// Return the center of this cell.
public S2Point GetCenter()
{
var ij_size = S2CellId.SizeIJ(Level);
var si = (uint)(2 * ij_lo_[0] + ij_size);
var ti = (uint)(2 * ij_lo_[1] + ij_size);
return(S2.FaceSiTitoXYZ((int)Id.Face(), si, ti).Normalize());
}
public void Test_XYZToFaceSiTi()
{
// Check the conversion of random cells to center points and back.
for (int level = 0; level <= S2.kMaxCellLevel; ++level)
{
for (int i = 0; i < 1000; ++i)
{
S2CellId id = S2Testing.GetRandomCellId(level);
int actual_level = S2.XYZtoFaceSiTi(id.ToPoint(), out var face, out var si, out var ti);
Assert.Equal(level, actual_level);
S2CellId actual_id =
S2CellId.FromFaceIJ(face, (int)(si / 2), (int)(ti / 2)).Parent(level);
Assert.Equal(id, actual_id);
// Now test a point near the cell center but not equal to it.
S2Point p_moved = id.ToPoint() + new S2Point(1e-13, 1e-13, 1e-13);
actual_level = S2.XYZtoFaceSiTi(p_moved, out var face_moved, out var si_moved, out var ti_moved);
Assert.Equal(-1, actual_level);
Assert.Equal(face, face_moved);
Assert.Equal(si, si_moved);
Assert.Equal(ti, ti_moved);
// Finally, test some random (si,ti) values that may be at different
// levels, or not at a valid level at all (for example, si == 0).
int face_random = S2Testing.Random.Uniform(S2CellId.kNumFaces);
uint si_random, ti_random;
uint mask = ~0U << (S2.kMaxCellLevel - level);
do
{
si_random = S2Testing.Random.Rand32() & mask;
ti_random = S2Testing.Random.Rand32() & mask;
} while (si_random > S2.kMaxSiTi || ti_random > S2.kMaxSiTi);
S2Point p_random = S2.FaceSiTitoXYZ(face_random, si_random, ti_random);
actual_level = S2.XYZtoFaceSiTi(p_random, out face, out si, out ti);
if (face != face_random)
{
// The chosen point is on the edge of a top-level face cell.
Assert.Equal(-1, actual_level);
Assert.True(si == 0 || si == S2.kMaxSiTi ||
ti == 0 || ti == S2.kMaxSiTi);
}
else
{
Assert.Equal(si_random, si);
Assert.Equal(ti_random, ti);
if (actual_level >= 0)
{
Assert.Equal(p_random, S2CellId.FromFaceIJ(face, (int)(si / 2), (int)(ti / 2)).Parent(actual_level).ToPoint());
}
}
}
}
}
// Return the vertex where the S2 space-filling curve enters this cell.
public S2Point GetEntryVertex()
{
// The curve enters at the (0,0) vertex unless the axis directions are
// reversed, in which case it enters at the (1,1) vertex.
uint i = (uint)ij_lo_[0];
uint j = (uint)ij_lo_[1];
if ((orientation_ & S2.kInvertMask) != 0)
{
int ij_size = S2CellId.SizeIJ(Level);
i = (uint)(i + ij_size);
j = (uint)(j + ij_size);
}
return(S2.FaceSiTitoXYZ((int)Id.Face(), 2 * i, 2 * j).Normalize());
}
// Return the vertex where the S2 space-filling curve exits this cell.
public S2Point GetExitVertex()
{
// The curve exits at the (1,0) vertex unless the axes are swapped or
// inverted but not both, in which case it exits at the (0,1) vertex.
uint i = (uint)ij_lo_[0];
uint j = (uint)ij_lo_[1];
int ij_size = S2CellId.SizeIJ(Level);
if (orientation_ == 0 || orientation_ == S2.kSwapMask + S2.kInvertMask)
{
i = (uint)(i + ij_size);
}
else
{
j = (uint)(j + ij_size);
}
return(S2.FaceSiTitoXYZ((int)Id.Face(), 2 * i, 2 * j).Normalize());
}
