Here is Google's code for doing it: https://code.google.com/p/s2-geometry-library/source/browse/geometry/s2cellid.cc#205 https://code.google.com/p/s2-geometry-

Here is Google's code for doing it: https://code.google.com/p/s2-geometry-library/source/browse/geometry/s2cellid.cc#205 https://code.google.com/p/s2-geometry-library/source/browse/... The lookup table it references is generated up here: https://code.google.com/p/s2-geometry-library/source/browse/geometry/s2cellid.cc#28 https://code.google.com/p/s2-geometry-library/source/browse/...