With the release of the L1 scanner for the DJI M300 UAV, a paradigm shift has taken place in the UAV scanner market. The RGB color value is assigned to the measuring point as soon as the point cloud is recorded. With a sufficient point density, control point fields can be incorporated more easily into the measurement result and the accuracy can be increased considerably. We have tested the basic accuracy of scanner flights in extensive measurement flights and have come to the conclusion that the Airscanner has advantages in terms of the immediate availability of the measurement results, but the basic accuracy leaves a lot to be desired. Accuracy of less than 10 cm can only be achieved with an appropriate flight arrangement (low flight altitudes) and with visible control point fields and subsequent increased georeferencing.
In comparison to photogrammetric evaluation, one can assume that UAV photogrammetry still delivers better results and higher point densities (at least for normal terrain structures). On the one hand, this is due to the fact that the determined image coordinates are written with great precision in the Exif header. This is at least the case with the PH4 RTK and the M300 from DJI, which determine and enter the eccentricity of the sensor with great precision from distance, direction angle and zenith distance. With the subsequent bundle block adjustment, the image block is determined even without control point fields with an accuracy that is sufficient for many tasks of construction site monitoring, terrain modeling and mass determination. It is still the case here, however, that if you want the cm, you have to go a step further and incorporate an exact control point field into your considerations and calculations according to certain criteria.
