ST_Normalize() has different behavior with GEOS < 3.9.0 and => 3.9.0

[strk]

ST_Normalize('LINESTRING(2 8,2 2,8 2,8 8,2 8)'::geometry)

The above query gives a different result in GEOS-3.8 or earlier and GEOS-3.9 or later. In the first case (older GEOS) the LINESTRING is returned untouched, while in the second case (GEOS-3.9.0+) is returned changed in winding to become clockwise.

As ST_Normalize is used to avoid these kind of differences across versions this is, I think, and unwanted behavioural change.

I do understand we might want to ensure a winding direction for closed Linestrings, but maybe it should be a user choice to decide whether or not to do that, given not all GEOS versions support it ? Maybe we should do the reordering in PostGIS to be immune of behavioural changes

[strk]

Filed upstream ticket: ​https://trac.osgeo.org/geos/ticket/1109

[strk]

If we consider the "untouched linestring" as a GEOS bug, we could easily workaround the bug by (in case GEOS < 3.9.0) creating a Polygon out of a closed linestring, normalizing it and picking its boundary after normalization. I've tested this to work effectively on my client code.

[strk]

Reference: ​https://gitlab.com/nibioopensource/pgtopo_update_sql/-/merge_requests/80/diffs#bcb4364a38698228ee4bd479fb131e15aeab85b8_0_21