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The existing feature based simultaneously localization and mapping (SLAM) systems such as ORB-SLAM only use sparse keypoints as visual constraints in pose optimization. However, the rich photometric information that may be useful for pose optimization is discarded. In order to improve accuracy, we introduce a novel semi-direct residual into both the front-end and back -end of a stereo visual inertial SLAM system. The semi-direct residual is constructed in triangular sub-image patches formed by local keypoints. It reflects the stable local photometric information between two aligned images. The evaluations on the EuRoC MAV dataset and our indoor parking lot dataset prove that the semi-direct residual is able to improve system accuracy. The results also show that the proposed system achieves highly competitive accuracy, while having better realtime performance than ORB-SLAM3.

The slip angle and attitude are vital for automated driving. In this paper, a systematic inertial measurement unit (IMU)-based vehicle slip angle and attitude estimation method aided by vehicle dynamics is proposed. This method can estimate the slip angle and attitude simultaneously and autonomously. With accurate attitude, the slip angle can be estimated precisely even though the vehicle dynamic model (VDM)-based velocity estimator diverges for a short time. First, the longitudinal velocity, pitch angle, lateral velocity, and roll angle were estimated by two estimators based on VDM considering the lever arm between the IMU and rotation center. When this information was in high fidelity, it was applied to aid the IMU-based slip angle and attitude estimators to eliminate the accumulated error correctly. Since there is a time delay in detecting the abnormal estimation results from VDM-based estimators during critical steering, a novel delay estimation and prediction structure was proposed to avoid the outlier feedback from vehicle dynamics estimators for the IMU-based slip angle and attitude estimators. Finally, the proposed estimation method was validated under large lateral excitation experimental tests including double lane change (DLC) and slalom maneuvers.