空间数据类型（几何）到GeoJSON

Question

我想将geom（geometry）数据类型转换为GeoJSON。我该怎么办？

例如，WKT中的几何：

    POLYGON((455216.346127297 4288433.28426224,455203.386722146 4288427.76317716,455207.791765017 4288417.51116228,455220.784166744 4288423.30230044,455216.346127297 4288433.28426224))

转到以下GeoJSON：

{ "type": "Polygon",
    "coordinates": [
      [ [100.0, 0.0], [101.0, 0.0], [101.0, 1.0], [100.0, 1.0], [100.0, 0.0] ],
      [ [100.2, 0.2], [100.8, 0.2], [100.8, 0.8], [100.2, 0.8], [100.2, 0.2] ]
    ]
}

Answer 1

我也有同样的需求。我们有一个大型数据库，其中包含 SQL Server 中带有 GEOMETRY 列的表。我觉得能够从包含 GeoJson 的存储过程中获取单个字符串对象是更可取的。我编写了一个函数，它将几何实例作为对象并返回一个 GeoJson 字符串。

CREATE FUNCTION [dbo].[geomToGeoJSON] (@geom GEOMETRY)
RETURNS VARCHAR(MAX)
AS
BEGIN
-- Declare the return variable here
    DECLARE @geoJSON VARCHAR(MAX)


    DECLARE @Ngeom GEOMETRY
    DECLARE @ptCounter INT
    DECLARE @numPt INT
    DECLARE @ringCounter INT
    DECLARE @numRing INT
    DECLARE @gCounter INT
    DECLARE @numGeom INT
    DECLARE @handled BIT = 0
    DECLARE @extRing GEOMETRY
    DECLARE @intRing GEOMETRY

    -- fix bad geometries and enforce ring orientation
    SET @geom = @geom.STUnion(@geom.STPointN(1)).MakeValid()

    -- Point ----------------------------
    IF (@geom.STGeometryType() = 'Point')
    BEGIN
        SET @geoJSON = '{ "type": "Point", "coordinates": [' + LTRIM(RTRIM(STR(@geom.STX, 38, 8))) + ', ' + LTRIM(RTRIM(STR(@geom.STY, 38, 8))) + '] }'
        SET @handled = 1
    END


    -- MultiPoint ---------------------------------------------
    IF (
        @handled = 0
        AND @geom.STGeometryType() = 'MultiPoint'
        )
    BEGIN
        SET @gCounter = 1
        SET @numGeom = @geom.STNumGeometries()

        SET @geoJSON = '{ "type": "MultiPoint", "coordinates": ['

        WHILE @gCounter <= @numGeom
        BEGIN
            SET @geoJSON += '[' + LTRIM(RTRIM(STR(@geom.STGeometryN(@gCounter).STX, 38, 8))) + ', ' + LTRIM(RTRIM(STR(@geom.STGeometryN(@gCounter).STY, 38, 8))) + '], '
            SET @gCounter += 1
        END

        SET @geoJSON = LEFT(@geoJSON, LEN(@geoJSON) - 1) + '] }'
        SET @handled = 1
    END




    -- LineString ---------------------------------------------
    IF (
        @handled = 0
        AND @geom.STGeometryType() = 'LineString'
        )
    BEGIN
        SET @ptCounter = 1
        SET @numPt = @geom.STNumPoints()

        SET @geoJSON = '{ "type": "LineString", "coordinates": ['

        WHILE @ptCounter <= @numPt
        BEGIN
            SET @geoJSON += '[' + LTRIM(RTRIM(STR(@geom.STPointN(@ptCounter).STX, 38, 8))) + ', ' + LTRIM(RTRIM(STR(@geom.STPointN(@ptCounter).STY, 38, 8))) + '], '
            SET @ptCounter += 1
        END

        SET @geoJSON = LEFT(@geoJSON, LEN(@geoJSON) - 1) + ' ] }'
        SET @handled = 1
    END




    -- MultiLineString ---------------------------------------------
    IF (
        @handled = 0
        AND @geom.STGeometryType() = 'MultiLineString'
        )
    BEGIN
        SET @gCounter = 1
        SET @numGeom = @geom.STNumGeometries()

