c# - 如何在 GMap.NET 输出之上或使用我的图形对象绘制 ESRI 形状

Question

我有 C# 应用程序，它使用 GMap.NET 渲染世界地图和我的其他数据。我有要渲染到的 Graphics 对象。我还需要在我的 map 上将 ESRI 形状文件显示为半透明形状。我如何渲染它？可用的库看起来像是将绘制到自己的 Windows 控件中。另外，当我能够渲染它时，如何准确同步 map 和形状坐标？

谢谢，D.

Answer 1

GMap.Net 不支持直接读取 ESRI 形状文件，但您可以使用第 3 方库，如 MapTools它是 (ShapeLib) 库的 .Net 包装器。

您必须首先使用 (MapTools) 库读取形状文件并循环处理每个几何体(点、线、多边形)，然后使用 Proj4Net Libarary 转换几何体投影并将每个几何图形添加到其在 GMapControl 上的适当叠加层。

您可以从this link 下载最新版本的(MapTools)。

下面是一个读取充满路线的形状文件的示例函数，它将返回 GMapRoutes 列表，然后您必须在 map 上绘制它们。

Public  Function ReadRoutesFromShapefile(ByVal filename As String) As List(Of GMapRoute)

        Dim basePath As String = Path.GetDirectoryName(filename) & AscW(Path.DirectorySeparatorChar) & Path.GetFileNameWithoutExtension(filename)

        If Not File.Exists(basePath & ".prj") Then
            Throw New Exception("Could not find the projection file!")
        End If

        'Get info from WKT-File:
        Dim wkt As String = File.ReadAllText(basePath & ".prj")

        Dim gcs As ICoordinateSystem = TryCast(CoordinateSystemWktReader.Parse(wkt), ICoordinateSystem)
        Dim doTransformation = Not gcs.AuthorityCode = 4326

        Dim wgs84 As GeographicCoordinateSystem = GeographicCoordinateSystem.WGS84
        Dim ctfac As New CoordinateTransformationFactory()
        Dim trans As ICoordinateTransformation = ctfac.CreateFromCoordinateSystems(gcs, wgs84)

        'Open shape-file
        Dim shapeFile As IntPtr = ShapeLib.SHPOpen(basePath, "rb")

        Dim numOfRecords As Integer = 0

        'Check type and get number of entries
        Dim shapeType As ShapeLib.ShapeType = 0
        ShapeLib.SHPGetInfo(shapeFile, numOfRecords, shapeType, Nothing, Nothing)

        If Not shapeType.Equals(ShapeLib.ShapeType.PolyLine) Then
            Throw New Exception("The shape type is not polyline but " & shapeType)
        End If

        Dim lstRoutes As New List(Of GMapRoute)(numOfRecords)

        'Get info from shapefile and save data:
        For i As Integer = 0 To numOfRecords - 1
            'Add all GPS-Points:
            'Get pointer to object
            Dim ptrPolyline As IntPtr = ShapeLib.SHPReadObject(shapeFile, i)

            'Create actual object:
            Dim polyline As New ShapeLib.SHPObject()
            Marshal.PtrToStructure(ptrPolyline, polyline)

            If polyline.nParts = 1 Then
                'Get number of points and arrays of X and Y values:
                Dim numPoints As Integer = polyline.nVertices

                Dim lstpoints As New List(Of PointLatLng)(numPoints)

                Dim xCoord(numPoints - 1) As Double
                Dim yCoord(numPoints - 1) As Double

                'Fill the arrays:
                Marshal.Copy(polyline.padfX, xCoord, 0, numPoints)
                Marshal.Copy(polyline.padfY, yCoord, 0, numPoints)

                'Add all Points
                For j As Integer = 0 To numPoints - 1
                    Dim latitude As Double = 0.0R
                    Dim longitude As Double = 0.0R

                    If doTransformation Then
                        'Convert from original coordinate system to wgs84
                        Dim fromPoint() As Double = {xCoord(j), yCoord(j)}
                        Dim toPoint() As Double = trans.MathTransform.Transform(fromPoint)
                        'Get point from polyline
                        longitude = toPoint(0)
                        latitude = toPoint(1)
                    Else
                        longitude = xCoord(j)
                        latitude = yCoord(j)
                    End If

                    lstpoints.Add(New PointLatLng(latitude, longitude))
                Next j

                lstRoutes.Add(New GMapRoute(lstpoints, "Route" & (i + 1).ToString()))
            End If

            polyline = Nothing
            ShapeLib.SHPDestroyObject(ptrPolyline)
        Next i

        ShapeLib.SHPClose(shapeFile)

        Return lstRoutes
    End Function