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Help on Posgis

Postgis book ​http://www.postgis.fr/book/print/156#413413413
​http://postgis.refractions.net/documentation/manual-1.5/
url: ​http://www.bostongis.com/?content_name=postgis_tut01#20

Projections

2154	RGF93_Lambert_93
3035	ETRS89
27572	LambertII

I would like to create a postgis table from a postgres table with x y

The data are in lambert II étendu

select * from bdmap.spatial_ref_sys where srtext like '%Lambert%' and srtext like '%II%' 

seems to be 27572

SELECT AddGeometryColumn('bdmap', 'station','the_geom', 27572,'POINT',2) 

from Laurent

UPDATE bdmap
   SET the_geom=PointFromText('POINT(' || st_abcisse || ' ' || st_ordonnee || ')',27572);

I've got a message from Qgis saying that I'm not allowed to use a table without int4 primary key or OID

ALTER TABLE bdmap.station SET WITH OIDS;

Here we add a validity constraint

ALTER TABLE bdmap.station ADD CONSTRAINT geometry_valid_check CHECK (isvalid(the_geom)); 

To transform the coordinate towards the CCM To figure out the srid of a data go to the table geometry_column, there is on line per table

SELECT ST_Transform(the_geom,3035) FROM bdmap.station;

Building an index (very quick with this table)

CREATE INDEX indexStations ON bdmap.station
  USING GIST ( the_geom GIST_GEOMETRY_OPS ); 

​http://www.postgis.fr/documentation/debian/postgis-1.1.2/html/ch02.html#id2499646 Usefull functions in postgis, they take as argument a geom

• Area2d()
• geometrytype()
• Distance(A,B)
• WithIn(A,B) A inside B
• Min()
• Distance()

Reprojecting / snapping point-geometries onto a given line-geometry using PostGIS ​http://62.160.92.241:8066/trac/wiki/CookBook%20Postgis?action=edit

SELECT ST_Line_Interpolate_Point(
		line_to_project_onto.the_geom,
		ST_Line_Locate_Point(
			line_to_project_onto.the_geom,
			points_to_project_onto_line.the_geom
		)
	)
FROM line_to_project_onto, points_to_project_onto_line;

which translates into

SELECT ST_Line_Interpolate_Point(
		riversegments.the_geom,
		ST_Line_Locate_Point(
			riversegments.the_geom,
			stationsp2.the_geom
		)
	)
FROM stationsp2, riversegments;

geometry columns

​http://postgis.refractions.net/docs/ch04.html#spatial_ref_sys

4.3.3. Creating a Spatial Table

Creating a table with spatial data is done in two stages:

• Create a normal non-spatial table.

For example: CREATE TABLE ROADS_GEOM ( ID int4, NAME varchar(25) )

• Add a spatial column to the table using the OpenGIS AddGeometryColumn function.

The syntax is:

      AddGeometryColumn(
        <schema_name>,
        <table_name>,
        <column_name>,
        <srid>,
        <type>,
        <dimension>
      )

Or, using current schema:

      AddGeometryColumn(
        <table_name>,
        <column_name>,
        <srid>,
        <type>,
        <dimension>
      )

      Example1: SELECT AddGeometryColumn('public', 'roads_geom', 'geom', 423, 'LINESTRING', 2)

      Example2: SELECT AddGeometryColumn( 'roads_geom', 'geom', 423, 'LINESTRING', 2)

Here is an example of SQL used to create a table and add a spatial column (assuming that an SRID of 128 exists already):

CREATE TABLE parks (
  park_id    INTEGER,
  park_name  VARCHAR,
  park_date  DATE,
  park_type  VARCHAR
);
SELECT AddGeometryColumn('parks', 'park_geom', 128, 'MULTIPOLYGON', 2 );

Here is another example, using the generic "geometry" type and the undefined SRID value of -1:

CREATE TABLE roads (
  road_id INTEGER,
  road_name VARCHAR
);
SELECT AddGeometryColumn( 'roads', 'roads_geom', -1, 'GEOMETRY', 3 );

4.3.4. Manually Registering Geometry Columns in geometry_columns

The AddGeometryColumn() approach creates a geometry column and also registers the new column in the geometry_columns table. If your software utilizes geometry_columns, then any geometry columns you need to query by must be registered in this table. Two of the cases where you want a geometry column to be registered in the geometry_columns table, but you can't use AddGeometryColumn, is in the case of SQL Views and bulk inserts. For these cases, you must register the column in the geometry_columns table manually. Below is a simple script to do that.

• Lets say you have a view created like this

  CREATE VIEW  public.vwmytablemercator AS
  	SELECT gid, ST_Transform(the_geom,3395) As the_geom, f_name
  	FROM public.mytable;
  

• To register this table in AddGeometry columns - do the following

  INSERT INTO geometry_columns(f_table_catalog, f_table_schema, f_table_name, f_geometry_column, coord_dimension, srid, "type")
  SELECT '', 'public', 'vwmytablemercator', 'the_geom', ST_CoordDim(the_geom), ST_SRID(the_geom), GeometryType(the_geom)
  FROM public.vwmytablemercator LIMIT 1;
  

• Lets say you created a derivative table by doing a bulk insert

  SELECT poi.gid, poi.the_geom, citybounds.city_name
  INTO myschema.myspecialpois
  FROM poi INNER JOIN citybounds ON ST_Intersects(citybounds.the_geom, poi.the_geom);
  

• Create index on new table

  CREATE INDEX idx_myschema_myspecialpois_geom_gist
    ON myschema.myspecialpois USING gist(the_geom);
  

• To manually register this new table's geometry column in geometry_columns we do the same thing as with view

  INSERT INTO geometry_columns(f_table_catalog, f_table_schema, f_table_name, f_geometry_column, coord_dimension, srid, "type")
  SELECT '', 'myschema', 'myspecialpois', 'the_geom', ST_CoordDim(the_geom), ST_SRID(the_geom), GeometryType(the_geom)
  FROM public.myschema.myspecialpois LIMIT 1;
  

Get SRID from a column

An example with ROE

select SRID (ref_position_locale) FROM geobs.obstacle_referentiel

Other usefull functions (memo)

select ST_SetSRID().

select Probe_Geometry_Columns() 
Scans all tables with PostGIS geometry constraints and adds them to the geometry_columns table if they are not already there. Also give stats on the number of inserts, already present, or possibly obsolete columns.