private Vector3 GetClosestPoint(Vector3 k)
{
Vector3 vK1 = k - _p1;
float tx = Vector3.Dot(vK1, _v41) / _v41Squared;
float tz = Vector3.Dot(vK1, _v21) / _v21Squared;
tx = ExtMathf.SetBetween(tx, 0, 1);
tz = ExtMathf.SetBetween(tz, 0, 1);
Vector3 closestPoint = tx * _v41 + tz * _v21 + _p1;
return(closestPoint);
}