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Model-based constraints for trajectory determination of quad-copters: Design, calibration & merits for direct orientation

Davide Antonio Cucci, Kenneth Joseph Paul, Jan Skaloud

This paper proposes a novel method to improve georeferencing of airborne laser scanning by improved trajectory estimation using Vehicle Dynamic Model. In Vehicle Dynamic Model (VDM), the relationship between the dynamics of the platform and control inputs is used as additional observations for sensor fusion. This relationship is available for most platforms and can be used without the need for additional hardware. However, this relationship is modeled using parameters that are a priori unknown. The proposed in-flight calibration methodology can achieve less than 2% error in the estimated model parameters compared to the values used in simulation. The effect of Inertial Measurement Unit (IMU) noise on the accuracy of airborne laser scanning is further investigated to demonstrate the reduction in the position error of georeferenced points when VDM measurements are used. The results are evaluated through a Monte-Carlo simulation involving an open-source autopilot. The reduction in the error of the estimated attitude due to vehicle modeling increases with the higher intensity of time-correlated IMU noise. Using a higher quality inertial sensor does not lead to an improvement in the position error of georeferenced points when VDM measurements are employed; however, a lower quality Inertial Measurement Unit, such as those on an autopilot, shows a 33% and 46% reduction in the mean and standard deviation of the position error of the georeferenced points, respectively.

2023

Lidar point-to-point correspondences for rigorous registration of kinematic scanning in dynamic networks

Aurélien Arnaud Brun, Davide Antonio Cucci, Jan Skaloud

With the objective of improving the registration of lidar point clouds produced by kinematic scanning systems, we propose a novel trajectory adjustment procedure that leverages on the automated extraction of selected reliable 3D point–to–point correspondences between overlapping point clouds and their joint integration (adjustment) together with raw inertial and GNSS observations. This is performed in a tightly coupled fashion using a dynamic network approach that results in an optimally compensated trajectory through modeling of errors at the sensor, rather than the trajectory, level. The 3D correspondences are formulated as static conditions within the dynamic network and the registered point cloud is generated with significantly higher accuracy based on the corrected trajectory and possibly other parameters determined within the adjustment. We first describe the method for selecting correspondences and how they are inserted into the dynamic network via new observation model while providing an open-source implementation of the solver employed in this work. We then describe the experiments conducted to evaluate the performance of the proposed framework in practical airborne laser scanning scenarios with low-cost MEMS inertial sensors. In the conducted experiments, the method proposed to establish 3D correspondences is effective in determining point–to–point matches across a wide range of geometries such as trees, buildings and cars. Our results demonstrate that the method improves the point cloud registration accuracy (~5x in nominal and ~10x in emulated GNSS outage conditions within the studied cases), which is otherwise strongly affected by errors in the determined platform attitude or position, and possibly determine unknown boresight angles. The proposed methods remain effective even if only a fraction (~0.1%) of the total number of established 3D correspondences are considered in the adjustment.

2022

On the benefit of concurrent adjustment of active and passive optical sensors with GNSS & raw inertial data

Davide Antonio Cucci, Kyriaki Mouzakidou, Jan Skaloud

In airborne laser scanning a high-frequency trajectory solution is typically determined from inertial sensors and employed to directly geo-reference the acquired laser points. When low-cost MEMS inertial sensors are used, such as in lightweight unmanned aerial vehicles, non-negligible errors in the estimated trajectory project to the final point-cloud, resulting in unsatisfactory accuracy on the ground. There are different multi-sensor fusion approaches to correct the point-cloud errors caused by an imperfect trajectory determination. Mismatches between different optical observations and/or in the overlapping regions of the point-cloud can allow the correction of the final point-cloud, either directly, by means of rigid transformations, or indirectly, via improving the scanner trajectory estimation. In this work we propose to fuse lidar and cameras in a single adjustment based on dynamic networks, considering 2D tie-points from the imagery and 3D tie-points from overlapping point-cloud sections. On a challenging corridor mapping scenario, we show that considering either 2D or 3D tie-points, along with inertial and GNSS observations, results in a remarkably accurate point-cloud, even when low-cost inertial sensors are employed and in presence of challenging surface textures, such as high vegetation. Furthermore, since the distribution of the 2D and 3D tie-points is complementary, considering them together further increases the robustness of the adjustment due to higher redundancy. By employing the proposed approach within this controlled example, we were able to improve the final point-cloud accuracy by more than three times with respect to conventional geo-referencing methodology and to reduce the magnitude of the errors.

2022