I've found the solution : it's the export routine pgsql2shp that
needs a table with at least 3 variables : a primary key (gid in my
table), a geometry (the_geom in my table) and a third variable
whatever is this variable in order to produce a dbf file that is not
empty.
With the following code, it's ok :
create table temp as select r.gid, ST_Difference
(r.the_geom,i.the_geom) as the_geom,area2D(ST_Difference
(r.the_geom,i.the_geom)) as area from recouv as r, recouv as i where
i.gid=2 and r.gid=1;
ALTER TABLE temp ADD PRIMARY KEY (gID);
\q
pgsql2shp -f ext.shp conversion 'select * from matable2'
Thanks.
Ghislain.
Le 12 mars 08 à 15:15, Obe, Regina a écrit :
Could be your export routine then. I don't think ' is legal. Need
to use double-quotes (or at least on windows) for the SQL. You can
also leave out the .shp although I guess its harmless.
Try
pgsql2shp -f ext conversion "select * from matable2"
Hope that helps,
Regina
From: [EMAIL PROTECTED] [mailto:postgis-
[EMAIL PROTECTED] On Behalf Of Ghislain Geniaux
Sent: Wednesday, March 12, 2008 8:47 AM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] problem creating and exporting a
polygon withholeusing pgsql2shp
Thanks for your answer Regina,
but ST_Difference does not solve the problem :
ST_Difference and ST_Symdifference give the same polygon but the
export by pgsql2shp failled.
conversion=# create table temp as
conversion-# select r.gid, ST_Difference(r.the_geom,i.the_geom) as
the_geom from recouv as r, recouv as i where i.gid=2 and r.gid=1;
SELECT
conversion=# ALTER TABLE temp ADD PRIMARY KEY (gID);
NOTICE: ALTER TABLE / ADD PRIMARY KEY will create implicit index
"temp_pkey" for table "temp"
ALTER TABLE
conversion=# SELECT geometrytype(the_geom), Nrings(the_geom), area2d
(the_geom) from temp;
geometrytype | nrings | area2d
--------------+--------+------------------
POLYGON | 2 | 2177713.02017212
(1 row)
conversion=# create table temp as
conversion-# select r.gid, ST_symDifference(r.the_geom,i.the_geom)
as the_geom from recouv as r, recouv as i where i.gid=2 and r.gid=1;
SELECT
conversion=# ALTER TABLE temp ADD PRIMARY KEY (gID);
NOTICE: ALTER TABLE / ADD PRIMARY KEY will create implicit index
"temp_pkey" for table "temp"
ALTER TABLE
conversion=# SELECT geometrytype(the_geom), Nrings(the_geom), area2d
(the_geom) from temp;
geometrytype | nrings | area2d
--------------+--------+------------------
POLYGON | 2 | 2177713.02017212
(1 row)
The two polygons are goods and well displayed in QGIS but exported
shapefiles are empty or corrupted.
Le 12 mars 08 à 12:51, Obe, Regina a écrit :
I'm guessing your result may be a Geometrycollection which ESRI
shape has no clue what to do with.
If I understand you correctly, I think you really should be using
ST_Difference instead of ST_SymDifference.
So ST_Difference(polygon2, polygon1) - will give you that portion
of polygon2 which does not intersect with polygon1 which would
give you a polygon with polygon1 removed (a doughnut so to speak).
The ST_Symdifference will give you that portion of polygon2 not in
polygon1 + polygon1 not in polygon2 = the holed polygon you want +
an empty geometry collection -> a geometry collection if taken
strictly.
I'm not sure if PostGIS will throw out the second part (the empty
collection) - and at anyrate is a waste of processing power to
even compute it.
Hope that helps,
Regina
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf
Of Ghislain Geniaux
Sent: Wednesday, March 12, 2008 6:29 AM
To: [email protected]
Subject: [postgis-users] problem creating and exporting a polygon
with holeusing pgsql2shp
Using a postgis table with Two polygons, in which polygon 1
entirely contained in polygon 2, I've create a new polygon with a
hole using :
------
create table matable2 as
select r.gid, area(symdifference(r.the_geom,i.the_geom)) as area,
(symdifference(r.the_geom,i.the_geom)) as the_geom from matable as
r, matable as i where i.gid=2 and r.gid=1;
ALTER TABLE matable2 ADD PRIMARY KEY (GID);
\q
pgsql2shp -f ext.shp conversion 'select * from matable2'
-----
Area is correct, display of the polygon in QGIS is also correct,
but the export by pgsl2shp produce an empty shapefile.
How to deal with this problem?
------------------------------------------
Geniaux Ghislain
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Geniaux Ghislain
INRA SAD Ecodéveloppement
Site Agroparc
Domaine St Paul
84914 Avignon Cedex 9
Tél : 04 32 72 25 64
Fax : 04 32 72 25 62
_______________________________________________
postgis-users mailing list
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------------------------------------------
Geniaux Ghislain
INRA SAD Ecodéveloppement
Site Agroparc
Domaine St Paul
84914 Avignon Cedex 9
Tél : 04 32 72 25 64
Fax : 04 32 72 25 62
_______________________________________________
postgis-users mailing list
[email protected]
http://postgis.refractions.net/mailman/listinfo/postgis-users
