Given a connected region and a starting point, return a set of cells at
the given level that cover the region.
Note that this method is *not* faster than the regular GetCovering()
method for most region types, such as S2Cap or S2Polygon, and in fact it
can be much slower when the output consists of a large number of cells.
Currently it can be faster at generating coverings of long narrow regions
such as polylines, but this may change in the future, in which case this
method will most likely be removed.
Given a connected region and a starting point, return a set of cells at the given level that cover the region.
Note that this method is *not* faster than the regular GetCovering() method for most region types, such as S2Cap or S2Polygon, and in fact it can be much slower when the output consists of a large number of cells. Currently it can be faster at generating coverings of long narrow regions such as polylines, but this may change in the future, in which case this method will most likely be removed.