Le blog de Jean David TECHER, un Réunionnais à Saint-Priest/Lyon

By default when you want to have the postgis.pdf taken from the source, you have to install fo or db2pdf. However, you can use a tool like dblatex. The solution is available at http://dblatex.sourceforge.net/. This project is maintaned by Benoît Guillon (a French guy too like me ).

The main goal is as followed

Install dblatex >=0.2.7

First of all you need dblatex. Please read the instructions taken from the dblatex's site. You need to have python, latex and so on..

When you're ready. It is time to install

./setup.py install

Building the pdf doc from PostGIS

1. Download the sources from svn

   wget http://www.postgis.org/postgis-svn.tar.gz

2. Untar the sources

   tar xvf postgis-svn.tar.gz

3. Go to postgis directory, run configure and go to doc directory

   ./configure && cd doc && make

4. The file reference.xml must be change. We have to replace the term entry by listitem before using dbaltex

   cp reference.xml reference.xml.orig; cat reference.xml.orig |sed -e "s:term:listitem:g" > reference.xml

5. It's time to use dblatex. Here is the command and the output

   root@olivia:/mnt/sources/tmp/postgis-svn/doc# dblatex -T native -t pdf -o postgis-svn-1.4.0.pdf -I "$PWD/html" postgis-out.xml 
   Build the listings...
   XSLT stylesheets DocBook -  LaTeX 2e (0.2.9)
   ===================================================
   convert "/mnt/sources/tmp/postgis-svn/doc/html/images/st_crosses-math.gif" fig0.pdf
   convert "/mnt/sources/tmp/postgis-svn/doc/html/images/st_crosses01.gif" fig1.pdf
   convert "/mnt/sources/tmp/postgis-svn/doc/html/images/st_crosses02.gif" fig2.pdf
   convert "/mnt/sources/tmp/postgis-svn/doc/html/images/st_crosses03.gif" fig3.pdf
   convert "/mnt/sources/tmp/postgis-svn/doc/html/images/st_crosses04.gif" fig4.pdf
   convert "/mnt/sources/tmp/postgis-svn/doc/html/images/st_touches-math.gif" fig5.pdf
   Build postgis-out.pdf
   This is pdfeTeX, Version 3.141592-1.30.5-2.2 (Web2C 7.5.5)
   entering extended mode
   This is pdfeTeX, Version 3.141592-1.30.5-2.2 (Web2C 7.5.5)
   entering extended mode
   'postgis-svn-1.4.0.pdf' successfully built

Here is the final PDF http://www.davidgis.fr/download/postgis-svn-1.4.0.pdf...Beautifull isn't it ???

On a la table suivante

www_log=# create table test(id integer,name text);
CREATE TABLE
www_log=# insert into test select generate_series(1,10),'toto';
INSERT 0 10
www_log=# select * from test ;
 id | name 
----+------
  1 | toto
  2 | toto
  3 | toto
  4 | toto
  5 | toto
  6 | toto
  7 | toto
  8 | toto
  9 | toto
 10 | toto
(10 lignes)

On va mettre tout ça à jour. Quand id est pair name vaut tata ,yoyo sinon.

www_log=# UPDATE test set name=(case when id%2=0 then 'tata' else 'yoyo' end);
UPDATE 10
www_log=# select * from test ;
 id | name 
----+------
  1 | yoyo
  2 | tata
  3 | yoyo
  4 | tata
  5 | yoyo
  6 | tata
  7 | yoyo
  8 | tata
  9 | yoyo
 10 | tata
(10 lignes)

L'annonce a été publiée hier. Elle se trouve ici. Je ne fais que relayer l'information.

Il faut penser à s'inscrire comme stipulé pour poster un message sur le nouveau forum.

ST_Numrings() est une fonctionnalité qui s'avère bien util. Un petit exemple pour la route

On va commencer par créer une table test qui contiendra le dit polygon

create table test(id serial,the_geom geometry);

Faisons notre insertion

insert into test(the_geom) values  ('POLYGON (( 1 1, 1 7, 7 7, 7 1, 1 1 ),
				   ( 2 3, 4 3, 4 5, 2 5, 2 3 ),
				( 5 5, 6 5, 6 6, 5 6, 5 5 ),
				(4.51 1.42,6.31 1.34,6.78 4.86,4.57 4.13,4.51 1.42),
				(1.20 5.36,4.62 5.63,4.86 6.84,1.20 5.36))'::geometry);

Le polygon ressemblera à ceci

Déjà grâce à ST_Numrings(), nous avons le descriptif suivant

testgis=# select (st_dumprings(the_geom)).path[1] as id ,astext((st_dumprings(the_geom)).geom) as geom from test;
 id |                             geom                             
----+--------------------------------------------------------------
  0 | POLYGON((1 1,1 7,7 7,7 1,1 1))
  1 | POLYGON((2 3,4 3,4 5,2 5,2 3))
  2 | POLYGON((5 5,6 5,6 6,5 6,5 5))
  3 | POLYGON((4.51 1.42,6.31 1.34,6.78 4.86,4.57 4.13,4.51 1.42))
  4 | POLYGON((1.2 5.36,4.62 5.63,4.86 6.84,1.2 5.36))
(5 lignes)

On comprend ici que le POLYGON contenant est le premier i.e. POLYGON((1 1,1 7,7 7,7 1,1 1)). Les autres étant les trous du polygon.

Pour notre problème, il suffira de faire

testgis=# select astext(foo.geom),area(foo.geom) from (select (st_dumprings(the_geom)).geom as geom from test) as foo,test 
where not contains(foo.geom,test.the_geom) order by 2 desc;
                            astext                            |  area   
--------------------------------------------------------------+---------
 POLYGON((4.51 1.42,6.31 1.34,6.78 4.86,4.57 4.13,4.51 1.42)) | 6.15945
 POLYGON((2 3,4 3,4 5,2 5,2 3))                               |       4
 POLYGON((1.2 5.36,4.62 5.63,4.86 6.84,1.2 5.36))             |  2.0367
 POLYGON((5 5,6 5,6 6,5 6,5 5))                               |       1
(4 lignes)

Plus simplement on peut aussi proposer

testgis=# select astext(foo.geom) from (select (st_dumprings(the_geom)).geom as geom from test) as foo,test
 where not contains(foo.geom,test.the_geom) order by area(foo.geom) desc;
                            astext                            
--------------------------------------------------------------
 POLYGON((4.51 1.42,6.31 1.34,6.78 4.86,4.57 4.13,4.51 1.42))
 POLYGON((2 3,4 3,4 5,2 5,2 3))
 POLYGON((1.2 5.36,4.62 5.63,4.86 6.84,1.2 5.36))
 POLYGON((5 5,6 5,6 6,5 6,5 5))
(4 lignes)

Ordre des troux rangés par surface décroissante