使用 PostgreSQL 从 Well Known Text 创建 GeoJSON 输出

Question

我有 wkt 数据，我正在尝试在 PostgreSQL 中创建一个 JSON 输出。

我知道有一个函数 ST_AsGeoJSON (https://postgis.net/docs/ST_AsGeoJSON.html) 创建了例如：

SELECT ST_AsGeoJSON('LINESTRING(77.29 29.07,77.42 29.26,77.27 29.31,77.29 29.07)');

Output:
{"type":"LineString","coordinates":[[77.29,29.07],[77.42,29.26],[77.27,29.31],[77.29,29.07]]}

但是，我希望创建如下所示的输出：

{"type":"LineString","coordinates":[{"x":77.29,"y":29.07},{"x":77.42,"y":29.26},{"x":77.27,"y":29.31},{"x":77.29,"y":29.07}]}

请注意，我正在寻找适用于所有类型几何对象的通用解决方案。谢谢

Answer 1

您可以使用正则表达式将 [a,b] 替换为 {"x":a,"y":b}，如下所示：

CREATE OR REPLACE FUNCTION ST_AsCustomGeoJson(geom geometry)
RETURNS TEXT
AS 
$$
    -- Look for each coordinate and replace [number_a,number_b] with {"x":number_a,"y":number_b}
    SELECT REGEXP_REPLACE(
        ST_AsGeoJSON(geom),
        '\[(-?[0-9]+\.?[0-9]*)(e\+[0-9]+)?,(-?[0-9]+\.?[0-9]*)(e\+[0-9]+)?\]',
        '{"x":,"y":}',
        'g');
$$
LANGUAGE SQL IMMUTABLE STRICT PARALLEL SAFE;

使用新函数，您得到了预期的响应：

# Select ST_AsCustomGeoJson('LINESTRING(77.29 29.07,77.42 29.26,77.27 29.31,77.29 29.07)'::geometry);                                              st_ascustomgeojson                                               
---------------------------------------------------------------------------------------------------------------
 {"type":"LineString","coordinates":[{x:77.29,y:29.07},{x:77.42,y:29.26},{x:77.27,y:29.31},{x:77.29,y:29.07}]}
(1 row)

它也应该适用于其他几何类型：

# Select ST_AsCustomGeoJson('POLYGON((0 0, 0 10, 10 10, 10 0, 0 0),(1 1, 1 9, 9 9, 9 1, 1 1))'::geometry);
                                                                                   st_ascustomgeojson                                                                                   
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 {"type":"Polygon","coordinates":[[{"x":0,"y":0},{"x":0,"y":10},{"x":10,"y":10},{"x":10,"y":0},{"x":0,"y":0}],[{"x":1,"y":1},{"x":1,"y":9},{"x":9,"y":9},{"x":9,"y":1},{"x":1,"y":1}]]}
(1 row)

# Select ST_AsCustomGeoJson('LINESTRING(3e20 3e20, 1e100 40)'::geometry);
                               st_ascustomgeojson                                
---------------------------------------------------------------------------------
 {"type":"LineString","coordinates":[{"x":3e+20,"y":3e+20},{"x":1e+100,"y":40}]}
(1 row)

连几何集合：

# Select ST_AsCustomGeoJson('GEOMETRYCOLLECTION (POINT(-1 0), LINESTRING(4 4,5 5))');
                                                                      st_ascustomgeojson                                     

-----------------------------------------------------------------------------------------------------------------------------
---------------------------------
 {"type":"GeometryCollection","geometries":[{"type":"Point","coordinates":{"x":-1,"y":0}},{"type":"LineString","coordinates":
[{"x":4,"y":4},{"x":5,"y":5}]}]}

Answer 2

我相信一个简单的循环 jsonb_build_obejct over a result set from ST_DumpPoints would suffice. If you also want to apply this function in multipart geometries, you have to build another loop to extract all geometries beforehand using ST_Dump:

