GeoJson文件使用示例

本节提供了几个读取GeoJson文件生成地图的文件。

关于json数据的解析，可参考： json解析

Map控件提供了一个CreatFromJsonObject方法，用于根据Feature节点生成对应的地图对象，其语法为：

CreatFromJsonObject(Feature，MaxCount)

Feature： JObject类型，GeoJson文件中的一个Feature节点。
MaxCount：可选参数，对于MultiLineString和MultiPolygon类型的数据，可用此参数设置生成的线条和多边形的最大数量。

示例一

本示例内容可以参考CaseStudy目录下的文件"地图.Table"的示例二十。

本示例使用了CaseStudy目录下的GeoJson文件"中国.json"

1、将Map控件的"地图来源"属性设置为"None"

2、将窗口的AfterLoad事件代码设置为：

Dim map As GeoMap = e.Form.Controls("Map1").GeoMap
Dim layer As New VectorLayer()
layer.Style.Stroke.Color = Color.DarkGray
layer.LabelVisibility = LabelVisibility.AutoHide
map.Layers.Add(layer)
Dim file As String = ProjectPath & "中国.json"
Dim jo As JObject = JObject.Parse(FileSys.ReadAllText(file))
For Each jt As JToken In jo("features") '遍历feature节点
    Dim data As JToken = jt("properties") '获取属性节点
    Dim type As String = jt("geometry")("type") '获取节点数据类型
    If type = "MultiPolygon" OrElse type = "Polygon" Then '如果类型为多边形
        Dim polygon As VectorPolygon = map.CreatFromJsonObject(jt) '创建多边形
        polygon.Tag = data("name")
        If data("name") = "安徽省" Then
            polygon.Style.BackColor = Color.BlueViolet
        Else If data("name") = "北京市" Then
            Dim mark As New VectorPlacemark()
            mark.Marker.Size = New Size(16, 16)
            mark.Geometry = New GeoPoint(data("center")(0), data("center")(1))
            mark.Marker.Shape = MarkerShape.Star
            Mark.Style.BackColor = Color.Red
            mark.Style.Stroke.Color = Color.Red
            mark.Marker.Caption = "北京"
            mark.LabelStyle.ForeColor = Color.Green
            mark.Marker.LabelPosition = LabelPosition.Right
            layer.Items.Add(mark)
        End If
        layer.Items.Add(polygon)
    End If
Next

生成的地图为：

示例二

本示例内容可以参考CaseStudy目录下的文件"地图.Table"的示例二十一。

本示例使用了CaseStudy目录下的GeoJson文件:

中国.json
省会,json
长江.json
G65.json

其中“省会.json”为中国给省会城市的经纬度坐标，“长江.json”为长江干流的走向，"G65.json"为G65高速(茂名方向)的走向。

1、将Map控件的"地图来源"属性设置为"None"

2、将窗口的AfterLoad事件代码设置为：

Dim map As GeoMap = e.Form.Controls("Map1").GeoMap
Dim layer As New VectorLayer()
layer.Style.Stroke.Color = Color.DarkGray
layer.LabelVisibility = LabelVisibility.AutoHide
map.Layers.Add(layer)
Dim files() As String = {"中国.json", "省会.json", "长江.json", "G65.json"｝
For Each file As String In files
    Dim jo As JObject = JObject.Parse(FileSys.ReadAllText(ProjectPath & file))
    For Each jt As JToken In jo("features") '遍历feature节点
        Dim data As JToken = jt("properties") '获取属性节点
        Dim type As String = jt("geometry")("type") '获取节点数据类型
        Select Case type
            Case "MultiPolygon" , "Polygon"
                layer.Items.Add(map.CreatFromJsonObject(jt))
            Case "Point", "MultiPoint"
                Dim mark As VectorPlacemark = map.CreatFromJsonObject(jt)
                mark.Marker.Caption = data("name")
                mark.Marker.LabelPosition = LabelPosition.Right
                If data("name") = "北京" Then
                    mark.Marker.Shape = MarkerShape.Star
                    mark.Style.Stroke.Color = Color.Red
                    mark.Style.BackColor = Color.Red
                    mark.Marker.Size = New Size(16, 16)
                Else
                    mark.Marker.Shape = MarkerShape.Circle
                    mark.Style.Stroke.Color = Color.Green
                    mark.Style.BackColor = Color.Green
                    mark.Marker.Size = New Size(6, 6)
                End If
                layer.Items.Add(mark)
            Case "LineString", "MultiLineString"
                Dim line As VectorPolyline = map.CreatFromJsonObject(jt)
                line.Style.Stroke.Width = 2
                If data("type") = "river"  Then'如果是河流
                    line.Style.Stroke.Color = Color.Blue
                ElseIf data("type") = "highway" Then'如果是高速公路
                    line.Style.Stroke.Color = Color.Red
                    line.Style.Stroke.Style = GeoDashStyle.Dash
                End if
                layer.Items.Add(line)
        End Select
    Next
Next

生成的地图为：

示例三

本示例内容可以参考CaseStudy目录下的文件"地图.Table"的示例二十二。

各种地图数据可以混用，我们可以基于行政区域表绘制地图，然后基于GeoJso绘制高速或河流：

1、将Map控件的"地图来源"属性设置为"None"

2、将窗口的AfterLoad事件代码设置为：

Dim map As GeoMap = e.Form.Controls("Map1").GeoMap
'基于GeoJson文件绘制一条高速
Dim layer As New VectorLayer()
map.Layers.Add(layer)
Dim jo As JObject = JObject.Parse(FileSys.ReadAllText(ProjectPath & "G65.json"))
For Each jt As JToken In jo("features") '遍历feature节点
    Dim data As JToken = jt("properties") '获取属性节点
    Dim line As VectorPolyline = map.CreatFromJsonObject(jt)
    line.Style.Stroke.Width = 2
    line.Style.Stroke.Color = Color.Blue
    line.Style.Stroke.Style = GeoDashStyle.Dash
    layer.Items.Add(line)
Next
'基于行政区域表绘制地图
For level As Integer = 1 To 2
    layer = New VectorLayer() '每一级行政区一个图层
    map.Layers.Add(layer)
    layer.Style.Stroke.Color = Color.FromArgb(50, 255, 0, 0)
    layer.LabelVisibility = LabelVisibility.AutoHide
    layer.LabelStyle.ForeColor = Color.Green
    If level = 1 Then
        layer.MaxZoom = 4.5 '缩放比例小于4.5时显示省级行政区
    ElseIf level = 2 Then
        layer.MinZoom = 4.5 '缩放比例超过4.5之后显示市级行政区
    End If
    For Each dr As DataRow In DataTables("行政区域").Select("level= " & level)
        layer.Items.Add(map.CreatePolygon(dr("geometry"), 5))
        If level = 2 OrElse "北京市天津市上海市重庆市".Contains(dr("name")) Then '如果是地级市或直辖市
            Dim mark As New VectorPlacemark()
            mark.Marker.Shape = MarkerShape.Circle
            mark.Style.BackColor = Color.Blue
            mark.Marker.Size = New Size(6, 6)
            mark.Marker.LabelPosition = LabelPosition.Right
            mark.Marker.Caption = dr("name")
            mark.Geometry = New GeoPoint(dr("centerX"), dr("centerY"))
            layer.Items.Add(mark)
        End If
    Next
Next

生成的地图为：

放大地图后会显示G65经过的城市：