That's a bug in JTS, alright. Thanks to Michael for finding it, and Sandro
for identifying the problem. I'll look at fixing this ASAP.
On Tue, Jan 14, 2014 at 1:36 AM, Sandro Santilli <[email protected]> wrote:
> On Mon, Jan 13, 2014 at 12:41:37PM -0800, Michael Watts wrote:
> > I'm not sure if this is a PostGIS issue, a JTS issue, or an issue at all
> --
> > but, below, JTS produces a WKB that is not parseable (via ST_GeomFromWKB)
> > by Postgis -- it is the JTS wkb-representation of an empty polygon.
> >
> > ===============================
> >
> > (1) Get WKB from PostGIS
> >
> > gis=> select ST_GEOMFromText('POLYGON EMPTY');
> > st_geomfromtext
> > --------------------
> > 010300000000000000
> > (1 row)
> >
> > (2) Write to JTS, and read back.
> >
> > WKBWriter writer = new WKBWriter();
> > WKBReader reader = new WKBReader();
> >
> > // 010300000000000000
> > byte[] fromPostgis = {1, 3, 0, 0, 0, 0, 0, 0}; // little-endian,
> polygon, 0
> > rings
> >
> > // 00000000030000000100000000
> > byte[] throughJTS = writer.write(reader.read(fromPostgis)); // big
> endian,
> > polygon, 1 ring, 0 points
> >
> > (3) Try to write back to PostGIS
> >
> > gis=> select ST_GeomFromWKB(E'\\x00000000030000000100000000');
> > ERROR: Polygon must have at least four points in each ring
> >
> > ================================
> >
> > JTS-Version = 1.13
> > POSTGIS="2.1.0 r11822"
>
> PostGIS binary version for an empty polygon is different:
>
> strk=# select ST_AsBinary('POLYGON EMPTY'::geometry, 'ndr');
> st_asbinary
> ----------------------
> \x010300000000000000
> (1 row)
>
> strk=# select ST_AsBinary('POLYGON EMPTY'::geometry, 'xdr');
> st_asbinary
> ----------------------
> \x000000000300000000
> (1 row)
>
> That is, a polygon with NO rings, whereas it looks like JTS version
> is a polygon with 1 empty ring ?
>
> --strk;
>
>
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