CREATE OR REPLACE FUNCTION generate_custom_geojson(g GEOMETRY)
RETURNS json AS $$
DECLARE
  j geometry;
  i geometry;
  coords jsonb[] := '{}';
  coords_multi jsonb[] := '{}';
BEGIN     
  FOR j IN SELECT (ST_Dump(g)).geom LOOP
    FOR i IN SELECT (ST_DumpPoints(j)).geom LOOP
      coords := coords || jsonb_build_object('x',ST_X(i),'y',ST_Y(i)); 
    END LOOP;
    IF ST_NumGeometries(g)=1 THEN
      coords_multi := coords; 
    ELSE 
      coords_multi := coords_multi || jsonb_agg(coords); 
    END IF; 
  END LOOP;
  RETURN json_build_object('type',replace(ST_GeometryType(g),'ST_',''),
                           'coordinates',coords_multi);
END;
$$ LANGUAGE plpgsql;

此函数简单地提取给定几何体的所有点并将它们放入数组中 - 使用 || 附加。该数组稍后用于创建 coordinates 组 x,y 对。使用 ST_GeometryType.

提取几何类型

测试：

WITH j (g) AS (
  VALUES ('LINESTRING(77.29 29.07,77.42 29.26,77.27 29.31,77.29 29.07)'),
         ('POLYGON ((30 10, 40 40, 20 40, 10 20, 30 10))'),
         ('MULTILINESTRING ((10 10, 20 20, 10 40),(40 40, 30 30, 40 20, 30 10))'),
         ('MULTIPOLYGON (((30 20, 45 40, 10 40, 30 20)),((15 5, 40 10, 10 20, 5 10, 15 5)))'),
         ('MULTIPOINT (10 40, 40 30, 20 20, 30 10)')
)
SELECT generate_custom_geojson(g) FROM j;

---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 {"type" : "LineString", "coordinates" : [{"x": 77.29, "y": 29.07},{"x": 77.42, "y": 29.26},{"x": 77.27, "y": 29.31},{"x": 77.29, "y": 29.07}]}
 {"type" : "Polygon", "coordinates" : [{"x": 30, "y": 10},{"x": 40, "y": 40},{"x": 20, "y": 40},{"x": 10, "y": 20},{"x": 30, "y": 10}]}
 {"type" : "MultiLineString", "coordinates" : [[[{"x": 10, "y": 10}, {"x": 20, "y": 20}, {"x": 10, "y": 40}]],[[{"x": 10, "y": 10}, {"x": 20, "y": 20}, {"x": 10, "y": 40}, {"x": 40, "y": 40}, {"x": 30, "y": 30}, {"x": 40, "y": 20}, {"x": 30, "y": 10}]]]}
 {"type" : "MultiPolygon", "coordinates" : [[[{"x": 30, "y": 20}, {"x": 45, "y": 40}, {"x": 10, "y": 40}, {"x": 30, "y": 20}]],[[{"x": 30, "y": 20}, {"x": 45, "y": 40}, {"x": 10, "y": 40}, {"x": 30, "y": 20}, {"x": 15, "y": 5}, {"x": 40, "y": 10}, {"x": 10, "y": 20}, {"x": 5, "y": 10}, {"x": 15, "y": 5}]]]}
 {"type" : "MultiPoint", "coordinates" : [[[{"x": 10, "y": 40}]],[[{"x": 10, "y": 40}, {"x": 40, "y": 30}]],[[{"x": 10, "y": 40}, {"x": 40, "y": 30}, {"x": 20, "y": 20}]],[[{"x": 10, "y": 40}, {"x": 40, "y": 30}, {"x": 20, "y": 20}, {"x": 30, "y": 10}]]]}
(5 Zeilen)

使用 PostgreSQL 从 Well Known Text 创建 GeoJSON 输出

Creating GeoJSON output from Well Known Text with PostgreSQL

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