angle method

double angle(
  1. Vector3D o
)

Implementation

double angle(Vector3D o) {
  Vector3D cross = .vec3(
    y*o.z - z*o.y,
    z*o.x - x*o.z,
    x*o.y - y*o.x
  );
  return math.atan2(cross.length, dotProduct(o));
}