[CorrespondenceEstimation] There may be something wrong with the annotation about pcl

[mvieth]

Yeah, that might be a bit confusing. CorrespondenceEstimationBase is abstract (so not usable by itself) and the base class/parent class of four non-abstract correspondence estimation methods, including CorrespondenceEstimation. CorrespondenceEstimation is probably the most "basic" or "simple" of the four correspondence estimation methods. See also the inheritance diagram at https://pointclouds.org/documentation/classpcl_1_1registration_1_1_correspondence_estimation_base.html

[QiuYilin]

Then I think modifying this comment would make the meaning clearer. As you said, change it to "CorrespondenceEstimation represents the basic/simple class for determining correspondences between target and query point sets/features". And It would be best if there is also an explanation of the basic principles "For each point in the source point cloud, find the closest point in the target point cloud (usually using KD-tree or other acceleration structures).".