Function S2Cell.getEdge

Returns the inward-facing normal of the great circle passing through the edge from vertex k to vertex k+1 (mod 4). The normals returned by GetEdgeRaw are not necessarily unit length. For convenience, the argument is reduced modulo 4 to the range [0..3].

s2.util.math.vector.Vector!(double,3L) getEdge (
  int k
) const;