[postgis-users] Open buffers or parallel lines

iirc a.neumann at carto.net
Wed Jun 17 04:26:50 EDT 2009


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.


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;
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