C# Gmap.net控件的使用

1，首先要先添加引用Gmap.net的动态链接库.dll文件

2，初始化地图信息

     public void MapShow()
        {

            try
            {
                System.Net.IPHostEntry ela = System.Net.Dns.GetHostEntry("www.google.com.hk");
            }
            catch
            {
                gMap_control.Manager.Mode = AccessMode.ServerAndCache;
                MessageBox.Show("No internet connection avaible, going to CacheOnly mode.",
                                "GMap.NET Demo", MessageBoxButtons.OK, MessageBoxIcon.Warning);
            }

            gMap_control.CacheLocation = Environment.CurrentDirectory + "\\GMapCache\\"; //缓存位置
            MyInvoke my = new MyInvoke(Init);
            this.BeginInvoke(my);
        }

     public delegate void MyInvoke();
        public void Init()
        {


            gMap_control.MinZoom = 4;  //最小比例
            gMap_control.MaxZoom = 22; //最大比例
            gMap_control.Zoom = 4;
            gMap_control.DragButton = System.Windows.Forms.MouseButtons.Left; //左键拖拽地图

            gMap_control.Position = new PointLatLng(32.064, 118.704); //地图中心位置：南京

        }

    gMap_control.MapProvider = GMapProviders.GoogleChinaMap; //google china 地图
        new Thread(MapShow).Start();

3，添加一个market

     GMapOverlay MyMarkss = new GMapOverlay(this.gMap_control, "MyMarkss");
        GMapMarkerGoogleGreen gn = new GMapMarkerGoogleGreen(gMap_control.Position);
        MyMarkss.Markers.Add(gn);

        this.gMap_control.Overlays.Add(MyMarkss);
        gn.ToolTipMode = MarkerTooltipMode.Always;
        gn.ToolTipText = "提示信息"

4，添加一个自定义的market

class GMapMarkerDirection : GMapMarker
    {
        public float Ang;

        private Image image;
        public Image Image
        {
            get
            {
                return image;
            }
            set
            {
                image = value;
                if (image != null)
                {
                    this.Size = new Size(image.Width, image.Height);
                }
            }
        }

        public GMapMarkerDirection(PointLatLng p, Image image, float angle)
            : base(p)
        {

            Ang = angle - 90;
            if (Ang > 360)
            {
                Ang -= 360;
            }
            if (Ang < 0)
            {
                Ang += 360;
            }
            Image = image;
            Size = new System.Drawing.Size(image.Width, image.Height);
            Offset = new System.Drawing.Point(-Size.Width / 2, -Size.Height / 2);
        }

        public override void OnRender(Graphics g)
        {

            g.DrawImageUnscaled(RotateImage(Image, Ang), LocalPosition.X, LocalPosition.Y);
        }

        private Bitmap RotateImage(Image image, float angle)
        {
            if (image == null)
                throw new ArgumentNullException("image");

            const double pi2 = Math.PI / 2.0;
            double oldWidth = (double)image.Width;
            double oldHeight = (double)image.Height;
            double theta = ((double)angle) * Math.PI / 180.0;
            double locked_theta = theta;

            while (locked_theta < 0.0)
                locked_theta += 2 * Math.PI;

            double newWidth, newHeight;
            int nWidth, nHeight;

            #region Explaination of the calculations
            #endregion

            double adjacentTop, oppositeTop;
            double adjacentBottom, oppositeBottom;
            if ((locked_theta >= 0.0 && locked_theta < pi2) ||
                (locked_theta >= Math.PI && locked_theta < (Math.PI + pi2)))
            {
                adjacentTop = Math.Abs(Math.Cos(locked_theta)) * oldWidth;
                oppositeTop = Math.Abs(Math.Sin(locked_theta)) * oldWidth;

                adjacentBottom = Math.Abs(Math.Cos(locked_theta)) * oldHeight;
                oppositeBottom = Math.Abs(Math.Sin(locked_theta)) * oldHeight;
            }
            else
            {
                adjacentTop = Math.Abs(Math.Sin(locked_theta)) * oldHeight;
                oppositeTop = Math.Abs(Math.Cos(locked_theta)) * oldHeight;

                adjacentBottom = Math.Abs(Math.Sin(locked_theta)) * oldWidth;
                oppositeBottom = Math.Abs(Math.Cos(locked_theta)) * oldWidth;
            }

            newWidth = adjacentTop + oppositeBottom;
            newHeight = adjacentBottom + oppositeTop;

            nWidth = (int)Math.Ceiling(newWidth);
            nHeight = (int)Math.Ceiling(newHeight);

            Bitmap rotatedBmp = new Bitmap(nWidth, nHeight);

            using (Graphics g = Graphics.FromImage(rotatedBmp))
            {

                Point[] points;


                if (locked_theta >= 0.0 && locked_theta < pi2)
                {
                    points = new Point[] { 
                                             new Point( (int) oppositeBottom, 0 ), 
                                             new Point( nWidth, (int) oppositeTop ),
                                             new Point( 0, (int) adjacentBottom )
                                         };

                }
                else if (locked_theta >= pi2 && locked_theta < Math.PI)
                {
                    points = new Point[] { 
                                             new Point( nWidth, (int) oppositeTop ),
                                             new Point( (int) adjacentTop, nHeight ),
                                             new Point( (int) oppositeBottom, 0 )                         
                                         };
                }
                else if (locked_theta >= Math.PI && locked_theta < (Math.PI + pi2))
                {
                    points = new Point[] { 
                                             new Point( (int) adjacentTop, nHeight ), 
                                             new Point( 0, (int) adjacentBottom ),
                                             new Point( nWidth, (int) oppositeTop )
                                         };
                }
                else
                {
                    points = new Point[] { 
                                             new Point( 0, (int) adjacentBottom ), 
                                             new Point( (int) oppositeBottom, 0 ),
                                             new Point( (int) adjacentTop, nHeight )        
                                         };
                }

                g.DrawImage(image, points);
            }

            return rotatedBmp;
        }

    }

    Image image = Image.FromFile(Application.StartupPath + "\\markert.png");
    //location是坐标，image是market图片，max是旋转角度
    GMapMarkerDirection MyMarkss = new GMapMarkerDirection(location, image, max);
        GMapMarkerGoogleGreen gn = new GMapMarkerGoogleGreen(gMap_control.Position);
        MyMarkss.Markers.Add(gn);

        this.gMap_control.Overlays.Add(MyMarkss);
        gn.ToolTipMode = MarkerTooltipMode.Always;
        gn.ToolTipText = "提示信息"

5，在两点之间画线

    PointLatLng star = new PointLatLng();
    PointLatLng end= new PointLatLng();
    List<PointLatLng> list = new List<PointLatLng>();
    list.Add(star);
    list.Add(end);
    GMapOverlay routes = new GMapOverlay(this.gMap_control, "routes");
    this.gMap_control.Overlays.Add(routes);//添加到图层列表中  
    GMapRoute route = new GMapRoute(list, "action");
    routes.Routes.Add(route);

6，计算A点在B点的方向

    double angleOfLine = Math.Atan2((end.Lng - star.Lng), (end.Lat - star.Lat)) * 180 / Math.PI;
        int max = (int)angleOfLine;
        if (max > 360)
        {
           max -= 360;
        }
        if (max < 0)
        {
           max += 360;
        }