Hi Simon,
This is because you are using PointN(geom, int) to iterate over your
MultiPoint geometry. PointN is for selecting the Nth point in a
LineString. Try using GeometryN instead.
postgis=# select geometryn(g.geom::geometry,
postgis(# generate_series(1,npoints(g.geom::geometry)))
postgis-# from (
postgis(# select
postgis(# 'MULTIPOINT(
postgis'# 326454.7 5455793.7,
postgis'# 326621.3 5455813.7,
postgis'# 326827.7 5455841.2,
postgis'# 326771.6 5455831.6)'::geometry as geom
postgis(# ) as g;
geometryn
--------------------------------------------
0101000000CDCCCCCCDAEC1341CDCCCC6CECCF5441
01010000003333333375EF1341CDCCCC6CF1CF5441
0101000000CDCCCCCCAEF21341CDCCCC4CF8CF5441
010100000066666666CEF11341666666E6F5CF5441
(4 rows)
Cheers,
Kevin
Simon Greener wrote:
PostGIS users,
I am having difficulties iterativing over multipoint geometries using a method
similar to this one posted by Kevin Neufeld:
If your linestrings aren't too large (ie < 1000pts), you can actually do
this with a simple query. The reason I say this is because
generate_series doesn't scale well.
postgis=# CREATE TEMP TABLE mylines AS
postgis-# SELECT 'LINESTRING(0 0, 0 1, 1 1, 1 0, 0 0)'::geometry AS geom;
SELECT
postgis=# SELECT AsText( MakeLine(sp,ep) )
postgis-# FROM (
postgis(# SELECT pointn(geom, generate_series(1, npoints(geom)-1)) as sp,
postgis(# pointn(geom, generate_series(2, npoints(geom) )) as ep
postgis(# FROM mylines ) AS foo;
astext
---------------------
LINESTRING(0 0,0 1)
LINESTRING(0 1,1 1)
LINESTRING(1 1,1 0)
LINESTRING(1 0,0 0)
(4 rows)
When I enter the following into PgAdmin:
select pointn(g.geom::geometry,generate_series(1,npoints(g.geom::geometry)))
from (select
'MULTIPOINT(
326454.7 5455793.7,
326621.3 5455813.7,
326827.7 5455841.2,
326771.6 5455831.6)'::geometry as geom) as g;
I get all records reported as being NULL. Checking with:
select case when p.point is null then 'NULL' else 'VALUE' end
from (select
pointn(g.geom::geometry,generate_series(1,npoints(g.geom::geometry))) as point
from (select
'MULTIPOINT(
326454.7 5455793.7,
326621.3 5455813.7,
326827.7 5455841.2,
326771.6 5455831.6)'::geometry as geom) as g ) as p;
All values are reported as NULL.
Any advice? I am running PostgreSQL 8.2.5 and PostGIS 1.3.1 GEOS
3.0.0rc4-CAPI-1.3.3 PROJ 4.5.0
regards
Simon
On Fri, 07 Mar 2008 07:02:01 +1100, <[EMAIL PROTECTED]> wrote:
_______________________________________________
postgis-users mailing list
postgis-users@postgis.refractions.net
http://postgis.refractions.net/mailman/listinfo/postgis-users
