Hi Craig,
What is it you are trying to do exactly?
Reading your query, I see that you are interested in the intersection of
all geometries in "evc" and "bnd_buf" where the geometries overlap (by
definition, this means that the interior of one polygon is both inside
and outside that of another polygon) and where "buf_dist" = 1. So,
you're not interested in cases where a polygon in "env" is contained
wholly inside "bnd_buf". Right?
Did you mean to filter with "overlaps"? Or did you mean "intersects"?
-------------
Kevin Neufeld
Software Developer
Refractions Research Inc.
300-1207 Douglas St.
Victoria, B.C., V8W 2E7
Phone: (250) 383-3022
Email: [EMAIL PROTECTED]
Craig Feuerherdt wrote:
I have been attempting to intersect on set of geometries (bio.evc)
with another geometry (bio.bnd_buf). All the geometries are valid
according to isvalid and the query below successfully returns a table.
create table bio.bnd_evc as
select a.buf_dist, b.bio_no, b.bio_code, b.evc, b.constcde,
b.consstat, b.density, intersection(a.the_geom, b.the_geom) as the_geom
from bio.bnd_buf as a, bio.evc as b
where a.the_geom && b.the_geom
and a.buf_dist = 1
and overlaps(a.the_geom, b.the_geom)
When I view the resulting table (bnd_evc) in QGIS there are several
missing polygons ( image 1a
<http://www.bendigo-orienteers.com.au/study/evc1_over.png>). One of
the polygons lies entirely within bnd_bnf while the other has a small
portion which overlaps the boundary.
When I try intersecting the same geometries but this time selecting
buf_dist = 1000 (the 1000m buffer), additional evc polygons (which are
wholly within buf_dist=1 and therefore also within buf_dist=1000) are
missing from the output table and the whole thing is a 'mess' nad is
in no way a representation of what the intersection shoul dlook like (
image 2a <http://www.bendigo-orienteers.com.au/study/evc1000_over.png>).
The other thing that occurs in both cases is that some polygon
geometries are created where there are no evc polygons ( image 1b
<http://www.bendigo-orienteers.com.au/study/evc1_under.png> & 2b
<http://www.bendigo-orienteers.com.au/study/evc1000_under.png>).
Both tables have a GIST index on the geometry column (the_geom).
Are the issues associated with having multiple polygon geometries in
the one table (unlikely in my opinion)?
Is it something to do with the query?
Are these issues associated with PostGIS or GEOS?
Is there a work around to solve the issue?
Thanks in advance,
Craig
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