No. ST_AsText() has it places, but as you've seen, it does not give you
an accurate representation of your geometries. It is for this reason
that PostGIS moved away from the textual representation of geometries to
binary way back in release 1.0.0. Prior to this release, pg_dump would
dump a database using the textual form and was prone to coordinate
shifting and precision loss. There's more info on this canonical form if
you search the postgis-users and postgis-devel archives.
Recommendation: use ST_AsEWKB(), or ST_AsBinary(), or ST_AsHEXEWKB() if
you ever plan on editing your geometries - ie through JDBC.
Alternatively, you could use ST_AsText(), but it would be a good idea to
couple it closely with ST_Snaptogrid() (ie. by calling it after every
geometry edit, or by placing a rule or trigger on your tables).
Cheers,
Kevin
Andreas Neumann wrote:
Indeed - this ST_SnapToGrid() does the trick - and explains why
ST_Polygonize failed. I wonder if there is a way to see these very slight
inaccuracies with "ST_AsText()". In my case ST_AsText() only returned
three digits after the comma (that's why I assumed the start/end points
are actually the same), not the 10 digits you mention below. Is there any
trick to tell ST_AsText() to be more accurate?
Thanks again,
Andreas
This is not a bug. It looks like your linestrings are not properly noded.
IE. on your line in question, the end node is POINT (697787.741
247263.451), but the other two lines are noded at POINT
(697787.7410000002 247263.451).
Try using snaptogrid().
SELECT geom AS the_geom
FROM ST_Dump((
SELECT ST_Polygonize(ST_SnapToGrid(the_geom, 0.001)) AS geom
FROM admin.plz));
Cheers,
-------------
Kevin Neufeld
Software Developer
Refractions Research Inc.
300-1207 Douglas St.
Victoria, B.C., V8W 2E7
Phone: (250) 383-3022
Email: [EMAIL PROTECTED]
Andreas Neumann wrote:
Hello,
I have a linenetwork with 15 LINESTRING() elements. I am using
ST_POLYGONIZE() to create new POLYGON() elements. I'd expect to get 6
polygons, but ST_POLYGONIZE() creates only 5 polygons. To make sure that
my data is ok, I selected all start and endpoints of the LINESTRING()s
and
made sure that every start/endpoint of a LINESTRING() has two
counterparts, which is the case.
This looks like a bug to me. I would appreciate if someone else could a
look at my data. Attached is the dump of the table and a screenshot of
the
line-network. If you load the dump, you might want to replace the owners
with your own userid. In the screenshot, one line is marked as green.
This
is the line that is ignored by the ST_Polygonize() command.
I used
SELECT geom AS the_geom FROM ST_Dump((SELECT ST_Polygonize(the_geom) AS
geom FROM admin.plz));
as the SQL query.
I'd appreciate any help on my problem, resp. an answer if this might be
a
bug or not.
Thank you,
Andreas
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