[postgis-users] PostGIS Raster Area from a Clip

[Marcello Benigno]

Just complementing ...

In my case there is no overlap in any of the layers, there really was no
need ST_Union.

Thanks again for the help and the discussion.

Regards,


2013/10/22 Pierre Racine <Pierre.Racine at sbf.ulaval.ca>

> > Won't that only yield the same answer if you can guarantee no overlapping
> > geometries in the fazendas table? My understanding was that the other
> > table was the raster table (which it is reasonable to assume has no
> > overlaps), but we don't know if that's the case with this one.
>
> Right. But you generally have to have a minimal knowledge about the
> topology of a layer when you query it. Querying a layer with overlaps is
> never the same as querying a layer without.
>
> So if you know your fazendas layer has overlaps it is a good idea to use
> ST_Union but that means you are getting stats about the global farming area
> not about each farming area. What about areas overlapping? Should they
> count twice? Do these overlaps make sense in reality? Maybe you have to fix
> then first...
>
> Pierre
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-- 
*Marcello Benigno B. de Barros Filho*
Prof. do Curso Superior de Tecnologia em Geoprocessamento - IFPB
Mestre em Ciências Geodésicas e Tecnologias da Geoinformação - UFPE
Doutorando em Tecnologia Ambiental e Recursos Hídricos - UFPE
http://profmarcello.blogspot.com
http://about.me/marcello.benigno
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