S2ClosestPointQueryBase is a templatized class for finding the closest point(s) to a given target. It is not intended to be used directly, but rather to serve as the implementation of various specialized classes with more convenient APIs (such as S2ClosestPointQuery). It is flexible enough so that it can be adapted to compute maximum distances and even potentially Hausdorff distances.
Options that control the set of points returned. Note that by default *all* points are returned, so you will always want to set either the max_points() option or the max_distance() option (or both).