[postgis-users] Create POLYGON from Several LINESTRINGs

[Randall, Eric]

I think perhaps st_buildarea and st_collect might be what you want.  Below is what I used to create a hexagon out of points->lines which was then translated (using generate_series) across X and Y to create a hexagonal grid for the County.   There's probably a simpler way to make a hexagon but it illustrates the st_buildarea.  Maybe that helps.
 
-Eric 
 
 
 
 
--let's make a hexagon with 1000 foot sides and position it with it's 
--center at 1210000, 610000 (the lower left of the pamap tile extent for Erie County)
--and create a table 
 
drop table if exists hex1000;
create table hex1000 as
select translate(st_buildarea(st_collect(geom)),1210000, 610000) as geom  from 
(select makeline(st_endpoint(makeline(makepoint(0, 0),makepoint(0, - 1000))),st_endpoint(rotate(makeline(makepoint(0, 0),makepoint(0, -1000)), radians(300)))) as geom 
union select makeline(st_endpoint(rotate(makeline(makepoint(0, 0),makepoint(0, -1000)), radians(300))),st_endpoint(rotate(makeline(makepoint(0, 0),makepoint(0, -1000)), radians(240))))  as geom 
union select makeline(st_endpoint(rotate(makeline(makepoint(0, 0),makepoint(0, -1000)), radians(240))),st_endpoint(rotate(makeline(makepoint(0, 0),makepoint(0, -1000)), radians(180))))  as geom 
union select makeline(st_endpoint(rotate(makeline(makepoint(0, 0),makepoint(0, -1000)), radians(180))),st_endpoint(rotate(makeline(makepoint(0, 0),makepoint(0, -1000)), radians(120))))  as geom 
union select makeline(st_endpoint(rotate(makeline(makepoint(0, 0),makepoint(0, -1000)), radians(120))),st_endpoint(rotate(makeline(makepoint(0, 0),makepoint(0, -1000)), radians(60))))  as geom 
union select makeline(st_endpoint(rotate(makeline(makepoint(0, 0),makepoint(0, -1000)), radians(60))),st_endpoint(rotate(makeline(makepoint(0, 0),makepoint(0, -1000)), radians(0))))  as geom 
) as t1;
 
 
 
 
 

-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net [mailto:postgis-users-bounces at postgis.refractions.net]On Behalf Of Avery Penniston
Sent: Tuesday, June 22, 2010 2:38 PM
To: postgis-users at postgis.refractions.net
Subject: Re: [postgis-users] Create POLYGON from Several LINESTRINGs



I'm trying to create 'pie wedge' shaped polygons by building them in a Postgres function.  I am able to create the 2 straight chords and the arc as separate LINESTRINGs, and I have verified that each LINESTRING shares its endpoints with the other two LINESTRINGs.  However, I am having trouble putting the individual parts together to form a POLYGON.

 

I tried to ST_UNION the 3 LINESTRINGs together, and the result is a MULTILINESTRING.  I then call ST_LINEMERGE to convert the MULTILINESTRING to a single LINESTRING so I can pass it to the ST_POLYGON function, but the result of the ST_LINEMERGE is a MULTILINESTRING.  

 

I tried using ST_COLLECT instead of ST_UNION, but then I got a GEOMETRYCOLLECTION containing a MULTILINESTRING and a LINESTRING.

 

Does anybody have some advice for creating a POLYGON from 3 or more separate LINESTRINGs?

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