[SharpMap] 屏幕坐标和Map坐标转换

1. SharpMap中屏幕坐标和地图Map坐标转换：

 using System.Drawing;
 using GeoAPI.Geometries;

 namespace SharpMap.Utilities
 {
     /// <summary>
     /// Class for transforming between world and image coordinate
     /// </summary>
     public class Transform
     {
         /// <summary>
         /// Transforms from world coordinate system (WCS) to image coordinates
         /// 将世界坐标转换为image坐标
         /// NOTE: This method DOES NOT take the MapTransform property into account (use <see cref="Map.WorldToImage(GeoAPI.Geometries.Coordinate,bool)"/> instead)
         /// </summary>
         /// <param name="p">Point in WCS</param>
         /// <param name="map">Map reference</param>
         /// <returns>Point in image coordinates</returns>
         public static PointF WorldtoMap(Coordinate p, Map map)
         {
             //if (map.MapTransform != null && !map.MapTransform.IsIdentity)
             //    map.MapTransform.TransformPoints(new System.Drawing.PointF[] { p });
             if (p.IsEmpty())
                 return PointF.Empty;

             var result = new PointF();

             var height = (map.Zoom * map.Size.Height) / map.Size.Width;
             var left = map.Center.X - map.Zoom * 0.5;
             var top = map.Center.Y + height * 0.5 * map.PixelAspectRatio;
             result.X = (float)((p.X - left) / map.PixelWidth);
             result.Y = (float)((top - p.Y) / map.PixelHeight);
             if (double.IsNaN(result.X) || double.IsNaN(result.Y))
                 result = PointF.Empty;
             return result;
         }

         /// <summary>
         /// Transforms from image coordinates to world coordinate system (WCS).
         /// NOTE: This method DOES NOT take the MapTransform property into account (use <see cref="Map.ImageToWorld(System.Drawing.PointF,bool)"/> instead)
         /// </summary>
         /// <param name="p">Point in image coordinate system</param>
         /// <param name="map">Map reference</param>
         /// <returns>Point in WCS</returns>
         public static Coordinate MapToWorld(PointF p, Map map)
         {
             if (map.Center.IsEmpty() || double.IsNaN(map.MapHeight))
             {
                 return new Coordinate(, );
             }
             var ul = new Coordinate(map.Center.X - map.Zoom * ., map.Center.Y + map.MapHeight * .);
             return new Coordinate(ul.X + p.X * map.PixelWidth,
                                   ul.Y - p.Y * map.PixelHeight);
         }
     }
 }

Transform

详细分析: http://www.cnblogs.com/yhlx125/archive/2012/02/10/2342282.html

2. OpenS-CAD中的实现

已知屏幕分辨率每英寸像素点数，一般为96dpi，  定义float m_screenResolution = 96;

1. 初始化CanvasCtrl时，首先调用OnResize()方法。

 protected override void OnResize(EventArgs e)
         {
             base.OnResize(e);

             if (m_lastCenterPoint != UnitPoint.Empty && Width != )
                 SetCenterScreen(ToScreen(m_lastCenterPoint), false);
             m_lastCenterPoint = CenterPointUnit();
             m_staticImage = null;
             DoInvalidate(true);
         }

OnResize

由于m_lastCenterPoint是结构体变量，所以首先设置到中心点m_lastCenterPoint，即(0,0)，是Unit坐标

if (m_lastCenterPoint != UnitPoint.Empty && Width != 0)
    SetCenterScreen(ToScreen(m_lastCenterPoint), false);

接着调用m_lastCenterPoint = CenterPointUnit();

通过直角坐标的左上角点和右下角点计算。其实初始化时候执行该方法没有起到设置基准点的作用。可以跳过这2次，等窗体Resize的时候再看。

 public UnitPoint CenterPointUnit()
         {
             UnitPoint p1 = ScreenTopLeftToUnitPoint();
             UnitPoint p2 = ScreenBottomRightToUnitPoint();
             UnitPoint center = new UnitPoint();
             center.X = (p1.X + p2.X) / ;
             center.Y = (p1.Y + p2.Y) / ;
             return center;
         }
         public UnitPoint ScreenTopLeftToUnitPoint()
         {
             return ToUnit(new PointF(, ));
         }
         public UnitPoint ScreenBottomRightToUnitPoint()
         {
             return ToUnit(new PointF(this.ClientRectangle.Width, this.ClientRectangle.Height));
         }

