图形自定义方向拉伸

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对一个二维图形，指定两个垂直方向，依照不同比例进行拉伸。如图

对某一节点到指定基点向量计算推演等式

以基点为原点，将目标坐标系顺时针旋转至直角系，然后进行xy轴向拉伸，再逆时针旋转回去

示例代码（以0、1两点方向为基准方向，0为基准点）

private IGeometry Scale(IGeometry ig){IPointCollection pc = ig as IPointCollection;IPoint bpt = gc.get_Point(0);IPoint npt = gc.get_Point(1);double angle = Math.Atan2(bpt.Y - npt.Y , bpt.X - npt.X);double xff = 2 , yff = 3;//拉伸系数IPointCollection tf = new PolygonClass();double p1 = xff * Math.Cos(angle) * Math.Cos(angle) + yff * Math.Sin(angle) * Math.Sin(angle);double p2 = (xff - yff) * Math.Cos(angle) * Math.Sin(angle) , p3 = p2;double p4 = xff * Math. Sin(angle) * Math. Sin(angle) + yff * Math. Cos(angle) * Math. Cos(angle);For(int i = 0;i<pc.Pointcount;i + + ){IPoint curPt = pc.get_Point(i);double x = curPt.X - bpt.X;double y = curPt.Y - bpt.Y;double dx = x * p1 + y * p3;double dy = x * p2 + y * p4;tf.AddPoint(new PointClass(){X = bpt.X + dx , Y = bpt.Y + dy});        }        return tf as IGeometry;}

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