Aerotriangulation

aerotriangulationDAS’s digital production process uses aerial triangulation techniques to combine the short-term accuracy of the IMU with the high global accuracy of GPS. In combination with a minimum number of ground control points, aerial triangulation delivers best fitting results on the ground. The extra information added to the system by automatic tie point measurement (APM) leads to very reliable orientation results where photogrammetric measurements serve to control IMU/GPS measurements and vice versa.

The triangulation process involves automatic measurement of tie points and interactive measurement of control points. Tie points are generated through image correlation techniques using a combination of three stereo model options per flight line: forward/nadir, forward/backward, and nadir/backward. The results of APM are run through a combined bundle adjustment process to further refine the measured image coordinates and the position and attitude values from IMU and GPS computed by IMU/GPS post processing.

aero2The bundle adjustment process equally compensates for systematic errors such as the misalignment between IMU and Camera axes, IMU/GPS drift, and the datum difference between IMU/GPS and the ground control coordinate system. This result is a very accurate and precise determination of the parameters of exterior orientation which are later used for orthorectification.

The DTM/DEM is a key ingredient used in the creation of digital orthophotography. DAS technicians are skilled in the generation and use of DTM/DEM products used to support the production of digital orthophotos.

The raw Level-0 true-color imagery is orthorectified to the DEM using the adjusted position and orientation results from the aerial triangulation phase. The orthorectified strip of imagery is then used in the final orthophotography production process.