        SET @geoJSON = '{ "type": "MultiLineString", "coordinates": ['

        WHILE @gCounter <= @numGeom
        BEGIN
            SET @Ngeom = @geom.STGeometryN(@gCounter)
            SET @geoJSON += '['
            SELECT
                @ptCounter = 1
                ,@numPt = @Ngeom.STNumPoints()

            WHILE @ptCounter <= @numPt
            BEGIN
                SET @geoJSON += '[' + LTRIM(RTRIM(STR(@Ngeom.STPointN(@ptCounter).STX, 38, 8))) + ', ' + LTRIM(RTRIM(STR(@Ngeom.STPointN(@ptCounter).STY, 38, 8))) + '], '
                SET @ptCounter += 1
            END

            SET @geoJSON = LEFT(@geoJSON, LEN(@geoJSON) - 1) + '],'

            SET @gCounter += 1
        END

        SET @geoJSON = LEFT(@geoJSON, LEN(@geoJSON) - 1) + '] }'
        SET @handled = 1
    END




    -- Polygon ---------------------------------------------
    IF (
        @handled = 0
        AND @geom.STGeometryType() = 'Polygon'
        )
    BEGIN
        SET @extRing = @geom.STExteriorRing()

        SET @geoJSON = '{ "type": "Polygon", "coordinates": [['

        SELECT
            @ptCounter = 1
            ,@numPt = @extRing.STNumPoints()

        WHILE @ptCounter <= @numPt
        BEGIN
            SET @geoJSON += '[' + LTRIM(RTRIM(STR(@extRing.STPointN(@ptCounter).STX, 38, 8))) + ', ' + LTRIM(RTRIM(STR(@extRing.STPointN(@ptCounter).STY, 38, 8))) + '], '
            SET @ptCounter += 1
        END

        SET @geoJSON = LEFT(@geoJSON, LEN(@geoJSON) - 1) + ']'

        SET @ringCounter = 1
        SET @numRing = @geom.STNumInteriorRing()

        WHILE @ringCounter <= @numRing
        BEGIN
            SET @geoJSON += ',['

            SET @intRing = @geom.STInteriorRingN(@ringCounter)
            -- set the ring orientation so that they are consistent
            SET @intRing = @intRing.STUnion(@intRing.STPointN(1)).MakeValid()

            SELECT
                @ptCounter = @intRing.STNumPoints()

            WHILE @ptCounter > 0
            BEGIN
                SET @geoJSON += '[' + LTRIM(RTRIM(STR(@intRing.STPointN(@ptCounter).STX, 38, 8))) + ', ' + LTRIM(RTRIM(STR(@intRing.STPointN(@ptCounter).STY, 38, 8))) + '], '
                SET @ptCounter -= 1
            END

            SET @geoJSON = LEFT(@geoJSON, LEN(@geoJSON) - 1) + ']'

            SET @ringCounter += 1
        END

        SET @geoJSON = LEFT(@geoJSON, LEN(@geoJSON) - 1) + ']] }'
        SET @handled = 1
    END




    -- MultiPolygon ---------------------------------------------
    IF (
        @handled = 0
        AND @geom.STGeometryType() = 'MultiPolygon'
        )
    BEGIN
        SELECT
            @gCounter = 1
            ,@numGeom = @geom.STNumGeometries()

        SET @geoJSON = '{ "type": "MultiPolygon", "coordinates": ['

        WHILE @gCounter <= @numGeom
        BEGIN
            SET @Ngeom = @geom.STGeometryN(@gCounter)

            SET @extRing = @Ngeom.STExteriorRing()

            SET @geoJSON += '[['

            SELECT
                @ptCounter = 1
                ,@numPt = @extRing.STNumPoints()

            -- add the exterior ring points to the json
            WHILE @ptCounter <= @numPt
            BEGIN
                SET @geoJSON += '[' + LTRIM(RTRIM(STR(@extRing.STPointN(@ptCounter).STX, 38, 8))) + ', ' + LTRIM(RTRIM(STR(@extRing.STPointN(@ptCounter).STY, 38, 8))) + '], '
                SET @ptCounter += 1
            END

