Hi,
a and b, are multiple tables derived from -2- shape files saved as POST-GIS
data.
Slide 1:
'a' this data as in the slide show has attributes, This is a square with
polygons.
'b' as in the slide show is made up of 2 polygons with attributes which overlap
'a'.
Slide 2: a and b are in UNION with the syntax below. But this is not the
desired result. There are polygons overlapping other polygons, one below the
other.
Slide 3:
'abc' is a union of a and b, with desired result
My further analysis with post GIS awaits HELP.
Cheers
Ravi Kumar
"Obe, Regina" <[EMAIL PROTECTED]> wrote: Ravi,
Is the graphic one record or multiple records? If multiple records - I'm
afraid you may be asking 2 conflicting questions depending on your dataset so
I'm not sure there is anything that can remedy that aside from treating them
as two separate questions.
I'm also afraid you are getting into territory I'm very weak. You may want
to investigate use of st_boundary (which will give you a multilinestring of
a polygon/multipolygon boundary and then apply buildarea to that).
The below should get rid of some redundant overlapping polygons, but probably
won't completely satisfy what you want to do. I'm also thinking you may want
to be using intersection instead of geomunion for the inner part. But again
depends what you are trying to answer.
INSERT INTO abc(code, info, the_geom)
SELECT newtb.code, newtb.info, multi(buffer(geomunion(distinct newtb.cgeom),
0.0)) as thenewgeom
FROM
( SELECT a.code, b.info, intersection(a.geometry, b.geometry) as cgeom
FROM a
INNER JOIN b ON a.geometry && b.geometry AND intersects(a.geometry,
b.geometry)
UNION ALL
SELECT a.code, null As info, a.geometry as cgeom FROM a
LEFT JOIN b ON a.geometry && b.geometry AND intersects(a.geometry,
b.geometry)
WHERE b.geometry IS NULL
UNION ALL
SELECT null as code, b.info, b.geometry as cgeom
FROM b LEFT JOIN a ON a.geometry && b.geometry AND
intersects(a.geometry, b.geometry)
WHERE a.geometry IS NULL
) AS newtb
GROUP BY newtb.code, newtb.info
Hope that helps,
Regina
---------------------------------
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of RAVI KUMAR
Sent: Monday, September 17, 2007 9:04 AM
To: postgis
Subject: [postgis-users] UNION
Hi Regina,
giving the link to show actual how the UNION of polygons is not working as
per expectation.
Please see the clips in the link.
CREATE TABLE abc(code smallint, info smallint) with oids;
SELECT AddGeometryColumn('public', 'abc', 'the_geom', 4326, 'MULTIPOLYGON',
2);
--The insert
INSERT INTO abc(code, info, the_geom)
SELECT newtb.code, newtb.info, geomunion(newtb.cgeom) as thenewgeom
FROM
( SELECT a.code, b.info, geomunion(a.geometry, b.geometry) as cgeom
FROM a
INNER JOIN b ON a.geometry && b.geometry AND intersects(a.geometry,
b.geometry)
UNION ALL
SELECT a.code, null As info, a.geometry as cgeom FROM a
LEFT JOIN b ON a.geometry && b.geometry AND intersects(a.geometry,
b.geometry)
WHERE b.geometry IS NULL
UNION ALL
SELECT null as code, b.info, b.geometry as cgeom
FROM b LEFT JOIN a ON a.geometry && b.geometry AND
intersects(a.geometry, b.geometry)
WHERE a.geometry IS NULL
) AS newtb
GROUP BY newtb.code, newtb.info
May be I should be using different syntax for such a result.
http://www.kodakgallery.com/I.jsp?c=cjns10h3.8ovw4dsn&x=0&y=w3kbw0
Ravi Kumar
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