Open buffers or parallel lines
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Open buffers or parallel lines
by Andreas Neumann-7
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Hi all,
I am looking for either a "parallel line" feature or "open buffers around a linestring element". The idea is to visualize a waste-water system where in large map scales the actual diameter of the waste-water pipes (canalization). The linecaps shouldn't be stroked, but the parallel offset to the centerline should be drawn. Are there any tricks how this can be done in Postgis? I see that there is st_buffer, but there is no option to get an open buffer or parallel lines. Thanks for any hints, Andreas -- Andreas Neumann http://www.carto.net/neumann/ http://www.svgopen.org/ _______________________________________________ postgis-users mailing list postgis-users@... http://postgis.refractions.net/mailman/listinfo/postgis-users |
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Re: Open buffers or parallel lines
by Regina Obe
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This might help
http://trac.osgeo.org/postgis/wiki/UsersWikiplpgsqlfunctions upgis_lineshift(centerline geometry, dist double precision) Though its simplified in the sense it bases on start and end points of the linestring to do the shift. To do true shifting when you have very curvy lines or polygons - you'd probably want to use Simon's approach. http://www.spatialdbadvisor.com/postgis_tips_tricks/128/exploding-a-line string-or-polygon-into-individual-vectors-in-postgis/ (hmm I though he had that wrapped more nicely in a function, but can't find it). Hope that helps, Regina -----Original Message----- From: postgis-users-bounces@... [mailto:postgis-users-bounces@...] On Behalf Of Andreas Neumann Sent: Tuesday, June 16, 2009 7:53 AM To: PostGIS Users Discussion Subject: {SPAM: 40} :[postgis-users] Open buffers or parallel lines Hi all, I am looking for either a "parallel line" feature or "open buffers around a linestring element". The idea is to visualize a waste-water system where in large map scales the actual diameter of the waste-water pipes (canalization). The linecaps shouldn't be stroked, but the parallel offset to the centerline should be drawn. Are there any tricks how this can be done in Postgis? I see that there is st_buffer, but there is no option to get an open buffer or parallel lines. Thanks for any hints, Andreas -- Andreas Neumann http://www.carto.net/neumann/ http://www.svgopen.org/ _______________________________________________ postgis-users mailing list postgis-users@... http://postgis.refractions.net/mailman/listinfo/postgis-users ----------------------------------------- The substance of this message, including any attachments, may be confidential, legally privileged and/or exempt from disclosure pursuant to Massachusetts law. It is intended solely for the addressee. If you received this in error, please contact the sender and delete the material from any computer. _______________________________________________ postgis-users mailing list postgis-users@... http://postgis.refractions.net/mailman/listinfo/postgis-users |
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Re: Open buffers or parallel lines
by strk-2
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On Tue, Jun 16, 2009 at 01:52:33PM +0200, Andreas Neumann wrote:
> Hi all, > > I am looking for either a "parallel line" feature or "open buffers around > a linestring element". > > The idea is to visualize a waste-water system where in large map scales > the actual diameter of the waste-water pipes (canalization). The linecaps > shouldn't be stroked, but the parallel offset to the centerline should be > drawn. > > Are there any tricks how this can be done in Postgis? I see that there is > st_buffer, but there is no option to get an open buffer or parallel lines. See if what's currently referred to "Single-Sided-Buffer" and probably to become "Offset Curve" is what you're looking for. http://trac.osgeo.org/geos/ticket/215 --strk; Free GIS & Flash consultant/developer () ASCII Ribbon Campaign http://foo.keybit.net/~strk/services.html /\ Keep it simple! _______________________________________________ postgis-users mailing list postgis-users@... http://postgis.refractions.net/mailman/listinfo/postgis-users |
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Re: Open buffers or parallel lines
by Simon Greener-3
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Regina,
