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With the development of intelligent era, the application of UAVs is more and more extensive, and positioning and navigation technology is the key. Among them, the monocular VIO algorithm, with its advantages of lightweight and low cost, is the research focus of scholars today. However, VIO algorithm based on point features is easy to fail to locate in environments with weak texture, because it cannot extract enough corner features. In this paper, we propose a visual-inertial odometry based on point and line features, which is a tightly-coupled monocular one optimized in real time. In order to improve the positioning accuracy in the low light environments, we propose an image preprocessing algorithm based on adaptive strategy to increase the number of features detected. In order to reduce the difficulty of line feature matching, the method of grouping first and then merging is used to merge the wrongly segmented long line segment features. This also reduces the chasm of line features. At the same time, in the initialization procedure, a least square problem is used to estimate the acceleration bias to improve accuracy in localization. Experiments in the benchmark EuRoc dataset show that under the same operating environments and experimental parameter settings, our algorithm has higher accuracy and better robustness in localization than several mainstream visual-inertial odometry algorithms that only use point features. At the same time, compared with PLF-VINS, IPL-VINS and PL-VINS, the error in localization of our algorithm is reduced by about 0.6%, 18.9% and 9.7%. [ABSTRACT FROM AUTHOR]

The accurate and reliable high-altitude orientation estimation is of great significance for unmanned aerial vehicles (UAVs) localization, and further assists them to conduct some fundamental functions, such as aerial mapping, environmental monitoring, and risk management. However, the traditional orientation estimation is susceptible to electromagnetic interference, high maneuverability, and substantial scale variations. Hence, this paper aims to present a new visual compass algorithm to estimate the orientation of a UAV employing the appearance and geometry structure of the point and line features in the remote sensing images. In this study, a coarse-to-fine feature tracking method is used to locate the matched keypoints precisely. An LK-ZNCC algorithm is proposed to match line segments in real-time. A hierarchical fusion method for point and line features is designed to expand the scope of the usage of this system. Many comparative experiments between this algorithm and others are conducted on a UAV. Experimental results show that the proposed visual compass algorithm is a reliable, precise, and versatile system applicable to other UAV navigation systems, especially when they do not work in particular situations. [ABSTRACT FROM AUTHOR]

The accurate and reliable high-altitude orientation estimation is of great significance for unmanned aerial vehicles (UAVs) localization, and further assists them to conduct some fundamental functions, such as aerial mapping, environmental monitoring, and risk management. However, the traditional orientation estimation is susceptible to electromagnetic interference, high maneuverability, and substantial scale variations. Hence, this paper aims to present a new visual compass algorithm to estimate the orientation of a UAV employing the appearance and geometry structure of the point and line features in the remote sensing images. In this study, a coarse-to-fine feature tracking method is used to locate the matched keypoints precisely. An LK-ZNCC algorithm is proposed to match line segments in real-time. A hierarchical fusion method for point and line features is designed to expand the scope of the usage of this system. Many comparative experiments between this algorithm and others are conducted on a UAV. Experimental results show that the proposed visual compass algorithm is a reliable, precise, and versatile system applicable to other UAV navigation systems, especially when they do not work in particular situations.

The traditional simultaneous localization and mapping (SLAM) system uses static points of the environment as features for real-time localization and mapping. When there are few available point features, the system is difficult to implement. A feasible solution is to introduce line features. In complex scenarios containing rich line segments, the description of line segments is not strongly differentiated, which can lead to incorrect association of line segment data, thus introducing errors into the system and aggravating the cumulative error of the system. To address this problem, a point-line stereo visual SLAM system incorporating semantic invariants is proposed in this paper. This system improves the accuracy of line feature matching by fusing line features with image semantic invariant information. When defining the error function, the semantic invariant is fused with the reprojection error function, and the semantic constraint is applied to reduce the cumulative error of the poses in the long-term tracking process. Experiments on the Office sequence of the TartanAir dataset and the KITTI dataset show that this system improves the matching accuracy of line features and suppresses the cumulative error of the SLAM system to some extent, and the mean relative pose error (RPE) is 1.38 and 0.0593 m, respectively.

High-performance 6D pose estimation and dense 3D mapping with an RGB-D camera has recently attracted substantial research attention since this type of camera can simultaneously capture RGB and depth information. However, there is an unresolved problem in estimating pose and generating highly accurate 3D maps from challenging indoor scenes. This paper presents a real-time simultaneous localization and mapping (SLAM) system based on the RGB-D camera for indoor mobile robots. Our contributions are fourfold. First, we propose a complete high-accuracy SLAM system based on a combination of information from points and lines, which differs from most solutions that rely on only point features. Second, we propose a novel pose solver to handle point and line correspondences, in which a line-based inliers refinement (LBIR) algorithm is proposed to remove outliers. Third, we construct a unified optimization model to concurrently minimize point and line reprojection errors, and extend it to the bundle adjustment (BA) method. Fourth, extensive experiments demonstrate the robustness, accuracy, and real-time performance of the proposed system on public TUM datasets and real world scenes. The empirical results show that the proposed system achieves a comparable or better performance than state-of-the-art methods. Notably, our system can operate in nearly texture-less scenes, while other methods are prone to failure. [ABSTRACT FROM AUTHOR]

