[postgis-users] Creating a boundary of an aggregate of buildings

[Luca Bertoncello]

Am 18.01.2021 12:48, schrieb Tomas Straupis:

Hi Tomas,

>   Are you sure you're getting a combined multigeometry before applying
> buffer+-? All small polygons which you expect to be aggregated into
> one should be in one geometry (one row) before doing buffering.

No, I'm not... :) Sorry, I'm really a beginner with PostGIS and 
OpenStreetMaps...

>   1. Increase buffer size.
>   2. ST_ConvexHull, ST_ConcaveHull.
> 
>   Here is a working forest aggregation routine.
> 
> create table gen_forest as
>   select nextval('gen_forest_seq') AS id
>         ,0::bigint AS way_area
>         ,10 AS res
>         ,ST_CollectionExtract(unnest(ST_ClusterWithin(way, 10)),
> 3)::geometry(MultiPolygon, 3857) as way
>     from planet_osm_polygon
>    where landuse = 'forest';
> 
> delete from gen_forest where st_area(st_buffer(way, -10)) < 10 and res 
> = 10;
> 
> update gen_forest set way =
> st_makevalid(st_multi(st_simplifypreservetopology(st_buffer(st_buffer(way,
> 10, 'quad_segs=1'), -10, 'quad_segs=1'), 10))) where res = 10;
> update gen_forest set way_area = st_area(way) where res = 10;

I'll try to create a table with landuse = 'residential' (and the other), 
then use this table to generate the boundaries...
Do I understand correctly, you create areas with "forests" and distance 
not greater than 10 meters?

I'll report to the list the result.

Thanks
Luca Bertoncello
(lucabert at lucabert.de)