3-D Scene Flow Estimation on Pseudo-LiDAR: Bridging the Gap on Estimating Point Motion

3-D scene flow characterizes how the points at the current time flow to the next time in the 3-D Euclidean space, which possesses the capacity to infer autonomously the nonrigid motion of all objects in the scene. The previous methods for estimating scene flow from images have limitations, which split the holistic nature of 3-D scene flow by estimating optical flow and disparity separately. Learning 3-D scene flow from point clouds also faces the difficulties of the gap between synthesized and real data and the sparsity of LiDAR point clouds. In this article, the generated dense depth map is utilized to obtain explicit 3-D coordinates, which achieves direct learning of 3-D scene flow from 2-D images. The stability of the predicted scene flow is improved by introducing the dense nature of 2-D pixels into the 3-D space. Outliers in the generated 3-D point cloud are removed by statistical methods to weaken the impact of noisy points on the 3-D scene flow estimation task. Disparity consistency loss is proposed to achieve more effective unsupervised learning of 3-D scene flow. The proposed method of self-supervised learning of 3-D scene flow on real-world images is compared with a variety of methods for learning on the synthesized dataset and learning on LiDAR point clouds. The comparisons of multiple scene flow metrics are shown to demonstrate the effectiveness and superiority of introducing pseudo-LiDAR point cloud to scene flow estimation.