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PostGIS - Geographic Information Systems Extensions to PostgreSQL ~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ VERSION: 0.6 (2001/09/20) MORE INFORMATION: http://postgis.refractions.net INTRODUCTION: This distribution contains a module which implements GIS simple features, ties the features to rtree indexing, and provides some basic functions for accessing and analyzing geographic data. Directory structure: ./ Core source code, makefiles and install directions. ./jdbc Extensions to the PostgreSQL JDBC drivers to support the GIS objects. ./doc Documentation on the code, objects and functions provided. ./loader A program to convert ESRI Shape files into SQL text suitable for uploading into a PostGIS/PostgreSQL database. ./examples Small programs which demonstrate ways of accessing GIS data. INSTALLATION: To install the module, move this directory to the "contrib" directory of your PostgreSQL source installation. Alternately, edit the "top_buildir" in the Makefile and point it at your PostgreSQL source tree. You must have a PostgreSQL source tree, and you must have run succesfully built and installed it for this to work. Then run: make make install PostGIS now requires the PL/pgSQL procedural language in order to operate correctly. To install PL/pgSQL, locate the plpgsql.so library in your PostgreSQL installation (usually in the 'lib' directory). Then run the following SQL commands in your database, replacing the plpgsql.so location with the correct one for your system: CREATE FUNCTION plpgsql_call_handler() RETURNS OPAQUE AS '/usr/local/pgsql/lib/plpgsql.so' LANGUAGE 'C'; CREATE TRUSTED PROCEDURAL LANGUAGE 'plpgsql' HANDLER plpgsql_call_handler LANCOMPILER 'PL/pgSQL'; Finally, load the function and object definitions into your database with psql (you must run this as a database user with system privledges): psql -f postgis.sql -d yourdatabase Installation should be complete. UPGRADING: Upgrading PostGIS can be tricky, because the underlying C libraries which support the object types and geometries may have changed between versions. To avoid problems when upgrading, you will have to dump all the tables in your database, destroy the database, create a new one, upload the new postgis.sql file, then upload your database dump: pg_dump -t "*" -f dumpfile.sql yourdatabase dropdb yourdatabase createdb yourdatabase psql -f postgis.sql -d yourdatabase psql -f dumpfile.sql -d yourdatabase vacuumdb -z yourdatabase When upgrading to 0.6, all your geometries will be created with an SRID of -1. To create valid OpenGIS geometries, you will have to create a valid SRID in the SPATIAL_REF_SYS table, and then update your geometries to reference the SRID with the following SQL (with the appropriate substitutions: UPDATE TABLE <table> SET <geocolumn> = SetSRID(<geocolumn>,<SRID>); USAGE: Try the following example SQL statements to create non-OpenGIS tables and geometries: CREATE TABLE geom_test ( gid int4, geom geometry,name varchar(25) ); INSERT INTO geom_test ( gid, geom, name ) VALUES ( 1, 'POLYGON((0 0 0,0 5 0,5 5 0,5 0 0,0 0 0))', '3D Square'); INSERT INTO geom_test ( gid, geom, name ) VALUES ( 2, 'LINESTRING(1 1 1,5 5 5,7 7 5)', '3D Line' ); INSERT INTO geom_test ( gid, geom, name ) VALUES ( 3, 'MULTIPOINT(3 4,8 9)', '2D Aggregate Point' ); SELECT * from geom_test WHERE geom && 'BOX3D(2 2 0,3 3 0)'::box3d; The following SQL creates proper OpenGIS entries in the SPATIAL_REF_SYS and GEOMETRY_COLUMNS tables, and ensures that all geometries are created with an SRID. INSERT INTO SPATIAL_REF_SYS ( SRID, AUTH_NAME, AUTH_SRID, SRTEXT ) VALUES ( 1, 'EPSG', 4269, 'GEOGCS["NAD83", DATUM[ "North_American_Datum_1983", SPHEROID[ "GRS 1980", 6378137, 298.257222101 ] ], PRIMEM["Greenwich",0], UNIT["degree",0.0174532925199433]]' ); CREATE TABLE geotest ( id INT4, name VARCHAR(32) ); SELECT AddGeometryColumn('db','geotest','geopoint',1,'POINT',2); INSERT INTO geotest (id, name, geopoint) VALUES (1, 'Olympia', GeometryFromText('POINT(-122.90,46.97)',1)); INSERT INTO geotest (id, name, geopoint) VALUES (2, 'Renton', GeometryFromText('POINT(-122.22,47.50)',1)); SELECT name,AsText(geopoint) FROM geotest; RTREE vs GIST: PostgreSQL provides support for GiST indexing. The GiST scheme offers indexing even on large objects, using a system of "lossy" indexing where a large object is proxied by a smaller one in the index. In the case of the PostGIS indexing system, all objects are proxied in the index by their bounding boxes. You can build a GiST index with: CREATE INDEX <indexname> ON <tablename> USING gist ( <geometryfield> gist_geometry_ops ) WITH ( islossy ); Note that PostgreSQL may not use the GiST indexes when performing searches unless *forced* to do so. If you find your system is not using the indexes automatically (use 'EXPLAIN' to see the query plan) you can force index use with the command: SET ENABLE_SEQSCAN = OFF Try doing an EXPLAIN on your query before and after the 'enable_seqscan' command to see the different query plans.