Question

i have a postgres database with millions of rows in it it has a column called geom which contains the boundary of a property.

using a python script i am extracting the information from this table and re-inserting it into a new table.

when i insert in the new table the script bugs out with the following:

Traceback (most recent call last):
  File "build_parcels.py", line 258, in <module>
    main()
  File "build_parcels.py", line 166, in main
    update_cursor.executemany("insert into parcels (par_id, street_add, title_no, proprietors, au_name, ua_name, geom) VALUES (%s, %s, %s, %s, %s, %s, %s)", inserts)
psycopg2.IntegrityError: new row for relation "parcels" violates check constraint "enforce_geotype_geom"

The new table has a check constraint enforce_geotype_geom = ((geometrytype(geom) = ‘POLYGON’::text) OR (geom IS NULL)) whereas the old table does not, so im guessing theres dud data or non polygon (perhaps multipolygon data?) in the old table. i want to keep the new data as polygon so want to not insert anything else.

Initially i tried wrapping the query with standard python error handling with the hope that the dud geom rows would fail but the script would keep running , but the script has been written to commit at the end not each row so it doesnt work.

I think what i need to do is iterate through the old table geom rows and check what type of geometry they are so i can establish whether or not i want to keep it or throw it away before i insert into the new table

Whats the best way of going about this?

Answer 1

This astonishingly useful bit of PostGIS SQL should help you figure it out… there are many geometry type tests in here:

-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-- 
-- $Id: cleanGeometry.sql 2008-04-24 10:30Z Dr. Horst Duester $
--
-- cleanGeometry - remove self- and ring-selfintersections from 
--                 input Polygon geometries 
-- http://www.sogis.ch
-- Copyright 2008 SO!GIS Koordination, Kanton Solothurn, Switzerland
-- Version 1.0
-- contact: horst dot duester at bd dot so dot ch
--
-- This is free software; you can redistribute and/or modify it under
-- the terms of the GNU General Public Licence. See the COPYING file.
-- This software is without any warrenty and you use it at your own risk
--  
-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -


CREATE OR REPLACE FUNCTION cleanGeometry(geometry)
  RETURNS geometry AS
$BODY$DECLARE
  inGeom ALIAS for $1;
  outGeom geometry;
  tmpLinestring geometry;

Begin

  outGeom := NULL;

-- Clean Process for Polygon 
  IF (GeometryType(inGeom) = 'POLYGON' OR GeometryType(inGeom) = 'MULTIPOLYGON') THEN

-- Only process if geometry is not valid, 
-- otherwise put out without change
    if not isValid(inGeom) THEN

-- create nodes at all self-intersecting lines by union the polygon boundaries
-- with the startingpoint of the boundary.  
      tmpLinestring := st_union(st_multi(st_boundary(inGeom)),st_pointn(boundary(inGeom),1));
      outGeom = buildarea(tmpLinestring);      
      IF (GeometryType(inGeom) = 'MULTIPOLYGON') THEN      
        RETURN st_multi(outGeom);
      ELSE
        RETURN outGeom;
      END IF;
    else    
      RETURN inGeom;
    END IF;


------------------------------------------------------------------------------
-- Clean Process for LINESTRINGS, self-intersecting parts of linestrings 
-- will be divided into multiparts of the mentioned linestring 
------------------------------------------------------------------------------
  ELSIF (GeometryType(inGeom) = 'LINESTRING') THEN

-- create nodes at all self-intersecting lines by union the linestrings
-- with the startingpoint of the linestring.  
    outGeom := st_union(st_multi(inGeom),st_pointn(inGeom,1));
    RETURN outGeom;
  ELSIF (GeometryType(inGeom) = 'MULTILINESTRING') THEN 
    outGeom := multi(st_union(st_multi(inGeom),st_pointn(inGeom,1)));
    RETURN outGeom;
  ELSIF (GeometryType(inGeom) = '<NULL>' OR GeometryType(inGeom) = 'GEOMETRYCOLLECTION') THEN 
    RETURN NULL;
  ELSE 
    RAISE NOTICE 'The input type % is not supported %',GeometryType(inGeom),st_summary(inGeom);
    RETURN inGeom;
  END IF;     
End;$BODY$
  LANGUAGE 'plpgsql' VOLATILE;