CREATE TEMP TABLE mypolygontable AS
SELECT
'MULTIPOLYGON(((0 0, 0 4, 4 4, 4 0, 0 0),
(1 1, 1 2, 2 2, 2 1, 1 1)),
((5 5, 5 6, 6 6, 6 5, 5 5))
)'::geometry geom;
-- make line segments from every startpoint and endpoint
SELECT ST_AsText( ST_MakeLine(sp,ep) )
FROM
-- extract the endpoints for every 2-point line segment for each linestring
(SELECT
ST_PointN(geom, generate_series(1, ST_NPoints(geom)-1)) as sp,
ST_PointN(geom, generate_series(2, ST_NPoints(geom) )) as ep
FROM
-- extract the individual linestrings
(SELECT (ST_Dump(ST_Boundary(geom))).geom
FROM mypolygontable
) AS linestrings
) AS segments;
st_astext
---------------------
LINESTRING(0 0,0 4)
LINESTRING(0 4,4 4)
LINESTRING(4 4,4 0)
LINESTRING(4 0,0 0)
LINESTRING(1 1,1 2)
LINESTRING(1 2,2 2)
LINESTRING(2 2,2 1)
LINESTRING(2 1,1 1)
LINESTRING(5 5,5 6)
LINESTRING(5 6,6 6)
LINESTRING(6 6,6 5)
LINESTRING(6 5,5 5)
(12 rows)
Cheers,
Kevin
On 1/29/2010 5:16 AM, Nicolas Gillet - MARKET-IP wrote:
Hello,
I am looking for some tips to split a polygon to its simplest linestrings.
An example worth better than words :
POLYGON((0 0, 0 1, 1 1, 1 0, 0 0))
Would become :
MULTINLINESTRING((0 0, 0 1), (0 1, 1 1), (1 1, 1 0), (1 0, 0 0))
Every single linestring has to have two and only two points.
Is there a way to do this with the existing postgis functions ?
I found several ways to turn a polygon to a (multi)linestring but not to
split it then into shortest linestrings.
Thanks for any input.
Nicolas
Gillet
_______________________________________________
postgis-users mailing list
[email protected]
http://postgis.refractions.net/mailman/listinfo/postgis-users
_______________________________________________
postgis-users mailing list
[email protected]
http://postgis.refractions.net/mailman/listinfo/postgis-users
