public override bool IsExisting()
        {
            var points = GetPoints();

            for (int i = 0; i < points.Length; i++)
            {
                var angle = GeometryMath.FindAngle(
                    new LineSegment(points[i], points[(i + 1) % points.Length]),
                    new LineSegment(points[(i + 1) % points.Length], points[(i + 2) % points.Length])
                    );
                if (GeometryMath.IsDoubleEqual(angle, System.Math.PI / 2) == false)
                {
                    return(false);
                }
            }
            return(true);
        }