/**
* Convert (face, si, ti) coordinates (see s2.h) to a direction vector (not
* necessarily unit length).
*/
private static S2Point FaceSiTiToXyz(int face, int si, int ti)
{
const double kScale = 1.0 / MaxSize;
var u = S2Projections.StToUv(kScale * si);
var v = S2Projections.StToUv(kScale * ti);
return(S2Projections.FaceUvToXyz(face, u, v));
}
/**
* 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)));
}
// Internal method that does the actual work in the constructors.
private double GetLatitude(int i, int j)
{
var p = S2Projections.FaceUvToXyz(_face, _uv[0][i], _uv[1][j]);
return(Math.Atan2(p.Z, Math.Sqrt(p.X * p.X + p.Y * p.Y)));
}
private double GetLongitude(int i, int j)
{
var p = S2Projections.FaceUvToXyz(_face, _uv[0][i], _uv[1][j]);
return(Math.Atan2(p.Y, p.X));
}
/**
* Return the k-th vertex of the cell (k = 0,1,2,3). Vertices are returned in
* CCW order. The points returned by GetVertexRaw are not necessarily unit
* length.
*/
public S2Point GetVertexRaw(int k)
{
// Vertices are returned in the order SW, SE, NE, NW.
return(S2Projections.FaceUvToXyz(_face, _uv[0][(k >> 1) ^ (k & 1)], _uv[1][k >> 1]));
}
