[Qgis-user] PostGIS Polygon Editing

[pcreso at pcreso.com]

Set QGIS snapping on, so the new points will be "snapped" to the nearest existing one within an appropriate tolerance.


The other way to do this in Postgis is using topology, add all your component linestrings & let Postgis build the faces/polygons from this. So shared boundaries are the same linestring, not a separate one, ensuring the polygon edges are identical.

See this example:
http://trac.osgeo.org/postgis/wiki/UsersWikiTopologyExample

& the full docs:
http://trac.osgeo.org/postgis/wiki/UsersWikiPostgisTopology
http://postgis.refractions.net/docs/Topology.html


Cheers,

  Brent Wood


--- On Thu, 11/8/12, uk52rob <uk52rob at yahoo.co.uk> wrote:

From: uk52rob <uk52rob at yahoo.co.uk>
Subject: [Qgis-user] PostGIS Polygon Editing
To: "qgis-user at lists.osgeo.org" <qgis-user at lists.osgeo.org>
Date: Thursday, November 8, 2012, 10:07 PM

Hi,
I have a PostGIS polygon layer in QGIS which I need to add features to.
I can add polygons to it, no problem, but I need to be able to have the edges of the new features lined up exactly with the existing features. This is essentially to fill a void in the layer, or to continue in one direction. I have done this
 before using local shapefiles and the difference tool (very time consuming!), but this requires separate layers. 
Is it possible to achieve the same result with a single PostGIS layer, so I can overlap an existing feature with my new feature, and trim it to the existing feature's boundary?
I hope this makes sense!
Thanks
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