Gustavo,
It sounds like the dump command may work for you.
However it seems to me that you still may be trying to tackle a
slightly different issue:
how to convert your multilinestrings into single linestrings (each on
a row) and merge them in such a way to be collected along with all
other contiguous linestrings that share end/start points.
A moment ago in IRC bitner kindly helped me work out these steps that
may be helpful for you:
--Create testing multipolygon data with two linestrings that share
endpoints and another that is free floating
drop table if exists lines;
create table lines (id serial,the_geom geometry);
INSERT into lines (the_geom) values (geomfromtext('MULTILINESTRING
((4.8938679245283 46.3443396226415,33.313679245283
73.7028301886792,49.5872641509434 80.0707547169811),(49.5872641509434
80.0707547169811,90.9583136792453 89.2813679245283,54.3363797169811
103.03608490566,29.0620872641509 103.293985849057,12.2125589622641
107.1625,11.1624233831055 106.590266209164,10.4214805264064
107.529010012923,11.2220067193803 108.417488521584,12.2326314413493
107.778056025276),(37.506947728971 97.6302534161404,12.1756482134062
82.9892270906306))',-1));
--Disaggregate multilines into linestrings, one per row
drop table if exists single_lines;
SELECT generate_series(1,(Select ST_NumGeometries(the_geom))) as id,
ST_GeometryN(the_geom, generate_series(1, ST_NumGeometries
(the_geom))) AS the_geom
into single_lines FROM lines;
--Collect and merge all linestrings
drop table if exists bitner_collected;
SELECT st_linemerge(Collect(the_geom)) as the_geom
into bitner_collected from single_lines;
--Disagregate the resulting multilinestring resulting in continguous
linestrings, again one per row
drop table if exists single_lines_again;
SELECT generate_series(1,(Select ST_NumGeometries(the_geom))) as id,
ST_GeometryN(the_geom, generate_series(1, ST_NumGeometries
(the_geom))) AS the_geom
into single_lines_again FROM bitner_collected;
Cheers,
Dane
ps. please anyone let me know if the text formatting is helpful or
just annoying.
On Feb 6, 2008, at 9:30 AM, Kevin Neufeld wrote:
Hi Gus,
Glad to help!
Actually, it is documented, (http://postgis.refractions.net/docs/
ch06.html#id2704158) though I agree it definitely could be clearer,
i.e. with some examples.
Here are some more links/examples to PostgreSQL's set returning
functions...
http://www.postgresql.org/docs/8.2/static/xfunc-sql.html
http://www.postgresql.org/docs/8.2/static/functions-srf.html
Hope this helps,
-- Kevin
Gustavo Ces wrote:
thanks Kevin!
Now i understand which was the problem!
And you run faster, how to extract geometry from geometry_dump
type (?) was the next question! :)
It´s not documentated, so i supose it´s a composite type and
you know how to access it after search that type in database, don
´t you?
Gus
----- Original Message ----- From: "Kevin Neufeld"
<[EMAIL PROTECTED]>
To: "PostGIS Users Discussion" <postgis-
[EMAIL PROTECTED]>
Sent: Wednesday, February 06, 2008 5:22 PM
Subject: Re: [postgis-users] multiline to linestring
Hi Gus,
As noted from your error, ST_Dump() is a set returning function,
ie. you need to perform something like 'select * from dump(...)'
Try this:
select geom from dump(
(select linemerge(collect(the_geom)) from lines)
);
Cheers,
-- Kevin
Gustavo Ces wrote:
Hi all,
i´ve got a problem with ST_Dump() ( well, actually this one
doesn´t exist )
and dump() function. I´m working with
"PostgreSQL 8.2.3 on i686-pc-mingw32, compiled by GCC gcc.exe
(GCC) 3.4.2 (mingw-special)"
"POSTGIS="1.2.1" GEOS="2.2.3-CAPI-1.1.1" PROJ="Rel. 4.5.0, 22
Oct 2006" USE_STATS"
I want to convert linestrings from multilinestrings, with
linemerge, to obtain united linestrings in overlapping points
with this sentence:
select dump(linemerge(collect(the_geom))) from lines
but i obtain:
ERROR: set-valued function called in context that cannot accept
a set
Estado SQL:0A000
The result of:
select astext(LineMerge(Collect(the_geom))) from lines
is:
"MULTILINESTRING((4.8938679245283
46.3443396226415,33.313679245283
73.7028301886792,49.5872641509434
80.0707547169811,90.9583136792453
89.2813679245283,54.3363797169811
103.03608490566,29.0620872641509
103.293985849057,12.2125589622641 107.1625,11.1624233831055
106.590266209164,10.4214805264064
107.529010012923,11.2220067193803
108.417488521584,12.2326314413493 107.778056025276),
(37.506947728971 97.6302534161404,12.1756482134062
82.9892270906306))"
with numgeometries=2, the logic result with my original data.
How can i extract those linestrings separately?
Gus
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