/// <summary>
/// 找到线圈北侧的点
/// </summary>
/// <returns></returns>
public static List <Vector2d> NourthVertices(this Polygon2d polygon2d)
{
if (polygon2d.IsClockwise) // 为true则是顺时针,
{
polygon2d.Reverse(); // 强制所有线圈为逆时针方向
}
// 1 找到线圈点集的最左、最右，同时偏下的角点
Vector2d leftUpPoint = polygon2d.MaxLeftMaxUpPoint();
Vector2d rightUpPoint = polygon2d.MaxRightMaxUpPoint();
// 2 基于点进行重新排序 排序后便于去点集的区间范围
List <Vector2d> path_Vector2d = polygon2d.ReSortPolygon2dByPoint(rightUpPoint).Vertices.ToList();
int leftUpIndex = path_Vector2d.IndexOf(leftUpPoint);
int rightUpIndex = path_Vector2d.IndexOf(rightUpPoint);
// 所有线圈遵循逆时针模式
int length = leftUpIndex - rightUpIndex + 1;
return(path_Vector2d.GetRange(rightUpIndex, length));
}