[postgis-users] Raster pixel value

[Pierre Racine]

I have put a first version of ST_Clip in script/plpgsql

Pierre

> -----Original Message-----
> From: postgis-users-bounces at postgis.refractions.net [mailto:postgis-users-
> bounces at postgis.refractions.net] On Behalf Of Tom van Tilburg
> Sent: Thursday, December 01, 2011 7:14 AM
> To: postgis-users at postgis.refractions.net
> Subject: Re: [postgis-users] Raster pixel value
> 
> Pierre,
> 
> This is great you're working on this. It is exactly what I think that pgraster is
> going to make a great tool.
> 
> Last days I didn't really have time to check out things, hopefully this week.
> 
> Cheers,
>   Tom
> 
> On 30-11-2011 19:19, Pierre Racine wrote:
> > Andreas, Tom,
> >
> > I have put two new functions you might be interested by in
> >
> > http://trac.osgeo.org/postgis/browser/trunk/raster/scripts/plpgsql
> >
> > The first one, st_areaweightedsummarystats.sql, is usefull when you want
> to compute summary stats (like the weighted mean) of values coming from
> a raster table for a series of polygons and that you use
> ST_Intersection(raster, geometry) to compute the intersection. You
> normally use it this way:
> >
> > SELECT gt.id,
> >         (aws).count,
> >         (aws).distinctcount,
> >         (aws).geom,
> >         (aws).totalarea,
> >         (aws).meanarea,
> >         (aws).totalperimeter,
> >         (aws).meanperimeter,
> >         (aws).weightedsum,
> >         (aws).weightedmean,
> >         (aws).maxareavalue,
> >         (aws).minareavalue,
> >         (aws).maxcombinedareavalue,
> >         (aws).mincombinedareavalue,
> >         (aws).sum,
> >         (aws).mean,
> >         (aws).max,
> >         (aws).min
> > FROM (SELECT ST_AreaWeightedSummaryStats(gv) aws
> >        FROM (SELECT ST_Intersection(rt.rast, gt.geom) gv
> >              FROM rasttable rt, geomtable gt
> >              WHERE ST_Intersects(rt.rast, gt.geom)
> >             ) foo
> >        GROUP BY gt.id
> >       ) foo2
> >
> > The second one, st_summarystatsagg.sql, serve the same purpose but
> when you are using ST_MapAlgebra() (soon ST_Clip()) to compute the
> intersection. you normally use it like this:
> >
> > SELECT (ss).count,
> >         (ss).sum,
> >         (ss).mean,
> >         (ss).min,
> >         (ss).max
> > FROM (SELECT ST_SummaryStatsAgg(gv) ss
> >        FROM (SELECT ST_Clip(rt.rast, gt.geom) gv
> >              FROM rasttable rt, geomtable gt
> >              WHERE ST_Intersects(rt.rast, gt.geom)
> >             ) foo
> >        GROUP BY gt.id
> >       ) foo2
> >
> > This is very equivalent to what you were doing. The ST_Clip() replace the
> ST_MapAlgebra() part and the ST_SummaryStatsAgg() replace the
> ST_SummaryStats(ST_Union())  part. This should be faster since it does a
> ST_Union() less.
> >
> > I'm working on a plpgsql version of ST_Clip(). I will post it very soon.
> >
> > Pierre
> >
> > _______________________________________________
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> > postgis-users at postgis.refractions.net
> > http://postgis.refractions.net/mailman/listinfo/postgis-users
> 
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