[postgis-users] raster, stats conditioned to a set of values

[Pierre Racine]

You can select pixels fulfilling an expression using the one-raster variant of ST_MapAlgebra

http://postgis.net/docs/RT_ST_MapAlgebra_expr.html

So just do something like:

ST_MapAlgebra(rast, '8BUI'::text, '[rast] > 0')

before computing stats.

To count the number of pixels of a certain value you can use ST_ValueCount().

Pierre

> -----Original Message-----
> From: postgis-users-bounces at lists.osgeo.org [mailto:postgis-users-
> bounces at lists.osgeo.org] On Behalf Of juli g. pausas
> Sent: Monday, June 29, 2015 12:49 PM
> To: PostGIS Users Discussion
> Subject: [postgis-users] raster, stats conditioned to a set of values
> 
> Hi all
> 
> I'm just starting to discover postgis, it is really useful.
> 
> I have a raster file with different bands, that I have imported to postgres
> (raster2pgsql, without the -R option, i.e., insite the database). I would like to
> extract information from band 1, but filtering the data using only
> 
> 1) pixels with positive values (in that band, band 1)
> 
> 2) and pixels in which band 2 is equal to a given value, e.g. 1
> 
> 
> The type of analysis I'd like to do is descriptive stats but also intersecting
> with a vector map. If my raster is rastertmp.ndvitmp, two examples are:
> 
> 
> SELECT (ST_SummaryStats(rast, 1)).* FROM rastertmp.ndvitmp WHERE rid
> = 1
> 
> 
> 
> SELECT p.region_cod, ST_ValueCount(ST_Clip(r.rast,1, p.geom, true)) AS res
>   FROM gis_wd.wd_regiones AS p, rastertmp.ndvitmp AS r
>   WHERE ST_Intersects(r.rast, p.geom)
>   AND p.region_cod = 'PA1214';
> 
> 
> 
> This works perfectly, but how can I compute the stats  only for pixels with
> positive values and with a given value in another band?  The idea would be
> something like:  WHERE ST_Values(rast, 1)>0 AND ST_Values(rast, 2)=1
> 
> 
> Thanks for any help!
> 
> 
> Juli
> --
> CIDE, CSIC  |  www.uv.es/jgpausas  |
>