[postgis-users] how to create ouline of multiple objects

[Ben Madin]

 From what you've described maybe ST_ConvexHull() is what you are after?

cheers

Ben


On 14/08/2009, at 3:11 AM, G. van Es wrote:

> Leo/Paul,
>
> Indeed, a bunch of polygons (900) of wich I need the outline. In  
> fact drawing one line around the objects.
>
> I tried st_union but this returns an empty result.
> st_exteriorRing returns lines from polygons but still the same  
> number of objects.
>
> Might be close to it but I'm still struggling with it.
>
> Ge
>
>
> --- On Thu, 8/13/09, Paragon Corporation <lr at pcorp.us> wrote:
>
>> From: Paragon Corporation <lr at pcorp.us>
>> Subject: Re: [postgis-users] how to create ouline of multiple objects
>> To: "'PostGIS Users Discussion'" <postgis-users at postgis.refractions.net 
>> >
>> Date: Thursday, August 13, 2009, 11:54 AM
>> Ge,
>>
>> What do you mean by outline of all objects?  You
>> mean  if you have a bunch
>> of polygons you just want one record with all boundaries
>> dissolved?
>>
>> Maybe you are looking for ST_Union
>>
>> SELECT ST_Union(the_geom)
>> FROM sometable
>>
>> That will dissolve boundaries.
>> http://postgis.refractions.net/documentation/manual-svn/ST_Union.html
>>
>> or you mean you have a polygon and you want the linestring
>> outline.
>>
>> For that use ST_Boundary(the_geom) or ST_ExteriorRing
>> http://postgis.refractions.net/documentation/manual-svn/ST_Boundary.html
>>
>> http://postgis.refractions.net/documentation/manual-svn/ST_ExteriorRing.html
>>
>>
>>
>> Leo
>>
>> -----Original Message-----
>> From: postgis-users-bounces at postgis.refractions.net
>> [mailto:postgis-users-bounces at postgis.refractions.net]
>> On Behalf Of G. van
>> Es
>> Sent: Thursday, August 13, 2009 2:48 PM
>> To: PostGIS Users Discussion
>> Subject: [postgis-users] how to create ouline of multiple
>> objects
>>
>> Hi All,
>>
>> Maybe a stupid question but I have a shape imported in PG
>> of wich I want to
>> determine the outline of all objects. The result should be
>> a LINE or just
>> one POLYGON.
>>
>> Does anyone know if this is possible in PG.
>>
>> Thanks,
>>
>> Ge
>>
>>
>>
>> _______________________________________________
>> postgis-users mailing list
>> postgis-users at postgis.refractions.net
>> http://postgis.refractions.net/mailman/listinfo/postgis-users
>>
>>
>>
>> _______________________________________________
>> postgis-users mailing list
>> postgis-users at postgis.refractions.net
>> http://postgis.refractions.net/mailman/listinfo/postgis-users
>>
>
>
>
> _______________________________________________
> postgis-users mailing list
> postgis-users at postgis.refractions.net
> http://postgis.refractions.net/mailman/listinfo/postgis-users

-- 

Ben Madin
REMOTE INFORMATION

t : +61 8 9192 5455
f : +61 8 9192 5535
m : 0448 887 220
Broome   WA   6725

ben at remoteinformation.com.au



							Out here, it pays to know...