/// <summary>
/// Determines the H3 digit corresponding to a unit vector in ijk coordinates.
/// </summary>
/// <param name="ijk">The ijk coordinates; must be a unit vector.</param>
/// <returns>
/// The H3 digit (0-6) corresponding to the ijk unit vector, or
/// <see cref="Direction.INVALID_DIGIT"/> INVALID_DIGIT on failure
/// </returns>
/// <!--
/// coordijk.c
/// Direction _unitIjkToDigit
/// -->
internal static Direction ToDirection(this CoordIjk ijk)
{
var c = ijk.Normalized();
var test = Constants.CoordIjk.UnitVectors.Where(pair => pair.Value == c).ToList();
return(test.Any()
? test.First().Key
: Direction.INVALID_DIGIT);
}
/// <summary>
/// Determine the containing hex in ijk+ coordinates for a 2D cartesian
/// coordinate vector (from <a href="http://www.discreteglobalgrids.org/software/">DGGRID</a>).
/// </summary>
/// <param name="v">The 2D cartesian coordinate vector.</param>
/// <!--
/// coordijk.c
/// void _hex2dToCoordIJK
/// -->
public static CoordIjk ToCoordIjk(this Vec2d v)
{
var h = new CoordIjk();
// quantize into the ij system and then normalize
decimal a1 = Math.Abs(v.X);
decimal a2 = Math.Abs(v.Y);
// first do a reverse conversion
decimal x2 = a2 / Constants.H3.M_SIN60;
decimal x1 = a1 + x2 / 2.0m;
// check if we have the center of a hex
var m1 = (int)x1;
var m2 = (int)x2;
// otherwise round correctly
decimal r1 = x1 - m1;
decimal r2 = x2 - m2;
if (r1 < 0.5m)
{
if (r1 < 1.0m / 3.0m)
{
h = r2 < (1.0m + r1) / 2.0m
? h.SetIJ(m1, m2)
: h.SetIJ(m1, m2 + 1);
}
else
{
h = r2 < (1.0m - r1)
? h.SetJ(m2)
: h.SetJ(m2 + 1);
h = (1.0m - r1) <= r2 && r2 < (2.0m * r1)
? h.SetI(m1 + 1)
: h.SetI(m1);
}
}
else
{
if (r1 < 2.0m / 3.0m)
{
h = r2 < (1.0m - r1)
? h.SetJ(m2)
: h.SetJ(m2 + 1);
h = (2.0m * r1 - 1.0m) < r2 && r2 < (1.0m - r1)
? h.SetI(m1)
: h.SetI(m1 + 1);
}
else
{
h = r2 < (r1 / 2.0m)
? h.SetIJ(m1 + 1, m2)
: h.SetIJ(m1 + 1, m2 + 1);
}
}
// now fold across the axes if necessary
if (v.X < 0.0m)
{
if (h.J % 2 == 0) // even
{
long axisI = (long)h.J / 2;
long diff = h.I - axisI;
h = h.SetI(h.I - (int)(2.0 * diff));
}
else
{
long axisI = (long)(h.J + 1) / 2;
long diff = h.I - axisI;
h = h.SetI(h.I - (int)(2.0 * diff + 1));
}
}
if (v.Y < 0.0m)
{
h = h.SetIJ(h.I - (2 * h.J + 1) / 2, -h.J);
}
return(h.Normalized());
}