[postgis-users] New function ST_DumpSegments?? (was : utility function : linestring -> setof segment)

[Rémi Cura]

Yep,
would need some wrapping to output right path :-)

I'd really like to have more functions in PostGis...

I'm not going to do it yet, working on a SnapToLine function.

Cheers,
Rémi-C


2013/10/30 Nicolas Ribot <nicolas.ribot at gmail.com>

> Hi,
>
> To dump (multi)polygons boundaries, you can use:
> st_exteriorRing((st_dumpRings((st_dump(geom)).geom)).geom)
>
> I returns one linestring for each boundary, taking holes into account.
>
> Nicolas
>
> On 30 October 2013 14:34, Rémi Cura <remi.cura at gmail.com> wrote:
> > Hey,
> > here is the function, safe for geometry collection and multilinestring as
> > well.
> > It mimics ST_DumpPoints.
> >
> > It doesn't work on polygon as we would first need a method STDumpLines.
> >
> >
> > Origine of segments is preserved inside the path when multi.
> > Could it be added to core ?
> > Shall I add a ticket?
> >
> > Cheers,
> > Rémi-C
> >
> > /////////////////////////////////
> >
> > DROP FUNCTION IF EXISTS public.DumpSegments(line geometry ) ;
> > CREATE OR REPLACE FUNCTION public.DumpSegments(_line geometry)
> > RETURNS SETOF geometry_dump
> > AS
> > $BODY$
> > --this function breaks a line into minimal segments and return it
> > DECLARE
> > _r record;
> > BEGIN
> >
> > FOR _r in SELECT ST_Dump(ST_CollectionExtract (_line,2)) AS dp
> > LOOP
> > RETURN QUERY WITH line AS(
> > SELECT --ST_GeomFromText('LINESTRING(12 1, 13 1, 14 2, 15 4)') AS line
> > (_r.dp).path AS gpath, (_r.dp).geom AS line
> > ),
> > dump AS(
> > SELECT gpath[1] AS gpath, (ST_DumpPoints(line)) as dp
> > FROM line
> > ),
> > segments AS (
> > SELECT CASE WHEN gpath IS NULL THEN ARRAY[(dp).path[1]-1] ELSE
> ARRAY[gpath,
> > (dp).path[1]-1] END AS path,ST_MakeLine( lag((dp).geom , 1, NULL) OVER
> > (ORDER BY  (dp).path),(dp).geom) AS geom
> > FROM dump
> > )
> > SELECT path,geom
> > FROM segments
> > WHEre geom  IS NOT NULL;
> > END LOOP;--loop if multi linestring
> > RETURN;
> > END;
> > $BODY$
> >  LANGUAGE plpgsql  IMMUTABLE STRICT;
> >
> >
> > SELECT public.DumpSegments(line2)
> > FROM ST_GeomFromText('MULTILINESTRING((12 1, 13 1, 14 2, 15 4),(1 1, 2
> 2,3
> > 3))') AS line1,ST_GeomFromText( 'LINESTRING(12 1, 13 1, 14 2, 15 4)') AS
> > line2
> >
> >
> >
> >
> > //////////////////////////////////////
> >
> >
> >
> >
> > 2013/10/30 Rémi Cura <remi.cura at gmail.com>
> >>
> >> Thanks,
> >> wanted to do it the clean way (geos accelerated maybe?),
> >>
> >> but not so much a big deal, I'll go you way.
> >>
> >> Cheers,
> >> Rémi-C
> >>
> >>
> >> 2013/10/30 Nicolas Ribot <nicolas.ribot at gmail.com>
> >>>
> >>> Hi,
> >>>
> >>> I don't think such a function exists in postgis.
> >>> (To achieve that, I usually dump line points and create new
> >>> linestrings with vertices n, n+1)
> >>>
> >>> Nicolas
> >>>
> >>> On 30 October 2013 10:59, Rémi Cura <remi.cura at gmail.com> wrote:
> >>> > Hey,
> >>> > is somebodyers aware of a function breaking a linestring into a set
> of
> >>> > segments (mathematical meaning),
> >>> > without introducing new points?
> >>> >
> >>> > Cheers,
> >>> >
> >>> >
> >>> > Rémi-C
> >>> >
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> >>
> >>
> >
> >
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