GMap获取可视范围内四个角的坐标

原理：

先获取控件的四个顶点，逐一将其转换成经纬度坐标。

        private void GetBonds()
        {
            //左上↖
            PointLatLng pLeftTop = map1.FromLocalToLatLng(map1.Left, map1.Top);
            //左下↙
            PointLatLng pLeftDown = map1.FromLocalToLatLng(map1.Left, map1.Top + map1.Height);
            //右上↗
            PointLatLng pRightTop = map1.FromLocalToLatLng(map1.Left + map1.Width, map1.Top);
            //右下↘
            PointLatLng pRightDown = map1.FromLocalToLatLng(map1.Left + map1.Width, map1.Top + map1.Height);

            MapHelper.AddMarker(layMarkers, pLeftTop, Properties.Resources.mark_red_dot);
            MapHelper.AddMarker(layMarkers, pLeftDown, Properties.Resources.mark_red_dot);
            MapHelper.AddMarker(layMarkers, pRightTop, Properties.Resources.mark_red_dot);
            MapHelper.AddMarker(layMarkers, pRightDown, Properties.Resources.mark_red_dot);
        }

　　拖拽完成后执行

        void map1_MouseUp(object sender, MouseEventArgs e)
        {
            if (map1.IsDragging)
            {
                GetBonds();
            }
        }