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

[Luca Bertoncello]

Am 27.01.2021 22:07, schrieb Luca Bertoncello:

Hi list

> derived from what you suggested
> 
>> -- Aggregates all clustered polygons by adding 120m and then removing
>> 120m from all sides
>> UPDATE city_boundaries SET way =
>> ST_Makevalid(ST_Multi(ST_Buffer(ST_Buffer(way, 120, 'join=miter'),
>> -120, 'join=miter'))) WHERE res = 10;
> 
> runs since today ~13:30 (8,5 hours).
> Do you/do someone have an idea how to speed it up? The PC has 4 cores
> and 16 GB RAM and currently I cannot add more RAM.

I found what uses the huge amount of RAM:

gis=# select char_length(way) from city_boundaries where id = 25822;
  char_length
-------------
      2252882

So a very huge polygon...
And if I check the other polygons for Europe, I see:

gis=# select count(*) from city_boundaries where char_length(way) > 
100000;
  count
-------
    675
(1 Zeile)

gis=# select count(*) from city_boundaries where char_length(way) > 
1000000;
  count
-------
     45
(1 Zeile)

Maybe is there any other possibility to aggregate the huge polygons 
reducing the used RAM?

Thanks
Luca Bertoncello
(lucabert at lucabert.de)