When setting up a project using geo-control (only available in PhotoModeler Premium - see Unmanned Aerial Projects), precision values associated with the geo-control tell the algorithms how well the camera station input positions are known. The smaller the precision value the better the positions are known, or the more precise they are.
The default values for Camera Station GPS precision are based on an assumption that the UAV taking the photos was a multi-rotor style UAV with standard GPS and barometric altitude sensor and storage. This generally means that the altitude / height of the UAV is relatively constant - this leads to a small precision value default for Elevation or Z.
The precision values should be different from these defaults in a few cases. Here are some reasonable values for precision in different circumstances.
|
Situation |
Planimetric XY / NE Precision |
Elevation Z Precision |
|
Multi-rotor with standard GPS unit that does not store elevation (automatically detected) |
4.0m |
2.0m |
|
Multi-rotor with standard GPS unit with barometric-based elevation (default) |
4.0m |
0.2m |
|
Multi-rotor with standard GPS unit with GPS based elevation |
4.0m |
4.0m |
|
Fixed wing UAV with standard GPS unit |
4.0m |
6.0m |
|
Fixed wing UAV with standard GPS unit that does not store altitude |
4.0m |
12.0m + |
|
RTK or PPK GPS Unit (see specs from vendor) |
0.05m |
0.1m |
If the vendor gives you the one-sigma precision values for the onboard GPS unit you can use them instead. Note if the input precision values are wrong and don’t match reality (e.g., the Z precision is set to 0.2m but the UAV’s ability to store height values is only precise to 10m) then the processing may not work well. You may not get all photos oriented, or the orientation could be an incorrect shape. Occasionally some experimentation may be required.
The project’s geo-control precision values can be edited using the Global Geo-coordinate Precisions Dialog which can be accessed via the ribbon toolbar’s Create Tab (External Geometry group expand menu), or when prompted during a geocontrol import.