Gmap实现旋转原理以及代码

原理：按下鼠标的时候（开始移动）计算校准值，后续的移动中都减去这个校准值。例如当前旋转角度为10，当前按下鼠标点开始移动的旋转角度为30,那么校准值为30-10=20,意思就是从角度为30这个点开始都要减去20让旋转角度值从10开始，不能跳动。后续的持续按下鼠标右键移动中都使用鼠标Location点的角度减去这个校准值作为新的旋转角度值。
即：bearing=newAngel-step;
下面是实现的一些列事件和方法：
getAngle方法计算某点对于中心点的角度。
按下鼠标时计算当前点和当前角度的差值作为校准值：
移动鼠标事件实现旋转：总是将当前点的角度减去校准值作为新的旋转角度：

//自己注意处理注册事件gMap为我的地图控件：
//gMap.MouseMove += gMap_MouseMove;
//gMap.MouseDoubleClick += gMap_MouseDoubleClick;
//gMap.MouseDown += gMap_MouseDown;
//gMap.MouseUp += gMap_MouseUp;

private static object objForLock__step = new object();
        private double __step = 0;
        private double _step //校准值
        {
            get { lock (objForLock__step) { return __step; } }
            set { lock (objForLock__step) { __step = value; } }
        }

private void gMap_MouseDown(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Right)
            {
                var pCenter = gMap.FromLatLngToLocal(gMap.Position);
                var center = new Point((int)pCenter.X, (int)pCenter.Y);
                _step = getAngle(e.Location, center)-gMap.Bearing;gMap.Cursor = Cursors.Hand;
                debug("gMap_MouseDown:_step=" + _step.ToString());
            }
        }
private void gMap_MouseMove(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Right)
            {
                var pCenter = gMap.FromLatLngToLocal(gMap.Position);
                var center = new Point((int)pCenter.X, (int)pCenter.Y);
                //
                var bearing = gMap.Bearing = (float)(getAngle(e.Location, center) -_step);
                debug("gMap_MouseMove:" + bearing);
            }
        }

/// <summary>
        /// 计算旋转角度的相关函数
        /// </summary>
        /// <param name="nowpoint"></param>
        /// <returns></returns>
        public double getAngle(Point nowpoint, Point CentPoint)
        {
            double length = PointLegth(nowpoint, CentPoint);

            double hudu = Math.Asin(Math.Abs(nowpoint.Y - CentPoint.Y) / length);
            double ag = hudu * 180 / Math.PI;

            if ((CentPoint.X - nowpoint.X) <= 0 && (CentPoint.Y - nowpoint.Y) >= 0)
            {
                ag = 90 - ag;
            }
            else
            {
                if ((CentPoint.X - nowpoint.X) <= 0 && (CentPoint.Y - nowpoint.Y) <= 0)
                {
                    ag = ag + 90;
                }
                else
                {
                    if ((CentPoint.X - nowpoint.X) >= 0 && (CentPoint.Y - nowpoint.Y) <= 0)
                    {
                        ag = 270 - ag;
                    }
                    else
                    {
                        if ((CentPoint.X - nowpoint.X) >= 0 && (CentPoint.Y - nowpoint.Y) >= 0)
                        {
                            ag = ag + 270;
                        }
                    }
                }
            }
            ag -= 235;
            return 360-ag;
        }

        /// <summary>
        /// 计算两点间距离
        /// </summary>
        /// <param name="pa"></param>
        /// <param name="pb"></param>
        /// <returns></returns>
        public double PointLegth(Point pa, Point pb)
        {
            return Math.Sqrt(Math.Pow((pa.X - pb.X), 2) + Math.Pow((pa.Y - pb.Y), 2));
        }