I think you're right ... there isn't a simple answer to your problem.
A complicated approach might be something like:
1. extract the boundary lines from your polygons.
2. convert the boundary lines into a collection of two-coordinate linestrings.
3. remove the closest pairs of linestrings from neighbouring polygons.
4. collect the lines and repolygonize.
-- Kevin
Travis Kirstine wrote:
I don't think that the geom union would in combination with the
boundary would attach the island to the mainland. I don't think that
there is a simple answer to my problem but I have attached a pic to
help illustrate what I'm trying to accomplish.
Regards
2008/11/21 Lee Meilleur <[EMAIL PROTECTED]>:
Howabout ST_BOUNDARY(ST_UNION(the_geom))
________________________________________
From: [EMAIL PROTECTED] [EMAIL PROTECTED] On Behalf Of Burgholzer,Robert [EMAIL
PROTECTED]
Sent: Friday, November 21, 2008 12:45 PM
To: PostGIS Users Discussion
Subject: RE: [postgis-users] return boundary
So,
Do you need to iterate through the sub-polygons in your multi and get a
boundary of each?
r.b.
Robert W. Burgholzer
Surface Water Modeler
Office of Water Supply and Planning
Virginia Department of Environmental Quality
[EMAIL PROTECTED]
804-698-4405
Open Source Modeling Tools:
http://sourceforge.net/projects/npsource/
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of
Travis Kirstine
Sent: Friday, November 21, 2008 10:51 AM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] return boundary
Thanks Obe
But I'm looking for something that returns the boundary of all the
selected features combined and attached. Something that has the
abilty to take the group the features together like convex hull but
keep the detail of the of the edge like boundary.
2008/11/21 Obe, Regina <[EMAIL PROTECTED]>:
How about ST_Boundary?
http://postgis.refractions.net/documentation/manual-svn/ST_Boundary.html
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of
Travis Kirstine
Sent: Friday, November 21, 2008 10:18 AM
To: PostGIS Users Discussion
Subject: [postgis-users] return boundary
I have a multipolygon that has consists mainland and island polygons.
I need to generate a single polygon / line that represent the boundary
of the multipolygon as a whole, something like a convex hull but
keeping the detail of the outer rings and joining the islands to the
mainland. I have been try different combos of convex hull, buffer and
difference but can't get what I'm looking for.
Any thoughts would be greatly appreciated
Regards
--
Travis K.
Toronto, Canada
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--
Travis K.
Toronto, Canada
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"She knows there's no success like failure
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-Bob Dylan-
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