There are several reasons that a point cloud or ortho data may not align with checkpoints to the expected accuracy. Below is a list of common reasons that this might occur.
Base station position
In PPK processing, the base station position, antenna height and antenna calibration file must be correct. Please review the Base Station Settings in ASPSuite post regarding the “base station” tab in ASPSuite.
For photogrammetric PPK/RTK processing, it is very important to have a valid camera calibration. Verify that the correct camera calibration is used when processing images to generate a point cloud in Metashape, PIX4D, Context Capture, etc.
Orthometric vs Ellipsoidal elevation
Be sure that the vertical datum and linear units are consistent throughout processing. The desired spatial reference system (SRS), including units, must be used for both PPK/RTK processing output (ASPSuite) and checkpoints. For example, if the checkpoints have a vertical datum of NAVD88 Geoid 12B US Foot, then so must the PPK processing output.
The correct lever arms must be used during PPK/RTK processing. Please review the Lever arm offsets post for more information.
When performing PPK processing, it is important to get a “fixed” solution. Please review the ASPSuite: GNSS Quality Levels Explainedpost for more information.
PPK/RTK processing – updated camera positions, with the correct accuracy level (Example: 0.02 m – fixed) must be used in the photogrammetric processing software (Metashape, PIX4D, Context Capture, etc.)
Control and check points
Control/check point positions need to be accurate. Ensure a suitable methodology was used for creating these points.