/**
* Return the leaf cell containing the given {@link S2Point} (a direction vector, not necessarily
* unit length).
*/
public static S2CellId fromPoint(S2Point p) {
int face = S2Projections.xyzToFace(p);
R2Vector uv = S2Projections.validFaceXyzToUv(face, p);
int i = stToIJ(S2Projections.uvToST(uv.x()));
int j = stToIJ(S2Projections.uvToST(uv.y()));
return fromFaceIJ(face, i, j);
}
/**
* Given (i, j) coordinates that may be out of bounds, normalize them by returning the
* corresponding neighbor cell on an adjacent face.
*/
private static S2CellId fromFaceIJWrap(int face, int i, int j) {
// Convert i and j to the coordinates of a leaf cell just beyond the
// boundary of this face. This prevents 32-bit overflow in the case
// of finding the neighbors of a face cell, and also means that we
// don't need to worry about the distinction between (s,t) and (u,v).
i = Math.max(-1, Math.min(MAX_SIZE, i));
j = Math.max(-1, Math.min(MAX_SIZE, j));
// Find the (s,t) coordinates corresponding to (i,j). At least one
// of these coordinates will be just outside the range [0, 1].
final double kScale = 1.0 / MAX_SIZE;
double s = kScale * ((i << 1) + 1 - MAX_SIZE);
double t = kScale * ((j << 1) + 1 - MAX_SIZE);
// Find the leaf cell coordinates on the adjacent face, and convert
// them to a cell id at the appropriate level.
S2Point p = S2Projections.faceUvToXyz(face, s, t);
face = S2Projections.xyzToFace(p);
R2Vector st = S2Projections.validFaceXyzToUv(face, p);
return fromFaceIJ(face, stToIJ(st.x()), stToIJ(st.y()));
}