CenterPointUnit

2. 接着打开文档DocumentForm，在构造的过程中设置文档画布的视点中心坐标为（0,0）。这样就实现了绘图画布原点坐标和屏幕（客户区）中心点的对应，形成基准点。默认的数据的长度单位为inch，屏幕坐标的单位为像素。这两者之间存在比例关系，通过Zoom缩放比例来实现尺度的变换，同时结合平移量和偏移距离计算出鼠标点的世界坐标。

m_canvas.SetCenter(new UnitPoint(0, 0));

或者加载完数据，设置画布的视点中心坐标。

m_canvas.SetCenter(m_data.CenterPoint);

 public DocumentForm(string filename)
         {
             InitializeComponent();

             Text = "<New Document>";
             m_data = new DataModel();
             if (filename.Length >  && File.Exists(filename) && m_data.Load(filename))
             {
                 Text = filename;
                 m_filename = filename;
             }

             m_canvas = new CanvasCtrl(this, m_data);
             m_canvas.Dock = DockStyle.Fill;
             Controls.Add(m_canvas);
             m_canvas.SetCenter(new UnitPoint(, ));
             m_canvas.RunningSnaps = new Type[]
                 {
                 typeof(VertextSnapPoint),
                 typeof(MidpointSnapPoint),
                 typeof(IntersectSnapPoint),
                 typeof(QuadrantSnapPoint),
                 typeof(CenterSnapPoint),
                 typeof(DivisionSnapPoint),
                 };

             m_canvas.AddQuickSnapType(Keys.N, typeof(NearestSnapPoint));
             m_canvas.AddQuickSnapType(Keys.M, typeof(MidpointSnapPoint));
             m_canvas.AddQuickSnapType(Keys.I, typeof(IntersectSnapPoint));
             m_canvas.AddQuickSnapType(Keys.V, typeof(VertextSnapPoint));
             m_canvas.AddQuickSnapType(Keys.P, typeof(PerpendicularSnapPoint));
             m_canvas.AddQuickSnapType(Keys.Q, typeof(QuadrantSnapPoint));
             m_canvas.AddQuickSnapType(Keys.C, typeof(CenterSnapPoint));
             m_canvas.AddQuickSnapType(Keys.T, typeof(TangentSnapPoint));
             m_canvas.AddQuickSnapType(Keys.D, typeof(DivisionSnapPoint));

             m_canvas.KeyDown += new KeyEventHandler(OnCanvasKeyDown);
             SetupMenuItems();
             SetupDrawTools();
             SetupLayerToolstrip();
             SetupEditTools();
             UpdateLayerUI();

             MenuStrip menuitem = new MenuStrip();//创建文档的主菜单
             menuitem.Items.Add(m_menuItems.GetMenuStrip("edit"));
             menuitem.Items.Add(m_menuItems.GetMenuStrip("draw"));
             menuitem.Visible = false;
             Controls.Add(menuitem);
             this.MainMenuStrip = menuitem;
         }
         protected override void OnLoad(EventArgs e)
         {
             base.OnLoad(e);
             m_canvas.SetCenter(m_data.CenterPoint);
         }

　　2.1查看SetCenter(UnitPoint unitPoint)方法，首先调用PointF point = ToScreen(unitPoint);将unitPoint转换PointF point.找到地图原点对应的屏幕坐标，应该是屏幕左下角点偏移(25,-25)。

         /// <summary>
         /// 设置画布到屏幕的中心
         /// </summary>
         /// <param name="rPoint">直角坐标系坐标</param>
         public void SetCenter(RPoint unitPoint)
         {
             //将unitPoint点对应到屏幕上point
             PointF point = Transform.ToScreen(unitPoint, this);
             m_lastCenterPoint = unitPoint;
             //将unitPoint偏移到屏幕中心
             SetCenterScreen(point, false);
         }

SetCenter

　这里注意计算Unit坐标到屏幕坐标的ToScreen()方法中，transformedPoint.Y = ScreenHeight() - transformedPoint.Y;//将Unit坐标系转换为屏幕坐标系，Y轴反向

