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
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