  With the popularity of 3D sensors in self-driving and other robotics
applications, extensive research has focused on designing novel neural network
architectures for accurate 3D point cloud completion. However, unlike in point
cloud classification and reconstruction, the role of adversarial samples in3D
point cloud completion has seldom been explored. In this work, we show that
training with adversarial samples can improve the performance of neural
networks on 3D point cloud completion tasks. We propose a novel approach to
generate adversarial samples that benefit both the performance of clean and
adversarial samples. In contrast to the PGD-k attack, our method generates
adversarial samples that keep the geometric features in clean samples and
contain few outliers. In particular, we use principal directions to constrain
the adversarial perturbations for each input point. The gradient components in
the mean direction of principal directions are taken as adversarial
perturbations. In addition, we also investigate the effect of using the minimum
curvature direction. Besides, we adopt attack strength accumulation and
auxiliary Batch Normalization layers method to speed up the training process
and alleviate the distribution mismatch between clean and adversarial samples.
Experimental results show that training with the adversarial samples crafted by
our method effectively enhances the performance of PCN on the ShapeNet dataset.
