Unsupervised Learning of Depth and Ego-Motion from Monocular Video Using 3D Geometric Constraints

TL;DR

This paper introduces an unsupervised method for learning depth and ego-motion from monocular video by enforcing 3D geometric consistency, improving accuracy without needing ground truth data.

Contribution

It proposes a novel 3D geometric consistency loss and an approximate backpropagation algorithm, advancing unsupervised depth and ego-motion estimation from monocular videos.

Findings

Outperforms state-of-the-art in depth and ego-motion estimation

Works effectively on uncalibrated, low-quality videos

Enables training on large, varied datasets without supervision

Abstract

We present a novel approach for unsupervised learning of depth and ego-motion from monocular video. Unsupervised learning removes the need for separate supervisory signals (depth or ego-motion ground truth, or multi-view video). Prior work in unsupervised depth learning uses pixel-wise or gradient-based losses, which only consider pixels in small local neighborhoods. Our main contribution is to explicitly consider the inferred 3D geometry of the scene, enforcing consistency of the estimated 3D point clouds and ego-motion across consecutive frames. This is a challenging task and is solved by a novel (approximate) backpropagation algorithm for aligning 3D structures. We combine this novel 3D-based loss with 2D losses based on photometric quality of frame reconstructions using estimated depth and ego-motion from adjacent frames. We also incorporate validity masks to avoid penalizing areas in which no useful information exists. We test our algorithm on the KITTI dataset and on a video dataset captured on an uncalibrated mobile phone camera. Our proposed approach consistently improves depth estimates on both datasets, and outperforms the state-of-the-art for both depth and ego-motion. Because we only require a simple video, learning depth and ego-motion on large and varied datasets becomes possible. We demonstrate this by training on the low quality uncalibrated video dataset and evaluating on KITTI, ranking among top performing prior methods which are trained on KITTI itself.