[postgis-users] Divide 1 Polygon into 2 polygons with a linestring

[Martin Davis]

Yep, absolutely.  In fact, that's probably the only situation in which you could reasonably apply the "add a box to the line" technique.

I'm still hopeful I'll be able to provide a generic solution to this problem in JTS - I know how to do it, and have all the hard code written - it's just finding time to turn it into a usable API.

Martin Davis, Senior Technical Architect
Vivid Solutions Inc.      www.vividsolutions.com
Suite #1A-2328 Government Street Victoria, B.C. V8T 5G5
Phone: (250) 385 6040 - Local 308 Fax: (250) 385 6046


> -----Original Message-----
> From: postgis-users-bounces at postgis.refractions.net 
> [mailto:postgis-users-bounces at postgis.refractions.net] On 
> Behalf Of Stephen Woodbridge
> Sent: May 12, 2006 12:20 PM
> To: PostGIS Users Discussion
> Subject: Re: [postgis-users] Divide 1 Polygon into 2 polygons 
> with a linestring
> 
> 
> Martin, Baris,
> 
> It might be slightly simpler to do if you enforce the constraint that 
> the linestring end points are OUTSIDE the bbox of the 
> polygon. In this 
> case you can intersect the linestring with the bbox of the 
> polygon (or 
> slightly expanded bbox) the construct a polygon based on the 
> intersection points, the linestring intersected with the bbox 
> and half 
> the bbox based on the intersection. Once you have this, 
> intersection and 
> difference of the constructed polygon and the original 
> polygon will give 
> you the two pieces you want.
> 
> Yes, this is a little bit of work by it is well defined, and fairly 
> straight forward and could be all done in a plpgsql stored procedure.
> 
> -Steve W
> 
> Martin Davis wrote:
> > Currently there's no code in JTS which will do this, and not really 
> > any
> > sequence of operations which will perform this easily.  The obvious 
> > thing to try is to extend the linestring far enough to be 
> able to "bend 
> > it around" into a polygon, which you can then use to cut the other 
> > polygon (via intersection and difference).  But this is 
> awkward and not 
> > a general solution.
> >  
> > There is a general solution to this, but it requires a more fully
> > developed set of topological classes than are currently in JTS.
> >  
> > This is probably the most-requested enhancement for JTS.  
> Hopefully we
> > will get time & funding sometime soon to implement this.
> >  
> >  
> > *Martin Davis, Senior Technical Architect*
> > *Vivid Solutions Inc.      /www.vividsolutions.com/*
> > /Suite #1A-2328 Government Street Victoria, B.C. V8T 5G5
> > Phone: (250) 385 6040 - Local 308 Fax: (250) 385 6046/
> > 
> >     -----Original Message-----
> >     *From:* postgis-users-bounces at postgis.refractions.net
> >     [mailto:postgis-users-bounces at postgis.refractions.net] 
> *On Behalf Of
> >     *Baris YILMAZ
> >     *Sent:* May 12, 2006 11:00 AM
> >     *To:* PostGIS Users Discussion
> >     *Subject:* [postgis-users] Divide 1 Polygon into 2 
> polygons with a
> >     linestring
> > 
> > 
> >     Hi,
> > 
> >     I have a problem. I have a polygon and a Linestring. 
> The linestring
> >     enters at one point the polygon and leaves at another. In other
> >     words, it goes through the polygon. I need to divide the polygon
> >     into two pieces, one right to the linestring and one left.
> > 
> >     Is there any method doing this? Can anyone help me? I 
> searched also
> >     in JTS package but I couldn't find anything.
> > 
> >     I 'll appreciate your help.
> > 
> >     Best Regards
> >     Baris
> > 
> >     
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