Create a middle line through a polygon path using postgis

I'm trying to create a middle line through a polygon path but having problems, now i'm totally lost how to do it. Can anyone help to achieve this goal ?

Solution

ST_ApproximateMedialAxis might be what you're looking for.

This PostGIS function can be installed with the extension postgis_sfcgal:

CREATE EXTENSION postgis_sfcgal

Data Sample:

CREATE TABLE t (geom GEOMETRY);
INSERT INTO t VALUES ('POLYGON((-4.689807593822478 54.20411976258862,-4.68751162290573 54.20415427666532,-4.686465561389922 54.20414172609529,-4.685768187046051 54.20414800138079,-4.685280025005341 54.20414486373812,-4.685070812702178 54.204126037877415,-4.685092270374298 54.2040538719985,-4.685854017734527 54.204078973188075,-4.687039554119109 54.20407583554021,-4.688123166561126 54.204082110835685,-4.689078032970428 54.2040601472973,-4.689936339855194 54.20403818374726,-4.689807593822478 54.20411976258862))');

Query:

SELECT ST_ASText(ST_ApproximateMedialAxis(geom)) FROM t;
--------------------------------------------------------
MULTILINESTRING((-4.68993633985519 54.2040381837473,-4.68979598869017 54.2040808603332),(-4.68812343743121 54.2041135944836,-4.68907889005644 54.2040954248621),(-4.68812343743121 54.2041135944836,-4.68751156547988 54.2041164214432),(-4.68646560965613 54.2041095395079,-4.6858535007301 54.2041131034922),(-4.68646560965613 54.2041095395079,-4.68703949691079 54.2041122226661),(-4.6858535007301 54.2041131034922,-4.68576814087419 54.2041120816007),(-4.68907889005644 54.2040954248621,-4.68979598869017 54.2040808603332),(-4.68576814087419 54.2041120816007,-4.68528206303828 54.2041025125126),(-4.68703949691079 54.2041122226661,-4.68751156547988 54.2041164214432),(-4.68512015518242 54.2040925683677,-4.68528206303828 54.2041025125126))
(1 Zeile)

Depending on your use case, another option would be ST_StraightSkeleton:

SELECT ST_ASText(ST_StraightSkeleton(geom)) FROM t;
-----------------------------------------------------
MULTILINESTRING((-4.68980759382248 54.2041197625886,-4.68979598869017 54.2040808603332),(-4.68993633985519 54.2040381837473,-4.68979598869017 54.2040808603332),(-4.68907803297043 54.2040601472973,-4.68907889005644 54.2040954248621),(-4.68812316656113 54.2040821108357,-4.68812343743121 54.2041135944836),(-4.68703955411911 54.2040758355402,-4.68703949691079 54.2041122226661),(-4.68585401773453 54.2040789731881,-4.6858535007301 54.2041131034922),(-4.6850922703743 54.2040538719985,-4.68512015518242 54.2040925683677),(-4.68507081270218 54.2041260378774,-4.68512015518242 54.2040925683677),(-4.68528002500534 54.2041448637381,-4.68528206303828 54.2041025125126),(-4.68576818704605 54.2041480013808,-4.68576814087419 54.2041120816007),(-4.68646556138992 54.2041417260953,-4.68646560965613 54.2041095395079),(-4.68751162290573 54.2041542766653,-4.68751156547988 54.2041164214432),(-4.68812343743121 54.2041135944836,-4.68907889005644 54.2040954248621),(-4.68812343743121 54.2041135944836,-4.68751156547988 54.2041164214432),(-4.68646560965613 54.2041095395079,-4.6858535007301 54.2041131034922),(-4.68646560965613 54.2041095395079,-4.68703949691079 54.2041122226661),(-4.6858535007301 54.2041131034922,-4.68576814087419 54.2041120816007),(-4.68907889005644 54.2040954248621,-4.68979598869017 54.2040808603332),(-4.68576814087419 54.2041120816007,-4.68528206303828 54.2041025125126),(-4.68703949691079 54.2041122226661,-4.68751156547988 54.2041164214432),(-4.68512015518242 54.2040925683677,-4.68528206303828 54.2041025125126))
(1 Zeile)