            SET @geoJSON = LEFT(@geoJSON, LEN(@geoJSON) - 1) + ']'

            SET @ringCounter = 1
            SET @numRing = @Ngeom.STNumInteriorRing()

            -- add any internal ring points to the json
            WHILE @ringCounter <= @numRing
            BEGIN
                SET @geoJSON += ',['

                SET @intRing = @Ngeom.STInteriorRingN(@ringCounter)
                -- make sure the ring orientation is the same every time
                SET @intRing = @intRing.STUnion(@intRing.STPointN(1)).MakeValid()

                SELECT
                    @ptCounter = @intRing.STNumPoints()

                WHILE @ptCounter > 0
                BEGIN
                    SET @geoJSON += '[' + LTRIM(RTRIM(STR(@intRing.STPointN(@ptCounter).STX, 38, 8))) + ', ' + LTRIM(RTRIM(STR(@intRing.STPointN(@ptCounter).STY, 38, 8))) + '], '
                    SET @ptCounter -= 1
                END

                SET @geoJSON = LEFT(@geoJSON, LEN(@geoJSON) - 1) + ']'

                SET @ringCounter += 1
            END



            SET @geoJSON += '],'
            SET @gCounter += 1
        END

        SET @geoJSON = LEFT(@geoJSON, LEN(@geoJSON) - 1) + '] }'
        SET @handled = 1
    END






    IF (@handled = 0)
    BEGIN
        SET @geoJSON = '{"type": "' + @geom.STGeometryType() + '", "coordinates": []}'
    END




    RETURN @geoJSON



END

然后我可以像这样选择一个单独的 GeoJSON 对象：

    SELECT dbo.geomToGeoJSON(GEOMCOLNAME) FROM DB.gis.PARCEL WHERE PARCEL = 'R1525750900'

并得到一个看起来像的结果

    {
        "type": "Polygon",
        "coordinates": [
            [
                [-116.27593761, 43.62939598],
                [-116.27558219, 43.62939633],
                [-116.27558253, 43.62955520],
                [-116.27582493, 43.62955445],
                [-116.27582534, 43.62963010],
                [-116.27593893, 43.62962975],
                [-116.27593761, 43.62939598]
            ]
        ]
    }

或者我可以像这样将一整套对象打包到一个 FeatureCollection 中：

        DECLARE @GeoJSON VARCHAR(MAX)
        SET @GeoJSON = '{"type": "FeatureCollection", "features": ['

        SELECT
            @GeoJSON += '{"type": "Feature", "geometry": ' + sde_apps.dbo.geomToGeoJSON(SHAPE) + ', "properties": { "Parcel": "' + PARCEL + '"}},'
        FROM
            db.gis.PARCEL
        WHERE
            SUBNM LIKE @subnm


        SET @GeoJSON = LEFT(@GeoJSON, LEN(@GeoJSON) - 1) + ']}'

        SELECT
            @GeoJSON

查询性能取决于几何的复杂性和数量，但我通常在大约十分之二秒内得到结果。

我已经使用 MSDN 中的示例几何图形进行了验证，然后将生成的 GeoJSON 输入到http://geojsonlint.com/ 中。我知道这已经一年了，但我仍然有需求，我怀疑没有地图服务器的任何人都可以使用类似的东西在 Bing 地图上绘制图层等生成自己的简单地图服务器。

Answer 2

如果您有权访问 PostgreSQL/PostGIS，则可以使用ST_GeomFromText读取几何图形并将ST_AsGeoJSON几何图形保存为 GeoJSON：

SELECT ST_AsGeoJSON(ST_GeomFromText('POLYGON((455216.346127297 
 4288433.28426224,455203.386722146 4288427.76317716,455207.791765017
 4288417.51116228,455220.784166744 4288423.30230044,455216.346127297
 4288433.28426224))'));

，生成：

-------------------------------------------------------------------------------

 {"type":"Polygon","coordinates":[[[455216.346127297,4288433.28426224],
[455203.386722146,4288427.76317716],[455207.791765017,4288417.51116228],
[455220.784166744,4288423.30230044],[455216.346127297,4288433.28426224]]]}

    (1 row)