GMap.Net开发之技巧小结

1、在GMap地图上，如果要让添加的图标（Marker）有个高亮（highlight）的效果，可以在MouseOver到Marker的时候设置Marker外观效果。

如果要让图标有个报警闪烁的效果，可以设置一个定时器，在定时器中改变Marker的外观，或者是用GDI来画圆闪动，带报警效果的Marker如下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using GMap.NET;
using GMap.NET.WindowsForms;
using System.Drawing;
using System.Windows.Forms;

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

        public bool IsHighlight = true;
        public Pen HighlightPen { set; get; }

        public Pen FlashPen { set; get; }
        private Timer flashTimer = new Timer();

        private int radius;
        private int flashRadius;

        public GMapMarkerImage(GMap.NET.PointLatLng p, Image image)
            : base(p)
        {
            Size = new System.Drawing.Size(image.Width, image.Height);
            Offset = new System.Drawing.Point(-Size.Width / 2, -Size.Height / 2);
            Image = image;
            HighlightPen = new System.Drawing.Pen(Brushes.Red,2);
            radius = Size.Width >= Size.Height ? Size.Width : Size.Height;
            flashTimer.Interval = 10;
            flashTimer.Tick += new EventHandler(flashTimer_Tick);
        }

        public void StartFlash()
        {
            flashTimer.Start();
        }


        void flashTimer_Tick(object sender, EventArgs e)
        {
            if (FlashPen == null)
            {
                FlashPen = new Pen(Brushes.Red, 3);
                flashRadius = radius;
            }
            else
            {
                flashRadius += radius/4;
                if (flashRadius >= 2 * radius)
                {
                    flashRadius = radius;
                    FlashPen.Color = Color.FromArgb(255, Color.Red);
                }
                else
                {
                    Random rand = new Random();
                    int alpha = rand.Next(255);
                    FlashPen.Color = Color.FromArgb(alpha, Color.Red);
                }
            }
            this.Overlay.Control.Refresh();
        }

        public void StopFlash()
        {
            flashTimer.Stop();
            if (FlashPen != null)
            {
                FlashPen.Dispose();
                FlashPen = null;
            }
            this.Overlay.Control.Refresh();
        }

        public override void OnRender(Graphics g)
        {
            if (image == null)
                return;

            Rectangle rect = new Rectangle(LocalPosition.X, LocalPosition.Y, Size.Width, Size.Height);
            g.DrawImage(image, rect);

            if (IsMouseOver && IsHighlight)
            {
                g.DrawRectangle(HighlightPen,rect);
            }

            if (FlashPen != null)
            {
                g.DrawEllipse(FlashPen,
                    new Rectangle(LocalPosition.X - flashRadius / 2 + Size.Width/2, LocalPosition.Y - flashRadius / 2+Size.Height/2, flashRadius, flashRadius));
            }
        }

        public override void Dispose()
        {
            if (HighlightPen != null)
            {
                HighlightPen.Dispose();
                HighlightPen = null;
            }

            if (FlashPen != null)
            {
                FlashPen.Dispose();
                FlashPen = null;
            }

            base.Dispose();
        }
    }
}

2、可以旋转角度的Marker，比如可以将一个箭头图标旋转一定角度来指向一个轨迹路线，代码如下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Drawing;
using GMap.NET;
using GMap.NET.WindowsForms;
using GMapWinFormDemo.Properties;

namespace GMapWinFormDemo
{
    class GMapMarkerDirection : GMapMarker
    {
        private 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;
            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);
        }

        //http://www.codeproject.com/KB/graphics/rotateimage.aspx
        //Author : James T. Johnson
        private static Bitmap RotateImage(Image image, float angle)
        {
            if (image == null)
                throw new ArgumentNullException("image");

            const double pi2 = Math.PI / 2.0;

            // Why can't C# allow these to be const, or at least readonly
            // *sigh*  I'm starting to talk like Christian Graus :omg:
            double oldWidth = (double)image.Width;
            double oldHeight = (double)image.Height;