　其中ScreenHeight()方法似乎有点问题，修改后如下。

  /// <summary>
         /// 将Unit坐标转换到屏幕坐标
         /// </summary>
         /// <param name="point"></param>
         /// <returns></returns>
         public PointF ToScreen(UnitPoint point)
         {
             PointF transformedPoint = Translate(point);
             transformedPoint.Y = ScreenHeight() - transformedPoint.Y;//将Unit坐标系转换为屏幕坐标系，Y轴反向
             transformedPoint.Y *= m_screenResolution * m_model.Zoom;
             transformedPoint.X *= m_screenResolution * m_model.Zoom;

             transformedPoint.X += m_panOffset.X + m_dragOffset.X;
             transformedPoint.Y += m_panOffset.Y + m_dragOffset.Y;
             return transformedPoint;
         }

ToScreen

 float ScreenHeight()
         {
             return (float)(ToUnit(this.ClientRectangle.Height));
             //return (float)(ToUnit(this.ClientRectangle.Height) / m_model.Zoom);
         }

ScreenHeight

　　 这样就引出了ToUnit(float screenvalue)函数，将屏幕距离转换为英寸数。

 public double ToUnit(float screenvalue)
         {
             return (double)screenvalue / (double)(m_screenResolution * m_model.Zoom);
         }

3. 接着将unitPoint赋值给m_lastCenterPoint

m_lastCenterPoint = unitPoint;

SetCenterScreen(point, false);

调用了SetCenterScreen()方法，

 protected  void SetCenterScreen(PointF screenPoint, bool setCursor)
         {
             float centerX = ClientRectangle.Width / ;
             m_panOffset.X += centerX - screenPoint.X;

             float centerY = ClientRectangle.Height / ;
             m_panOffset.Y += centerY - screenPoint.Y;

             if (setCursor)
                 Cursor.Position = this.PointToScreen(new Point((int)centerX, (int)centerY));
             DoInvalidate(true);
         }

4.理解了public PointF ToScreen(UnitPoint point)，那public UnitPoint ToUnit(PointF screenpoint)也好理解了。

  /// <summary>
         ///  将屏幕坐标转换到Unit坐标
         /// </summary>
         /// <param name="screenpoint"></param>
         /// <returns></returns>
         public UnitPoint ToUnit(PointF screenpoint)
         {
             float panoffsetX = m_panOffset.X + m_dragOffset.X;
             float panoffsetY = m_panOffset.Y + m_dragOffset.Y;
             float xpos = (screenpoint.X - panoffsetX) / (m_screenResolution * m_model.Zoom);
             float ypos = ScreenHeight() - ((screenpoint.Y - panoffsetY)) / (m_screenResolution * m_model.Zoom);
             return new UnitPoint(xpos, ypos);
         }

ToUnit

5.最后单独说一下ToScreen(UnitPoint point)和ToUnit(PointF screenpoint)中的两个变量

PointF m_panOffset = new PointF(, -);
PointF m_dragOffset = new PointF(, );

这里m_panOffset控制的是中心点Center的偏移量，是一个累计的量，相对于中心点。

m_dragOffset记录了每次移动过程中的移动量，每次产生一个新值。每次CanvasCtrl控件的OnMouseDown时累积到偏移量上，之后重新初始化，同时在OnMouseUp时的移动命令下重新初始化（如下代码），似乎重复了。

 if (m_commandType == eCommandType.pan)
             {
                 m_panOffset.X += m_dragOffset.X;
                 m_panOffset.Y += m_dragOffset.Y;
                 m_dragOffset = new PointF(, );
             }

在protected override void OnMouseMove(MouseEventArgs e)事件中

 if (m_commandType == eCommandType.pan && e.Button == MouseButtons.Left)
             {
                 m_dragOffset.X = -(m_mousedownPoint.X - e.X);
                 m_dragOffset.Y = -(m_mousedownPoint.Y - e.Y);
                 m_lastCenterPoint = CenterPointUnit();
                 DoInvalidate(true);
             }

可知，m_dragOffset和m_panOffset记录的是偏移的屏幕坐标。