A SnapFunction that snaps every vertex to itself. It should be used when vertices do not need to be snapped to a discrete set of locations (such as E7 lat/lngs), or when maximum accuracy is desired.
A SnapFunction that snaps vertices to S2LatLng E5, E6, or E7 coordinates. These coordinates are expressed in degrees multiplied by a power of 10 and then rounded to the nearest integer. For example, in E6 coordinates the point (23.12345651, -45.65432149) would become (23123457, -45654321).
A SnapFunction that snaps vertices to S2CellId centers. This can be useful if you want to encode your geometry compactly using S2Polygon::Encode(), for example. You can snap to the centers of cells at any level.