            // Convert degrees to radians
            double theta = ((double)angle) * Math.PI / 180.0;
            double locked_theta = theta;

            // Ensure theta is now [0, 2pi)
            while (locked_theta < 0.0)
                locked_theta += 2 * Math.PI;

            double newWidth, newHeight;
            int nWidth, nHeight; // The newWidth/newHeight expressed as ints

            #region Explaination of the calculations
            /*
             * The trig involved in calculating the new width and height
             * is fairly simple; the hard part was remembering that when 
             * PI/2 <= theta <= PI and 3PI/2 <= theta < 2PI the width and 
             * height are switched.
             * 
             * When you rotate a rectangle, r, the bounding box surrounding r
             * contains for right-triangles of empty space.  Each of the 
             * triangles hypotenuse's are a known length, either the width or
             * the height of r.  Because we know the length of the hypotenuse
             * and we have a known angle of rotation, we can use the trig
             * function identities to find the length of the other two sides.
             * 
             * sine = opposite/hypotenuse
             * cosine = adjacent/hypotenuse
             * 
             * solving for the unknown we get
             * 
             * opposite = sine * hypotenuse
             * adjacent = cosine * hypotenuse
             * 
             * Another interesting point about these triangles is that there
             * are only two different triangles. The proof for which is easy
             * to see, but its been too long since I've written a proof that
             * I can't explain it well enough to want to publish it.  
             * 
             * Just trust me when I say the triangles formed by the lengths 
             * width are always the same (for a given theta) and the same 
             * goes for the height of r.
             * 
             * Rather than associate the opposite/adjacent sides with the
             * width and height of the original bitmap, I'll associate them
             * based on their position.
             * 
             * adjacent/oppositeTop will refer to the triangles making up the 
             * upper right and lower left corners
             * 
             * adjacent/oppositeBottom will refer to the triangles making up 
             * the upper left and lower right corners
             * 
             * The names are based on the right side corners, because thats 
             * where I did my work on paper (the right side).
             * 
             * Now if you draw this out, you will see that the width of the 
             * bounding box is calculated by adding together adjacentTop and 
             * oppositeBottom while the height is calculate by adding 
             * together adjacentBottom and oppositeTop.
             */
            #endregion

            double adjacentTop, oppositeTop;
            double adjacentBottom, oppositeBottom;

            // We need to calculate the sides of the triangles based
            // on how much rotation is being done to the bitmap.
            //   Refer to the first paragraph in the explaination above for 
            //   reasons why.
            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))
            {
                // This array will be used to pass in the three points that 
                // make up the rotated image
                Point[] points;

                /*
                 * The values of opposite/adjacentTop/Bottom are referring to 
                 * fixed locations instead of in relation to the
                 * rotating image so I need to change which values are used
                 * based on the how much the image is rotating.
                 * 
                 * For each point, one of the coordinates will always be 0, 
                 * nWidth, or nHeight.  This because the Bitmap we are drawing on
                 * is the bounding box for the rotated bitmap.  If both of the 
                 * corrdinates for any of the given points wasn't in the set above
                 * then the bitmap we are drawing on WOULDN'T be the bounding box
                 * as required.
                 */
                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;
        }

    }
}

3、在点击图标Marker的时候出现ContextMenuStrip：

        void mapControl_OnMarkerClick(GMapMarker item, MouseEventArgs e)
        {
            if (e.Button == System.Windows.Forms.MouseButtons.Left)
            {
                this.contextMenuStrip1.Show(Cursor.Position);
                if (item is GMapMarkerImage)
                {
                    currentMarker = item as GMapMarkerImage;
                }
            }
        }

4、随地图放大缩小的圆，代码来自官方Demo：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Drawing;
using GMap.NET;
using GMap.NET.WindowsForms;

namespace GMapWinFormDemo
{
    public class GMapMarkerCircle : GMapMarker
    {
        /// <summary>
        /// In Meters
        /// </summary>
        public int Radius;

