PostGeoSQL/ST_RoadAxis at main · CM-FOGS/PostGeoSQL · GitHub

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DROP FUNCTION IF EXISTS ST_RoadAxis(
    geom GEOMETRY,
    n integer)

CREATE OR REPLACE FUNCTION ST_RoadAxis(
    geom GEOMETRY,
    n integer)
RETURNS GEOMETRY AS
$BODY$
      WITH
          geodata AS (SELECT (ST_Dump(geom)).geom),
          left_line AS (SELECT (ST_Dump(geom)).geom geom FROM geodata LIMIT 1),
          right_line AS (SELECT (a.geom) geom FROM geodata a WHERE NOT EXISTS (SELECT 1 FROM left_line b WHERE ST_Intersects(a.geom, b.geom))),
          intervals AS (SELECT generate_series (0, n) steps),
          lineinterpnt AS (SELECT steps AS stp, ST_LineInterpolatePoint(geom, steps/(SELECT count(steps)::float-1 FROM intervals)) geom FROM left_line, intervals GROUP BY intervals.steps, geom ORDER BY intervals.steps),
          sleepers AS (SELECT DISTINCT stp, ST_ShortestLine(a.geom, b.geom) geom FROM lineinterpnt a CROSS JOIN LATERAL (SELECT (geom) geom FROM right_line) b ORDER BY stp)
          SELECT ST_MakeLine(geom) geom FROM (SELECT stp, ST_LineInterpolatePoint(geom, 0.5) geom FROM sleepers ORDER BY stp) foo;
$BODY$
LANGUAGE SQL

SELECT ST_RoadAxis(ST_Union(geom), 300) geom FROM parallel_street

*experimental function*