ST_SimplifyPreserveTopology creates invalid geometries [fixed by GEOS-3.3.4]

[strk]

When simplifying a closed linestring by a tolerance higher than the max extent dimension such closed linestring becomes formed by 2 equal points, which makes it invalid.

I belive the whole point of preserving topology should be preventing such occurrences.

[strk]

Example:

=# select ST_AsText(geom), ST_IsValid(geom), st_astext(ST_SimplifyPreserveTopology(geom,200)), ST_IsValid(ST_SimplifyPreserveTopology(geom, 200)) from ( select 'LINESTRING(0 0, 5 0, 5 5, 0 0)'::geometry as geom ) as f;
NOTICE:  Too few points in geometry component at or near point 0 0
-[ RECORD 1 ]---------------------------
st_astext  | LINESTRING(0 0,5 0,5 5,0 0)
st_isvalid | t
st_astext  | LINESTRING(0 0,0 0)
st_isvalid | f

[strk]

This is likely a JTS bug

[strk]

See ​http://trac.osgeo.org/geos/ticket/508

[pramsey]

A GEOS bug, not a blocker for 2.0 (it's not new, it's been around forever), so I'm pushing forward.

[strk]

Martin fixed this in JTS. See the GEOS part of this here: ​http://trac.osgeo.org/geos/ticket/510

[strk]

Nothing to do here, it's fixed by upgrading GEOS to 3.3.4+