private function rotateY(ball:animation_ch15_Ball3D, angleY:Number):void
    {
     var cosY:Number = Math.cos(angleY);
     var sinY:Number = Math.sin(angleY);
     
     var x1:Number = ball.xpos * cosY - ball.zpos * sinY;
     var z1:Number = ball.zpos * cosY + ball.xpos * sinY;
     
     ball.xpos = x1;
     ball.zpos = z1;
     
     
     if(ball.zpos > -fl)
     {
      var scale:Number = fl / (fl + ball.zpos);
      ball.scaleX = ball.scaleY = scale;
      ball.x = vpX + ball.xpos * scale;
      ball.y = vpY + ball.ypos * scale;
      ball.visible = true;
     }
     else
     {
      ball.visible = false;
     }
    }