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

Question

我有 C# 应用程序，它使用 GMap.NET 来呈现世界地图和我的其他数据。我有要渲染的 Graphics 对象。我还需要在我的地图上将 ESRI 形状文件显示为半透明形状。我该如何渲染它？可用的库看起来就像它们会吸引到自己的 Windows 控件中。另外，当我能够渲染它时，如何准确同步地图和形状坐标？

感谢：D。

Answer 1

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

您必须首先使用 (MapTools) 库读取形状文件，并为每个几何图形（点、线、多边形）循环，然后使用Proj4Net库转换几何投影，并将每个几何图形添加到 GMapControl 上的适当叠加层。

您可以从此链接下载 (MapTools) 的最新版本

这是一个读取填充了路线的形状文件的示例函数，它将返回 GMapRoutes 列表，然后您必须在地图上绘制它们。

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