Mobile platform visual image sequence inevitably has large areas with various types of weak textures, which affect the acquisition of accurate pose in the subsequent platform moving process. The visual–inertial odometry (VIO) with point features and line features as visual information shows a good performance in weak texture environments, which can solve these problems to a certain extent. However, the extraction and matching of line features are time consuming, and reasonable weights between the point and line features are hard to estimate, which makes it difficult to accurately track the pose of the platform in real time. In order to overcome the deficiency, an improved effective point–line visual–inertial odometry system is proposed in this paper, which makes use of geometric information of line features and combines with pixel correlation coefficient to match the line features. Furthermore, this system uses the Helmert variance component estimation method to adjust weights between point features and line features. Comprehensive experimental results on the two datasets of EuRoc MAV and PennCOSYVIO demonstrate that the point–line visual–inertial odometry system developed in this paper achieved significant improvements in both localization accuracy and efficiency compared with several state-of-the-art VIO systems.

This paper presents a novel approach for estimating the ego-motion of a vehicle in dynamic and unknown environments using tightly-coupled inertial and visual sensors. To improve the accuracy and robustness, we exploit the combination of point and line features to aid navigation. The mathematical framework is based on trifocal geometry among image triplets, which is simple and unified for point and line features. For the fusion algorithm design, we employ the Extended Kalman Filter (EKF) for error state prediction and covariance propagation, and the Sigma Point Kalman Filter (SPKF) for robust measurement updating in the presence of high nonlinearities. The outdoor and indoor experiments show that the combination of point and line features improves the estimation accuracy and robustness compared to the algorithm using point features alone.

Visual simultaneous localization and mapping (SLAM) based on RGB-D data has been extensively researched in the past few years and has many robotic applications. Most of the state-of-the-art approaches assume static environments. However, the static assumption is not usually true in real world environments, dynamic objects can severely degrade the SLAM performance. In order to reduce the influence of dynamic objects on camera pose estimation, this paper proposes an approach that uses static point and line features. Static weights of point and line features indicating the likelihood of features being part of static environment are estimated. According to the calculated static weights, the data associated with dynamic objects are filtered out. The remaining static point and line features are considered inputs for refined pose estimation. Experiments are conducted with challenging dynamic sequences from TUM RGB-D dataset. The results demonstrate that the proposed approach is able to effectively improve the accuracy of RGB-D SLAM in dynamic environments. [ABSTRACT FROM AUTHOR]

To address the problem of estimating camera trajectory and to build a structural three-dimensional (3D) map based on inertial measurements and visual observations, this paper proposes point–line visual–inertial odometry (PL-VIO), a tightly-coupled monocular visual–inertial odometry system exploiting both point and line features. Compared with point features, lines provide significantly more geometrical structure information on the environment. To obtain both computation simplicity and representational compactness of a 3D spatial line, Plücker coordinates and orthonormal representation for the line are employed. To tightly and efficiently fuse the information from inertial measurement units (IMUs) and visual sensors, we optimize the states by minimizing a cost function which combines the pre-integrated IMU error term together with the point and line re-projection error terms in a sliding window optimization framework. The experiments evaluated on public datasets demonstrate that the PL-VIO method that combines point and line features outperforms several state-of-the-art VIO systems which use point features only. [ABSTRACT FROM AUTHOR]

Scan matching, an approach to recover the relative position and orientation of two laser scans, is a very important technique for indoor positioning and indoor modeling. The iterative closest point (ICP) algorithm and its variants are the most well-known techniques for such a problem. However, ICP algorithms rely highly on the initial guess of the relative transformation, which will reduce its power for practical applications. In this paper, an initial-free 2D laser scan matching method based on point and line features is proposed. We carefully design a framework for the detection of point and line feature correspondences. First, distinct feature points are detected based on an extended 1D SIFT, and line features are extracted via a modified Split-and-Merge algorithm. In this stage, we also give an effective strategy for discarding unreliable features. The point and line features are then described by a distance histogram; the pairs achieving best matching scores are accepted as potential correct correspondences. The histogram cluster technique is adapted to filter outliers and provide an accurate initial value of the rigid transformation. We also proposed a new relative pose estimation method that is robust to outliers. We use the lq-norm (0 < q < 1) metric in this approach, in contrast to classic optimization methods whose cost function is based on the l2-norm of residuals. Extensive experiments on real data demonstrate that the proposed method is almost as accurate as ICPs and is initial free. We also show that our scan matching method can be integrated into a simultaneous localization and mapping (SLAM) system for indoor mapping. [ABSTRACT FROM AUTHOR]

