private void AddMarkers(GMapOverlay overlay, List <NearByResult> points)
        {
            mainMarker = new GMapMarkerWithLabel(
                new PointLatLng(coord.Latitude, coord.Longitude), GMarkerGoogleType.red, "目前位置", Color.Red);
            overlay.Markers.Add(mainMarker);

            for (int i = 0; i < points.Count; i++)
            {
                PointLatLng point = new PointLatLng(points[i].Geometry.Location.Latitude, points[i].Geometry.Location.Longitude);

                GMapMarkerWithLabel marker = new GMapMarkerWithLabel(point, GMarkerGoogleType.green, points[i].Name, Color.Green);
                marker.ToolTipText = "\n" + points[i].Name;

                marker.ToolTip.TextPadding = new Size((int)marker.ToolTip.Font.Height, (int)marker.ToolTip.Font.Height);

                overlay.Markers.Add(marker);
            }
            overlay.IsVisibile = false;
            overlay.IsVisibile = true;
        }
        //todo
        private void gMapControl1_OnMapZoomChanged()
        {
            this.overlayTwo.SetZoomLevel(this.gMapControl1.Zoom);

            if (this.gMapControl1.Zoom == 18)
            {
                for (int i = 0; i < overlayOne.Markers.Count; i++)
                {
                    GMapMarkerWithLabel marker = overlayOne.Markers[i] as GMapMarkerWithLabel;
                    //marker.SetZoomLevel(this.gMapControl1.Zoom);
                    marker.ToolTipMode = MarkerTooltipMode.Never;
                }
            }
            else
            {
                for (int i = 0; i < overlayOne.Markers.Count; i++)
                {
                    GMapMarkerWithLabel marker = overlayOne.Markers[i] as GMapMarkerWithLabel;
                    //marker.SetZoomLevel(this.gMapControl1.Zoom);
                    marker.ToolTipMode = MarkerTooltipMode.OnMouseOver;
                }
            }
        }