/// <summary>
/// 兩個未相交多邊形合併時，依照邊界線先產出中間空白的多邊形
/// </summary>
/// <param name="line1"></param>
/// <param name="line2"></param>
/// <returns></returns>
public Polygon GetConvexHull(LineString line1, LineString line2)
{
return line1.Union(line2).ConvexHull() as Polygon;
}
