polyline creation - Creating one-sided buffers or parallel lines in PostGIS?

I'm looking for a way to create so-called one-sided buffers or parallel lines in PostGIS. Example: 1. buffer, 2. one-side, 3. both-sides

I've found some discussion on the mailing list from 2009 and information that it has been implemented in GEOS, but nothing about the current PostGIS status.

In case the function is not implemented yet, do you know any workarounds? Is it possible to cut off one side of a normal buffer?

Answer

Proper one-sided buffers were supposed to have landed in 1.5, but it looks to me that while the styles did land, sidedness didn't make it in. There is however a current patchset which exposes GEOSSingleSidedBuffer and performs the one-sided buffer as expected, under the name ST_OffsetCurve; see further background in ticket #413. In use:

select ST_AsText(ST_OffsetCurve(
ST_GeomFromText('LINESTRING(10 10,10 20, 20 20 )'),

1,'right', 'join=mitre mitre_limit=5.0'));
--------------
LINESTRING(20 19,11 19,11 10)