Learning by Restoring Broken 3D Geometry

The key point for an experienced craftsman to repair broken objects effectively is that he must know about them deeply. Similarly, we believe that a model can capture rich geometry information from a shape/scene and generate discriminative representations if it is able to find distorted parts of shapes/scenes and restore them. Inspired by this observation, we propose a novel self-supervised 3D learning paradigm named learning by restoring broken shapes/scenes (collectively called 3D geometry). We first develop a destroy-method cluster, from which we sample methods to break some local parts of an object. Then the destroyed object and the normal object are both sent into a point cloud network to get representations, which are employed to segment points that belong to distorted parts and further reconstruct/restore them to normal. To perform better in these two associated pretext tasks, the model is constrained to capture useful object features, such as rich geometric and contextual information. The object representations learned by this self-supervised paradigm transfer well to different datasets and perform well on downstream classification, segmentation and detection tasks. Experimental results on shape datasets and scene datasets demonstrate that our method achieves state-of-the-art performance among unsupervised methods. We also show experimentally that pre-training with our framework significantly boosts the performance of supervised models.