DiffCD: A Symmetric Differentiable Chamfer Distance for Neural Implicit Surface Fitting

Fitting neural implicit surfaces to point clouds is typically done by encouraging the network output to equal zero on the point cloud. Yet, since the underlying shape metric is not symmetric, previous methods are susceptible to spurious surfaces. We theoretically analyze the predominant approach for dealing with spurious surfaces, and show that it is equivalent to regularizing the surface area, leading to over-smoothing. To address these shortcomings, we propose a novel loss function corresponding to the symmetric Chamfer distance. It assures both that that the points are near the surface and that the surface is near the points. Our approach reliably recovers a high level of shape detail and eliminates spurious surfaces without the need for additional regularization. To make our approach more practical, we further propose an efficient method for uniformly sampling point batches from the implicit surface. The full implementation of our method and experiments is provided in the supplemental material and will be publicly released upon acceptance.