  Registration is a transformation estimation problem between two point clouds,
which has a unique and critical role in numerous computer vision applications.
The developments of optimization-based methods and deep learning methods have
improved registration robustness and efficiency. Recently, the combinations of
optimization-based and deep learning methods have further improved performance.
However, the connections between optimization-based and deep learning methods
are still unclear. Moreover, with the recent development of 3D sensors and 3D
reconstruction techniques, a new research direction emerges to align
cross-source point clouds. This survey conducts a comprehensive survey,
including both same-source and cross-source registration methods, and summarize
the connections between optimization-based and deep learning methods, to
provide further research insight. This survey also builds a new benchmark to
evaluate the state-of-the-art registration algorithms in solving cross-source
challenges. Besides, this survey summarizes the benchmark data sets and
discusses point cloud registration applications across various domains.
Finally, this survey proposes potential research directions in this rapidly
growing field.
