Dylan, Are you trying to make them all the same or all into POLYGONS? If you end up with POLYGONS that don't touch (which is quite common with st_intersection even n non-sliver cases) I think they have to be represented as MULTIPOLYGONS so the best you can do is row creation and break each out into a separate record or make your POLYGON a multi by doing
ST_Multi(ST_Intersection(...)) so you can put constraints on it. Hope that helps, Regina -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Dylan Beaudette Sent: Tuesday, April 22, 2008 6:04 PM To: PostGIS Mailingliste Subject: [postgis-users] st_intersection() outputs multipolygons Hi, I have two imput tables with all polygon geometry types, all polygons are reported as valid. After performing an intersection, I am left with mixed polygon and multipolygon geometry types: CREATE TABLE dwr.mapunit_dau as SELECT m_polys.areasymbol, m_polys.mukey, d_polys.dau_id, ST_Intersection(d_polys.wkb_geometry, m_polys.wkb_geometry) as wkb_geometry FROM ( -- subset map unit polygons to certain survey areas -- 6.540 s SELECT wkb_geometry, areasymbol, mukey FROM mapunit_poly -- results in 21682 map unit polygons WHERE areasymbol in ('ca653', 'ca654', 'ca113') ) as m_polys JOIN ( -- subset DAU polygons that overlap with specific survey areas -- 512 ms SELECT dwr.dau.wkb_geometry, dau.dau3_d_id as dau_id FROM dwr.dau JOIN mapunit_bound_poly -- results in 58 DAU polygons ON mapunit_bound_poly.areasymbol in ('ca653', 'ca654', 'ca113') and dwr.dau.wkb_geometry && mapunit_bound_poly.wkb_geometry ) as d_polys -- join condition: only those polygons which completely intersect ON ST_Intersects(d_polys.wkb_geometry, m_polys.wkb_geometry); -- -- -- Looking at the results, I have several geometry types with several total geometries per original feature: SELECT DISTINCT GeometryType(wkb_geometry), ST_NumGeometries(wkb_geometry) from mapunit_dau; geometrytype | st_numgeometries --------------+------------------ MULTIPOLYGON | 2 MULTIPOLYGON | 3 MULTIPOLYGON | 4 MULTIPOLYGON | 5 MULTIPOLYGON | 6 MULTIPOLYGON | 7 MULTIPOLYGON | 8 MULTIPOLYGON | 9 MULTIPOLYGON | 10 MULTIPOLYGON | 11 MULTIPOLYGON | 12 MULTIPOLYGON | 13 MULTIPOLYGON | 14 MULTIPOLYGON | 15 MULTIPOLYGON | 16 MULTIPOLYGON | 18 MULTIPOLYGON | 21 MULTIPOLYGON | 24 MULTIPOLYGON | 26 MULTIPOLYGON | 27 MULTIPOLYGON | 32 MULTIPOLYGON | 36 MULTIPOLYGON | 41 MULTIPOLYGON | 52 MULTIPOLYGON | 56 MULTIPOLYGON | 69 POLYGON | I have checked, and these multipolygons represent large features, not sliver-like artifacts that are commonly left-over from an intersection. Also, they contain useful information (non-overlapping polygons) as I traverse the geometry tree with GeometryN()... Any ideas? Cheers, Dylan -- Dylan Beaudette Soil Resource Laboratory http://casoilresource.lawr.ucdavis.edu/ University of California at Davis 530.754.7341 _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users ----------------------------------------- The substance of this message, including any attachments, may be confidential, legally privileged and/or exempt from disclosure pursuant to Massachusetts law. It is intended solely for the addressee. If you received this in error, please contact the sender and delete the material from any computer. _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
