Le 29/12/2009 11:39, Nicolas Gillet - MARKET-IP a écrit :
I am trying to aggregate linestrings together based on their attributes and
the fact that they are touching each other.
Therefore I found out how to write a very basic aggregate function :
CREATE AGGREGATE geometry_sum (
SFUNC = st_union,
BASETYPE = geometry,
STYPE = geometry);
Nicolas, what does your geometry_sum function do precisely ?
There is a ST_Linemerge function that takes a collection of linestrings
as an argument and merges them together into a multilinestring.
Maybe it doesn't give you the result you expect ?
With a table "thetable" having an "attrib" field and a "geom" field, I
would write the query like this :
SELECT attrib, (st_dump(merged_geom)).geom
FROM (
SELECT attrib, ST_Linemerge(ST_Collect(geom)) AS merged_geom
FROM thetable
GROUP BY attrib
) AS subq;
Does this solve your problem ?
Regards,
Arnaud
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