        /// <summary>
        /// specifies how the outline is painted
        /// </summary>
        public Pen Stroke = new Pen(Color.FromArgb(155, Color.MidnightBlue));

        /// <summary>
        /// background color
        /// </summary>
        public Brush Fill = new SolidBrush(Color.FromArgb(155, Color.AliceBlue));

        /// <summary>
        /// is filled
        /// </summary>
        public bool IsFilled = true;

        public GMapMarkerCircle(PointLatLng p)
            : base(p)
        {
            Radius = 100; // 100m
            IsHitTestVisible = false;
        }

        public override void OnRender(Graphics g)
        {
            int R = (int)((Radius) / Overlay.Control.MapProvider.Projection.GetGroundResolution((int)Overlay.Control.Zoom, Position.Lat)) * 2;

            if (IsFilled)
            {
                g.FillEllipse(Fill, new System.Drawing.Rectangle(LocalPosition.X - R / 2, LocalPosition.Y - R / 2, R, R));
            }
            g.DrawEllipse(Stroke, new System.Drawing.Rectangle(LocalPosition.X - R / 2, LocalPosition.Y - R / 2, R, R));
        }

        public override void Dispose()
        {
            if (Stroke != null)
            {
                Stroke.Dispose();
                Stroke = null;
            }

            if (Fill != null)
            {
                Fill.Dispose();
                Fill = null;
            }

            base.Dispose();
        }
    }
}

关键就是如何在放大缩小时确定圆的半径大小，半径大小为：

int R = (int)((Radius) / Overlay.Control.MapProvider.Projection.GetGroundResolution((int)Overlay.Control.Zoom, Position.Lat)) * 2;

通过当前的缩放比例zoom和圆心的纬度来得到地图在此条件下分辨率（resolution），分辨率的大小为一个像素大小所代表的距离（单位为米）。

所以当我采用画多边形的方式在地图上画圆时，实际得到的圆在小半径和地球赤道附近下是个圆，但是在纬度较大的地方画的圆就变成了椭圆，代码如下：

namespace GMapWinFormDemo
{
    public static class CirclePolygon
    {
        public static GMapPolygon CreateCircle(PointLatLng center, double radius, string name)
        {
            List<PointLatLng> pList = new List<PointLatLng>();
            int segments = 100000;
            double seg = 2 * Math.PI / segments;
            for (int i = 0; i < segments; ++i)
            {
                double theta = i * seg;
                double a = center.Lat + Math.Cos(theta) * radius;
                double b = center.Lng + Math.Sin(theta) * radius;
                pList.Add(new PointLatLng(a, b));
            }
            GMapPolygon circle = new GMapPolygon(pList, name);
            circle.Stroke = new Pen(Brushes.Red, 1);
            return circle;
        }
    }
}

5、保存地图为图片：

        private void buttonSaveMap_Click(object sender, EventArgs e)
        {
            try
            {
                using (SaveFileDialog dialog = new SaveFileDialog())
                {
                    dialog.Filter = "PNG (*.png)|*.png";
                    dialog.FileName = "GMap.NET image";
                    Image image = this.mapControl.ToImage();
                    if (image != null)
                    {
                        using (image)
                        {
                            if (dialog.ShowDialog() == DialogResult.OK)
                            {
                                string fileName = dialog.FileName;
                                if (!fileName.EndsWith(".png", StringComparison.OrdinalIgnoreCase))
                                {
                                    fileName += ".png";
                                }
                                image.Save(fileName);
                                MessageBox.Show("图片已保存： " + dialog.FileName, "GMap.NET", MessageBoxButtons.OK, MessageBoxIcon.Asterisk);
                            }
                        }
                    }
                }
            }
            catch (Exception exception)
            {
                MessageBox.Show("图片保存失败： " + exception.Message, "GMap.NET", MessageBoxButtons.OK, MessageBoxIcon.Hand);
            }
        }

项目地址：https://github.com/luxiaoxun/MapDownloader

参考：

https://greatmaps.codeplex.com/