Re-size DrawingVisual after rotation.

I am facing issue in calculating the center of the DrawingVisual when it is already rotated, and resized.

I am doing one tool which allows drawing of various shapes in the canvas.

I created a Shape class which derives from  DrawingVisual and rectange class from the shape.

GraphicsRectangle--> GraphicsShape --> GraphicsBase-> DrawingVisual 

Did the rotation related code in the GraphicsShape.

And GraphicsBase is the abstract like class with has some basic function with required for my appln. GraphicsRectangle has code related to resize of rectangle.

I am using GroupTransform for translation and rotation, and set the GroupTransform  object to the DrawingVisual.Transform

I am facing problem in finding the center of the DrawingVisual during the following step.

1. rotate the object to some angle. (say 45)

2. Resize the object.

3. Again rotate. <problem in recalculation of center for rotation tansform>

Every time when i rotate i calculate the center for rotation. Calculation on the center gives a wrong value only when i re-sized object and object shifts to some other place and start rotating.

                                                                                                  

public abstract class GraphicsShape : GraphicsBase
    {

        protected virtual Point GetCenter()
        {
            Rect rect = this.GetBounds();

            var r = this.TransformGroup.TransformBounds(rect);
            Point p1 = new Point(r.Left, r.Top);
            Point p2 = new Point(r.Right, r.Bottom);

            Point c = new Point((p1.X + p2.X) / 2, (p1.Y + p2.Y) / 2);

            return c;
        }
       public virtual void StartMove(Point startPoint, int handleNumber)
        {

            this.centerPoint = GetCenter();
           

            this.startVector = Point.Subtract(startPoint, this.centerPoint);

            


            this.initialAngle = this.rotateTransform.Angle % 360;

            Rect r = this.GetBounds();
            Point p1 = new Point(Math.Min(r.Left, r.Right), Math.Min(r.Top, r.Bottom));
            Point p2 = new Point(Math.Max(r.Left, r.Right), Math.Max(r.Top, r.Bottom));

            Point c = new Point((p1.X + p2.X) / 2, (p1.Y + p2.Y) / 2);
            if (SizeChanged)
            {
                SizeChanged = false;
            }
            this.rotateTransform.CenterX = c.X;
            this.rotateTransform.CenterY = c.Y;
            Console.WriteLine("Start()-Angle: " + this.rotateTransform.Angle);
        }
 private void Delta(Point currentPoint)
        {

            Vector deltaVector = Point.Subtract(currentPoint, this.centerPoint);

            double angle = Vector.AngleBetween(this.startVector, deltaVector);



            this.rotateTransform.Angle = (this.initialAngle + Math.Round(angle, 0));//;% 360.0;

            Console.WriteLine("Delta()-Angle: " + angle + string.Format("     Center: {0} SV: {1} EV: {2}", centerPoint, startVector, deltaVector));

            
        }
  protected override void DoMoveHandleTo(System.Windows.Point point, int handleNumber)
        {
            if (canRotate && RotateHandle == handleNumber)
            {
                    Delta(point);
            }
        }
}

StartMove will be called when i start rotating, Delta will be called for every rotate after start move.

In  start move i am calculating center every time when i start rotating. 

     

class GraphicsRectangle
{

                  
protected override void DoMoveHandleTo(Point point, int handleNumber)
        {
            var inverseP = this.TransformGroup.Inverse.Transform(point);
            switch (handleNumber)
            {
                case 1:
                    rectangleLeft = inverseP.X;
                    rectangleTop = inverseP.Y;
                    break;
                case 2:
                    rectangleTop = inverseP.Y;
                    break;
                case 3:
                    rectangleRight = inverseP.X;
                    rectangleTop = inverseP.Y;
                    break;
                case 4:
                    rectangleRight = inverseP.X;
                    break;
                case 5:
                    rectangleRight = inverseP.X;
                    rectangleBottom = inverseP.Y;
                    break;
                case 6:
                    rectangleBottom = inverseP.Y;
                    break;
                case 7:
                    rectangleLeft = inverseP.X;
                    rectangleBottom = inverseP.Y;
                    break;
                case 8:
                  //  this.rotateTransform.CenterX += this.rotateTransform.CenterY - (rectangleLeft - inverseP.X) / 2;
                    rectangleLeft = inverseP.X;

                    break;
                case int.MaxValue:
                    base.DoMoveHandleTo(point, handleNumber);
                    break;
            }
            if (handleNumber > 0 && handleNumber <= 8 && (this.rotateTransform.Angle%360)!=0)
            {
                SizeChanged = true;
            }
            RefreshDrawing();
        }

}

This is my rectange resize code

Please anyone provide me solution. when i combine Resize after Roation only problem coming. Translation of the object working fine.