question: public S2LatLng ( S2Point p ) { this ( Math . atan2 ( p . z , Math . sqrt ( p . x * p . x + p . y * p . y ) ) , Math . atan2 ( p . y , p . x ) ) ; }
target:  Convert a point (not necessarily normalized) to an S2LatLng. TODO(dbeaumont): Make this a static factory method (fromPoint() ?).