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
<http://newtb.info/>, multi(buffer(geomunion(distinct
newtb.cgeom), 0.0)) as thenewgeom
FROM
( SELECT a.code, b.info
<http://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 <http://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 <http://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 <http://newtb.info/>,
geomunion(newtb.cgeom) as thenewgeom
FROM
( SELECT a.code, b.info <http://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 <http://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 <http://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
<http://www.kodakgallery.com/I.jsp?c=cjns10h3.8ovw4dsn&x=0&y=w3kbw0>
Ravi Kumar
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