[postgis-users] Simplify a perfect (hierarchical) partition of polygons (ST_SimplifyPreserveTopology and friends)

[William Humphrey Temperley]

> -----Original Message-----
> From: postgis-users-bounces at postgis.refractions.net [mailto:postgis-users-
> bounces at postgis.refractions.net] On Behalf Of Martin Tomko
> Sent: 14 March 2012 01:20
> To: postgis-users at postgis.refractions.net
> Subject: Re: [postgis-users] Simplify a perfect (hierarchical) partition
of
> polygons (ST_SimplifyPreserveTopology and friends)
> 
 
> I think that the best way for this hierarchical scenarios is to start from
the
> finest geographies and aggregate upwards on the generalised ones. I will
> have to somehow control for the intermediate nodes that are not valid for
> higher order geometries (joins of suburbs on the state boundary, etcŠ),
but
> that I could solve somehow.
> 

Martin,

I recently did this for the Global Administrative Unit Layers (GAUL) stored
in PostGIS using the simplify polygon tools in ArcGIS.  Whilst I'd love to
use the new topology tools Sandro has developed, this wasn't practical at
this time.

The steps I took were:
1. Simplify the smallest (admin2) units using the Simplify Polygon tool,
asking it to resolve topological errors.
2. Dissolve the generalized polygons on their parent id 
3. Repeat 2 until I arrived at admin0 

Each time I had to reload the new geometries back into PostGIS.

HTH,

Will Temperley
Spatial Database Developer
Land Resource Management Unit
European Commission - Joint Research Centre