Re: [postgis-users] raster regions

[Pierre Racine]

Right. To minimize the amount of intermediate computation you can add a 
discriminant to the first query:

WITH floodareas AS (
  SELECT ST_MapAlgebra(rast, ‘1BB’, ‘CASE WHEN [rast] < 10 THEN 1 ELSE NULL 
END’) rast
  FROM elevation e, districts d
  WHERE ST_Intersects(d.geom, e.rast)
)
SELECT d.*
FROM districts d, floodareas f
WHERE ST_Intersects(d.geom, f.rast)

Pierre
De : postgis-users <postgis-users-boun...@lists.osgeo.org> De la part de 
joao.corde...@inpe.br
Envoyé : 15 juillet 2019 14:40
À : postgis-users@lists.osgeo.org
Objet : Re: [postgis-users] raster regions


Thanks, Pierre,

It seems ok to model the query the way you showed, however, that implies the 
generation of an entire intermediate binary raster, just to identify the region 
inside the whole mapped area. My issue is on avoiding such intermediate data by 
incorporating map algebra expression into the same query expression, Another 
example, ""... d.geom touch (ndvi2018 < ndvi2019)" where ndvixxxx are raster 
data.

Att.

Em 15-07-2019 14:43, Pierre Racine escreveu:
Hi,

That could translate into something like this in PostGIS:

WITH floodareas AS (
  SELECT ST_MapAlgebra(rast, ‘1BB’, ‘CASE WHEN [rast] < 10 THEN 1 ELSE NULL 
END’) rast
  FROM elevation
)
SELECT d.*
FROM districts d, floodareas f
WHERE ST_Intersects(g.geom, f.rast)

NULL becomes nodata values. You could also use ST_Reclass() instead of 
ST_Mapalgebra().

Pierre

De : postgis-users 
<postgis-users-boun...@lists.osgeo.org<mailto:postgis-users-boun...@lists.osgeo.org>>
 De la part de Joao Cordeiro
Envoyé : 15 juillet 2019 10:19
À : 'PostGIS Users Discussion' 
<postgis-users@lists.osgeo.org<mailto:postgis-users@lists.osgeo.org>>
Objet : [postgis-users] raster regions


Hi there,

I am not actually a POSTGIS user, or developer, although I am doing some 
research of integration of vector -raster in a dbms context. My main question s 
about identifying regions represented in a domain like the "hybrid raster" so 
that they can be referred to in a query. For example, I would like to write 
something like "select d from districts where d.geometry touches flooding", 
where "flooding" indicates an expression intended to decide on the pertinence 
of locations to a flooding ​​risk area described, for instance through map 
algebra.

Thanks for any hints or suggestions.

Att.


_______________________________________________

postgis-users mailing list

postgis-users@lists.osgeo.org<mailto:postgis-users@lists.osgeo.org>

https://lists.osgeo.org/mailman/listinfo/postgis-users




_______________________________________________
postgis-users mailing list
postgis-users@lists.osgeo.org
https://lists.osgeo.org/mailman/listinfo/postgis-users