The traditional simultaneous localization and mapping (SLAM) system uses static points of the environment as features for real-time localization and mapping. When there are few available point features, the system is difficult to implement. A feasible solution is to introduce line features. In complex scenarios containing rich line segments, the description of line segments is not strongly differentiated, which can lead to incorrect association of line segment data, thus introducing errors into the system and aggravating the cumulative error of the system. To address this problem, a point-line stereo visual SLAM system incorporating semantic invariants is proposed in this paper. This system improves the accuracy of line feature matching by fusing line features with image semantic invariant information. When defining the error function, the semantic invariant is fused with the reprojection error function, and the semantic constraint is applied to reduce the cumulative error of the poses in the long-term tracking process. Experiments on the Office sequence of the TartanAir dataset and the KITTI dataset show that this system improves the matching accuracy of line features and suppresses the cumulative error of the SLAM system to some extent, and the mean relative pose error (RPE) is 1.38 and 0.0593 m, respectively. [ABSTRACT FROM AUTHOR]

Mobile platform visual image sequence inevitably has large areas with various types of weak textures, which affect the acquisition of accurate pose in the subsequent platform moving process. The visual–inertial odometry (VIO) with point features and line features as visual information shows a good performance in weak texture environments, which can solve these problems to a certain extent. However, the extraction and matching of line features are time consuming, and reasonable weights between the point and line features are hard to estimate, which makes it difficult to accurately track the pose of the platform in real time. In order to overcome the deficiency, an improved effective point–line visual–inertial odometry system is proposed in this paper, which makes use of geometric information of line features and combines with pixel correlation coefficient to match the line features. Furthermore, this system uses the Helmert variance component estimation method to adjust weights between point features and line features. Comprehensive experimental results on the two datasets of EuRoc MAV and PennCOSYVIO demonstrate that the point–line visual–inertial odometry system developed in this paper achieved significant improvements in both localization accuracy and efficiency compared with several state-of-the-art VIO systems. [ABSTRACT FROM AUTHOR]

To address the problem of estimating camera trajectory and to build a structural three-dimensional (3D) map based on inertial measurements and visual observations, this paper proposes point-line visual-inertial odometry (PL-VIO), a tightly-coupled monocular visual-inertial odometry system exploiting both point and line features. Compared with point features, lines provide significantly more geometrical structure information on the environment. To obtain both computation simplicity and representational compactness of a 3D spatial line, Plücker coordinates and orthonormal representation for the line are employed. To tightly and efficiently fuse the information from inertial measurement units (IMUs) and visual sensors, we optimize the states by minimizing a cost function which combines the pre-integrated IMU error term together with the point and line re-projection error terms in a sliding window optimization framework. The experiments evaluated on public datasets demonstrate that the PL-VIO method that combines point and line features outperforms several state-of-the-art VIO systems which use point features only.

Scan matching, an approach to recover the relative position and orientation of two laser scans, is a very important technique for indoor positioning and indoor modeling. The iterative closest point (ICP) algorithm and its variants are the most well-known techniques for such a problem. However, ICP algorithms rely highly on the initial guess of the relative transformation, which will reduce its power for practical applications. In this paper, an initial-free 2D laser scan matching method based on point and line features is proposed. We carefully design a framework for the detection of point and line feature correspondences. First, distinct feature points are detected based on an extended 1D SIFT, and line features are extracted via a modified Split-and-Merge algorithm. In this stage, we also give an effective strategy for discarding unreliable features. The point and line features are then described by a distance histogram; the pairs achieving best matching scores are accepted as potential correct correspondences. The histogram cluster technique is adapted to filter outliers and provide an accurate initial value of the rigid transformation. We also proposed a new relative pose estimation method that is robust to outliers. We use the lq-norm (0 < q < 1) metric in this approach, in contrast to classic optimization methods whose cost function is based on the l₂-norm of residuals. Extensive experiments on real data demonstrate that the proposed method is almost as accurate as ICPs and is initial free. We also show that our scan matching method can be integrated into a simultaneous localization and mapping (SLAM) system for indoor mapping.

This paper presents a novel approach for estimating the ego-motion of a vehicle in dynamic and unknown environments using tightly-coupled inertial and visual sensors. To improve the accuracy and robustness, we exploit the combination of point and line features to aid navigation. The mathematical framework is based on trifocal geometry among image triplets, which is simple and unified for point and line features. For the fusion algorithm design, we employ the Extended Kalman Filter (EKF) for error state prediction and covariance propagation, and the Sigma Point Kalman Filter (SPKF) for robust measurement updating in the presence of high nonlinearities. The outdoor and indoor experiments show that the combination of point and line features improves the estimation accuracy and robustness compared to the algorithm using point features alone.