[postgis-users] Raster pixel value

[Andreas Forø Tollefsen]

This is great! Fantastic. I will do some testing.

2011/12/1 Tom van Tilburg <tom.van.tilburg at gmail.com>

> 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<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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