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Re: St_boundary and illegal argument exception

by Paragon Corporation-2 :: Rate this Message:

George,

Use generate series in combination with ST_PointN. So just change the FROM of this with your table and also increase the 1000 to the maximum number of points you have in any line in your polygon. This will only work with LINESTRING. If you need to work with MULTILINESTRING you'll need to include ST_Dump in there.

SELECT gid, ST_MakeLine(ST_PointN(the_geom, n),ST_PointN(the_geom,n+1)) As geomwkt

FROM (VALUES (1 , ST_GeomFromText('LINESTRING(1 2, 3 4, 5 8, 6 10)') ) ,

(2 , ST_GeomFromText('LINESTRING(1 2, -1 -2)') ))

As foo(gid,the_geom)

CROSS JOIN generate_series(1, 1000) As n

WHERE n < ST_Npoints(foo.the_geom);

Leo

From: postgis-users-bounces@... [mailto:postgis-users-bounces@...] On Behalf Of George Silva
Sent: Friday, June 26, 2009 10:42 PM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] St_boundary and illegal argument exception

I ran a st_isvalid on all features of my table. I had 4 invalid features. deleted em, everything worked.

But how about transforming that linestring, into lines?

Example, i have a square, and i need to have all four lines that compose it into separate records.

Is that possible?

George

On Fri, Jun 26, 2009 at 11:41 PM, Kevin Neufeld <kneufeld@...> wrote:

I'm not sure exactly what you are trying to do, but yes, ST_Boundary does extract linework (aka. the boundary) from a polygon.

SELECT ST_AsText(ST_Boundary('POLYGON((0 0, 1 1, 1 0, 0 0))'::geometry));
st_astext -----------------------------
LINESTRING(0 0,1 1,1 0,0 0)
(1 row)

Can you isolate the geometry that is causing you grief?
-- Kevin

George Silva wrote:

Hello everyone.

I'm trying to build a function that will transforma one polygon into many lines. I have a lot table, and i would like to insert each line from each lot in a table, containing the id of the lot.

I've tried: SELECT gid, St_boundary(the_geom) INTO lines from lots and postgis gave me an error:

*NOTICE: IllegalArgumentException: Number of points must be 0 or >3
ERROR: POSTGIS2GEOS conversion failed

********** Erro **********

ERROR: POSTGIS2GEOS conversion failed
SQL state: XX000*

I'm wondering if that is the right approach? I'm not even sure if boundary is what i am looking for. Can anyone help me? Why postgis gave me this error?

Thanks in advanced.

George

--
George R. C. Silva
Sigma Consultoria

Desenvolvimento em GIS
www.consultoriasigma.com.br <http://www.consultoriasigma.com.br>
www.sigmaconsultoria.blogspot.com <http://www.sigmaconsultoria.blogspot.com>
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--
George R. C. Silva
Sigma Consultoria

Desenvolvimento em GIS
www.consultoriasigma.com.br
www.sigmaconsultoria.blogspot.com

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