[postgis-users] PostGIS Topology Pledge: completed !

[Ben Madin]

Thanks strk,

this is great news - thank you for your efforts,

cheers

Ben


On 30/01/2012, at 7:49 PM, Sandro Santilli wrote:

> As of revision 8963 (included in upcoming 2.0.0alpha3 [1]), the function
> to convert simple layers to topologically defined layers [2] is completed.
> 
> [1] 2.0.0alpha3 http://www.postgis.org/download/
> [2] toTopoGeom http://trac.osgeo.org/postgis/ticket/1017
> 
> This means that building a persistent topology for your public.states.geom
> layer would be as simple as this:
> 
> SELECT CreateTopology('states_topo');
> SELECT AddTopoGeometryColumn('states_topo',
>                              'public', 'states', 'topogeom',
>                              'POLYGON');
> UPDATE public.states
>   SET topogeom = toTopoGeom(geom, 'states_topo');
> 
> You can then check correctness of the conversion:
> 
> SELECT gid FROM public.states WHERE NOT ST_Equals(geom, topogeom);
> 
> Look for area overlaps:
> 
> SELECT r1.element_id FROM states_topo.relation r1, states_topo.relation r2
> WHERE r1.topogeo_id != r2.topogeo_id AND r1.element_id = r2.element_id;
> 
> Or underlaps:
> 
> SELECT face_id FROM istat_topo.face WHERE face_id > 0
> AND face_id NOT IN ( SELECT element_id FROM istat_topo.relation );
> 
> Perform any editing required to clean things up [3], or to simplify the edges.
> You can take a look at the primitives with QGIS db_manager plugin [4], or even
> at the actual TopoGeometries with QGIS master [5] (although it will be slow in
> selecting features within the viewport, see ticket #1290 [6]).
> 
> [3] http://strk.keybit.net/blog/2011/11/21/topology-cleaning-with-postgis/
> [4] qgis db_manager http://www.qgis.org/wiki/DB_Manager_plugin_GSoC_2011
> [5] QuantumGIS http://www.qgis.org
> [6] overlap TopoGeometry http://trac.osgeo.org/postgis/ticket/1290
> 
> And of course you can convert TopoGeometries back to simple geometries when needed
> for performance or compatibility reasons:
> 
> ALTER TABLE public.states ADD newgeom geometry;
> UPDATE public.states SET newgeom = topogeom::geometry;
> 
> Happy edge walking!
> http://strk.keybit.net/blog/2012/01/28/a-walk-on-the-wild-side/
> 
> --------------------------------
>  C L O S I N G    C R E D I T S
> --------------------------------
> 
> I was able to dedicate my time to the implementation of the toTopoGeom
> function thanks to the contribution of a disparate group of people and
> companies putting a part of the money each to reach the bigger target:
> 
>   Andrea Peri            Anne Ghisla               R3 GIS
>   Silvio Grosso          GFOSS (gfoss.it)          Cooperativa Alveo
>   AusVet                 Ingvild Nystuen           Luca S. Percich
>   Richard Greenwod       Andreas Neumann           Oslandia
> 
> A special thank goes to Andrea Peri for his initial kick-starter contribution
> which allowed me to set an affordable target for the pledge.
> 
> Also thanks to the Geographical Free and Open Source Software association
> (GFOSS) for the help with reducing paperwork involved in handling all the
> contributions.
> 
> --strk;
> 
>  ,------o-. 
>  |   __/  |    Thank you for PostGIS-2.0 Topology !
>  |  / 2.0 |    http://www.pledgebank.com/postgistopology
>  `-o------'
> 
> _______________________________________________
> postgis-users mailing list
> postgis-users at postgis.refractions.net
> http://postgis.refractions.net/mailman/listinfo/postgis-users



-- 

Ben Madin

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