> This might help > > http://trac.osgeo.org/postgis/wiki/UsersWikiplpgsqlfunctions > > upgis_lineshift(centerline geometry, dist double precision) > > Though its simplified in the sense it bases on start and end points of > the linestring to do the shift. > > To do true shifting when you have very curvy lines or polygons - you'd > probably want to use Simon's approach. > > http://www.spatialdbadvisor.com/postgis_tips_tricks/128/exploding-a-line > string-or-polygon-into-individual-vectors-in-postgis/ > > (hmm I though he had that wrapped more nicely in a function, but can't > find it). I have it partially built. Am away consulting. Could finish it next week if Andreas is prepared to wait. S -- SpatialDB Advice and Design, Solutions Architecture and Programming, Oracle Database 10g Administrator Certified Associate; Oracle Database 10g SQL Certified Professional Oracle Spatial, SQL Server, PostGIS, MySQL, ArcSDE, Manifold GIS, FME, Radius Topology and Studio Specialist. 39 Cliff View Drive, Allens Rivulet, 7150, Tasmania, Australia. Website: www.spatialdbadvisor.com Email: simon@... Voice: +61 362 396397 Mobile: +61 418 396391 Skype: sggreener Longitude: 147.20515 (147° 12' 18" E) Latitude: -43.01530 (43° 00' 55" S) NAC:W80CK 7SWP3 _______________________________________________ postgis-users mailing list postgis-users@... http://postgis.refractions.net/mailman/listinfo/postgis-users |
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Re: Open buffers or parallel lines
by Andreas Neumann-7
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Hi,
Thanks Regina and Strk for your ideas. Yes, the single-sided buffers would probably solve my problem. Any predictions on why this patch will make it into the Postgis trunk? I assume it won't be possible for Postgis 1.4.0, but maybe for 1.4.1? Another requirement I have is getting full buffers around linestrings that would also offer the butt and square linecaps instead of just round linecaps. I initially thought to get this simulated by setting num_seg_quarter_circle to zero - but this doesn't work. It always introduces at least one vertex for the linecaps. Thanks, Andreas strk wrote: > On Tue, Jun 16, 2009 at 01:52:33PM +0200, Andreas Neumann wrote: > >> Hi all, >> >> I am looking for either a "parallel line" feature or "open buffers around >> a linestring element". >> >> The idea is to visualize a waste-water system where in large map scales >> the actual diameter of the waste-water pipes (canalization). The linecaps >> shouldn't be stroked, but the parallel offset to the centerline should be >> drawn. >> >> Are there any tricks how this can be done in Postgis? I see that there is >> st_buffer, but there is no option to get an open buffer or parallel lines. >> > > See if what's currently referred to "Single-Sided-Buffer" and probably > to become "Offset Curve" is what you're looking for. > > http://trac.osgeo.org/geos/ticket/215 > > --strk; > > Free GIS & Flash consultant/developer () ASCII Ribbon Campaign > http://foo.keybit.net/~strk/services.html /\ Keep it simple! > _______________________________________________ > postgis-users mailing list > postgis-users@... > http://postgis.refractions.net/mailman/listinfo/postgis-users > _______________________________________________ postgis-users mailing list postgis-users@... http://postgis.refractions.net/mailman/listinfo/postgis-users |
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Re: Open buffers or parallel lines
by Andreas Neumann-7
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sure - I can wait - it's not that urgent.
Let me know if there is something to test. Andreas Simon Greener wrote: > Regina, > > >> This might help >> >> http://trac.osgeo.org/postgis/wiki/UsersWikiplpgsqlfunctions >> >> upgis_lineshift(centerline geometry, dist double precision) >> >> Though its simplified in the sense it bases on start and end points of >> the linestring to do the shift. >> >> To do true shifting when you have very curvy lines or polygons - you'd >> probably want to use Simon's approach. >> >> http://www.spatialdbadvisor.com/postgis_tips_tricks/128/exploding-a-line >> string-or-polygon-into-individual-vectors-in-postgis/ >> >> (hmm I though he had that wrapped more nicely in a function, but can't >> find it). >> > > I have it partially built. Am away consulting. Could finish it next week if Andreas is prepared to wait. > > S > _______________________________________________ postgis-users mailing list postgis-users@... http://postgis.refractions.net/mailman/listinfo/postgis-users |
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Re: Open buffers or parallel lines
by strk-2
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On Wed, Jun 17, 2009 at 01:26:50PM +0200, iirc wrote:
> Hi, > > Thanks Regina and Strk for your ideas. > > Yes, the single-sided buffers would probably solve my problem. > > Any predictions on why this patch will make it into the Postgis trunk? I > assume it won't be possible for Postgis 1.4.0, but maybe for 1.4.1? > > Another requirement I have is getting full buffers around linestrings > that would also offer the butt and square linecaps instead of just round > linecaps. Offset curves are planned to get out with GEOS-3.2.0 around mid July. Butt and square linecaps are already implemented in geos-trunk. Both will need C-API exposure *and* postgis side of things to get into SQL. Those parts are not in the works. Patches or fundings are welcome. --strk; Free GIS & Flash consultant/developer () ASCII Ribbon Campaign http://foo.keybit.net/~strk/services.html /\ Keep it simple! _______________________________________________ postgis-users mailing list postgis-users@... http://postgis.refractions.net/mailman/listinfo/postgis-users |
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