/*
* Determine the containing hex in ijk+ coordinates for a 2D cartesian
* coordinate vector (from DGGRID).
*
* @param v The 2D cartesian coordinate vector.
* @param h The ijk+ coordinates of the containing hex.
*/
public static CoordIJK FromHex2d(Vec2d v)
{
var h = new CoordIJK();
double a1, a2;
double x1, x2;
int m1, m2;
double r1, r2;
// quantize into the ij system and then normalize
h.k = 0;
a1 = Math.Abs(v.x);
a2 = Math.Abs(v.y);
// first do a reverse conversion
x2 = a2 / M_SIN60;
x1 = a1 + x2 / 2.0;
// check if we have the center of a hex
m1 = (int)x1;
m2 = (int)x2;
// otherwise round correctly
r1 = x1 - m1;
r2 = x2 - m2;
if (r1 < 0.5)
{
if (r1 < 1.0 / 3.0)
{
if (r2 < (1.0 + r1) / 2.0)
{
h.i = m1;
h.j = m2;
}
else
{
h.i = m1;
h.j = m2 + 1;
}
}
else
{
if (r2 < (1.0 - r1))
{
h.j = m2;
}
else
{
h.j = m2 + 1;
}
if ((1.0 - r1) <= r2 && r2 < (2.0 * r1))
{
h.i = m1 + 1;
}
else
{
h.i = m1;
}
}
}
else
{
if (r1 < 2.0 / 3.0)
{
if (r2 < (1.0 - r1))
{
h.j = m2;
}
else
{
h.j = m2 + 1;
}
if ((2.0 * r1 - 1.0) < r2 && r2 < (1.0 - r1))
{
h.i = m1;
}
else
{
h.i = m1 + 1;
}
}
else
{
if (r2 < (r1 / 2.0))
{
h.i = m1 + 1;
h.j = m2;
}
else
{
h.i = m1 + 1;
h.j = m2 + 1;
}
}
}
// now fold across the axes if necessary
if (v.x < 0.0)
{
if ((h.j % 2) == 0) // even
{
long axisi = h.j / 2;
long diff = h.i - axisi;
h.i = (int)(h.i - 2.0 * diff);
}
else
{
long axisi = (h.j + 1) / 2;
long diff = h.i - axisi;
h.i = (int)(h.i - (2.0 * diff + 1));
}
}
if (v.y < 0.0)
{
h.i = h.i - (2 * h.j + 1) / 2;
h.j = -1 * h.j;
}
h.Normalize();
return(h);
}
public CoordIJK(Vec2d v) => FromHex2d(v);
