Performance Analysis of COTS’s Low Cost Integrated Systems for Direct Photogrammetry by UAV
Marco Piras, Paolo Dabove, Vincenzo Di Pietra, Ansar Abdul Jabbar, Politecnico di Torino, Italy
UAV systems are daily used for several civilian application, in particular to collect data even in particular condition as natural hazard mapping and environmental monitoring. There are many commercial solutions (fixed wings and multi-rotors) which offer different performance and payloads, but nowadays a limited number of UAVs are able to fly in real time positioning and to collect raw GNSS data. In fact, there are many application where the differential positioning is fundamental, both in real time or off line. An example is the case of glacier monitoring where is very difficult and dangerous to locate the ground control points (GCP) on the iced surface. In this case, the use of RTK or PPK solution is ideally, because it is only necessary to install few GCPs, saving time and risk.
The limited commercial solutions able to work in RTK are very expensive and not all allow to have the PPK, which is a fundamental requirement to avoid to miss the survey.
In this paper will described the preliminary analyses and results obtained using some COTS’s systems devoted to realize RTK and PPK GNSS positioning on UAV platform. Two of the most famous commercial solutions have been tested: TERSUS and PIKSI MULTI.
In both case, the systems have been tested both on the LAB and on the field, realizing specific tests using a multi-rotors. For each system, many factors have been evaluated, in particular the accuracy, the power consumption, the solution stability, stand alone solution and even the IMU performance (PIKSI MULTI).
Each system has been used with its specific antenna and with a compact one, in order to be installed on the UAV. The reference solution has been realized with a OEM board Novatel installed on board of the UAV and connected to a geodetic compact antenna; the lever arm between antennas has been measured.
Considering TERSUS configuration, the test was carried out to verify also the best initialization strategy to have the fixed solution in RTK and PPK. The RTK has been realized using both a GNSS geodetic receiver (Leica 1200) and another TERSUS receiver configured as Master station with radio link.
Furthermore, the PIKSI system has been tested on similar previous condition, installing the system on the UAV and using as ground master station both a geodetic GNSS receiver and another PIKSI system as master station. In this case, the PIKSI system was directly connected to the internal UAV NAVI control, with purpose to use the telemetry link to receive the differential correction by the ground station.
In this case, internal IMU system has been also tested and analyzed, in order to compare its performance with the attitude solution estimated by the NAVI control system, without considering the coupled solution because not directly available.
Both systems are quite stable and with high performance, in terms of accuracy, precision and TTFF. Even the stand alone solutions are quite stable in the time, which allow to be used for UAV’s navigation. Moreover the IMU solution could be used to have “a priori” solution for direct photogrammetry.