/**
* Return the leaf cell containing the given point (a direction vector, not
* necessarily unit length).
*/
public static S2CellId FromPoint(S2Point p)
{
var face = S2Projections.XyzToFace(p);
var uv = S2Projections.ValidFaceXyzToUv(face, p);
var i = StToIj(S2Projections.UvToSt(uv.X));
var 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(MaxSize, i));
j = Math.Max(-1, Math.Min(MaxSize, j));
// Find the (s,t) coordinates corresponding to (i,j). At least one
// of these coordinates will be just outside the range [0, 1].
const double kScale = 1.0 / MaxSize;
var s = kScale * ((i << 1) + 1 - MaxSize);
var t = kScale * ((j << 1) + 1 - MaxSize);
// Find the leaf cell coordinates on the adjacent face, and convert
// them to a cell id at the appropriate level.
var p = S2Projections.FaceUvToXyz(face, s, t);
face = S2Projections.XyzToFace(p);
var st = S2Projections.ValidFaceXyzToUv(face, p);
return(FromFaceIj(face, StToIj(st.X), StToIj(st.Y)));
}