REAL-TIME SLAM FOR THE OFF-ROAD AUTONOMOUS DRIVING

Abstract. In this paper we propose a new SLAM algorithm that is robust to the changing environment of the countryside. The hardware part consists of two separate machine vision cameras, joined in stereo, and can be supplemented with LiDAR, IMU and GPS. We introduce a method that can be used to reliably calculate the position of a vehicle in natural environments. To estimate the pose and produce a three-dimensional reconstruction we use a stereo camera rig, inertial measurement unit and the global positioning system. While solving the problem of visual odometry in outdoor scenes we faced a number of difficulties, arising from high dynamic range, as well as the presence of a large number of "similar elements", such as leaves, grass, trees and etc. Under these conditions, it becomes difficult to match feature points in image sequences. HOG-based methods, such as SIFT, SURF and others often do not obtain good matching due to noise, lack of a sufficient number of gradients, and the presence of identical domains. Using neighborhood-based detectors such as DAISY often allows to identify the correct matches, but using them is worth it too expensive. These methods are very demanding on the computational resources and prone to drift. We needed a method that is less expensive, but at the same time provides sufficient accuracy in the trajectory estimation. Direct methods, such as optical flow calculating or direct image matching allow us to map point-to-point in these conditions with high reliability. They also have disadvantages that can be eliminated by using an IMU and modern algorithms. To improve the quality of the algorithms, we solve the reconstruction problem for several frames using the Levenberg-Marquardt optimization method for bundle adjustment. Each pass optimizes frames that are directly related to the last one, we use two threads that perform partial and full optimization of the entire trajectory using graphs to significantly increase the performance of the method.