and PPK are GNSS correction methods in photogrammetry; RTK applies real-time corrections, while PPK processes them afterward for greater flexibility. This article explains the recommended workflow when processing such datasets in PIX4Dmatic.
Description
RTK (Real-Time Kinematic)
RTK is a GNSS correction method that provides real-time positioning accuracy by receiving corrections from a base station or a network. It continuously adjusts the camera positions as images are captured, ensuring high-precision geotags. This method requires a stable communication between the rover (camera system) and the base station. RTK is ideal for projects requiring immediate accuracy but can be affected by signal loss in areas with obstructions. Some of the advantages of the RTK approach:
- Eliminates the need to place GCPs in hard-to-reach areas.
- Removes the requirement for GNSS post-processing after the flight.
- Enables real-time corrections using the drone’s GPS positioning, improving waypoint navigation and autonomous landing.
- No post-processing software is needed for real-time operation.
PPK (Post-Processed Kinematic)
PPK applies GNSS corrections after data collection by comparing raw satellite data from the rover and base station. Since corrections are processed post-flight, PPK is more resilient to signal interruptions and does not require a constant connection during image capture. This method is often preferred in challenging environments, such as dense urban areas or forests. PPK provides high accuracy and flexibility, making it a reliable choice when real-time corrections are not feasible. Some of the advantages of the PPK approach:
- No need for GCPs placement and measurement in hard-to-reach areas, reducing setup time and costs.
- Increased data reliability without relying on a constant real-time connection.
- Greater flexibility in challenging environments, with retained GNSS data for accountability and reprocessing.
- Accurate GNSS positioning after the flight, with options for GPS-only or GPS/IMU processing.
RTK workflow
For RTK-enabled datasets, it is highly recommended to follow the workflow described below:
- Import the images in PIX4Dmatic.
- In the Calibration processing step, select the Trusted location and orientation pipeline. This calibration pipeline is intended for projects with accurate relative location and IMU data, such as datasets from RTK drones or devices. All images must include information about the camera's initial position and orientation.
- Continue with the rest of the processing steps according to the project requirements.
RTK and GCPs
For an RTK workflow that maintains a stable correction source, the use of GCPs may not be required. However, using a few GCPs as checkpoints remains the best practice to verify and ensure accuracy.
PPK workflow
For PPK workflows, it is highly recommended to follow the steps described below:
- Import the images in PIX4Dmatic.
- Since the PPK workflow applies post-processing GNSS correction, a .csv or .txt file should be available. Ensure that the .csv or .txt file follows the format described in detail here:
Image location and orientation format - PIX4Dmatic. - Import the image geolocation and orientation file in the PIX4Dmatic project.
- Similar to the RTK approach, select the Trusted location and orientation pipeline in the Calibration processing step. This calibration pipeline is intended for projects with accurate relative location and IMU data, such as PPK datasets with accurate relative location and IMU data in an external file (.csv/.txt).
- Continue with the rest of the processing steps according to the project needs.
PPK and GCPs
For a well-executed PPK workflow with a stable GNSS setup, GCPs may not be required. However, using a few GCPs as checkpoints is still the best practice to verify accuracy and ensure confidence in the results.