Ok. I was worried there was something genious about your suggestion that I could not grasp :)
Andreas 2013/6/24 Kim Bisgaard <[email protected]> > Hi, > > You are right, I mistook ST_intersects() for ST_intersection() - me > butting out of this thread.. > > Regards, > Kim > > > On 2013-06-23 10:46, Andreas Forø Tollefsen wrote: > > Thanks for your answers. > > > Kim: We do not directly use ST_Intersection in our script, but ST_Clip to > clip the raster according to our polygons, and only where they > ST_Intersects(), not ST_Intersection(); > I still do not understand your suggestion. > > Best, > Andreas > > 2013/6/18 Kim Bisgaard <[email protected]> > >> Hi, >> >> Because ST_Intersection() returns neighbour pixels sharing a same value >> as only one >> polygon. You thus get a bigger area and thus more points. >> >> Bit me once :-/ >> >> Regards, >> Kim >> >> >> >> >> >> On 2013-06-18 14:59, Andreas Forø Tollefsen wrote: >> >> Hi Kim, >> >> Thanks for your answer. However, we want raster as an output, since we >> want to be able to use the summarystats function. >> Please elaborate how you think ST_PixelAsPolygons should solve out issue? >> Thanks. >> >> Andreas >> >> 2013/6/18 Kim Bisgaard <[email protected]> >> >>> Hi, >>> >>> Try to use 'ST_PixelAsPolygons(ST_Clip(n.rast, p.cell))' >>> instead of 'ST_Intersects(n.rast, p.cell)' >>> >>> Regards, >>> Kim >>> >>> >>> On 2013-06-18 11:03, Andreas Forø Tollefsen wrote: >>> >>> Hi, >>> >>> We are working on a raster summarystats script to calculate various >>> statistics for the pixels within fishnet polygons. >>> >>> Our raster cell size is 0.0083333333333... x 0.0083333333333... >>> degrees while our quadrat polygons are 0.5 x 0.5 decimal degrees. >>> This should give us 60x60 raster pixels within each of our polygons. >>> ArcGIS zonal statistics returns a pixel count of 3600 in addition to other >>> statistics. >>> However, PostGIS returns 3721 pixel count. >>> >>> We do not really understand why, but it seems that our query includes >>> some pixels that are outside of the polygon, but still touches the vertices >>> of the polygon and are therefore included in the calculation. >>> Are there any way of modifying our script to return the same result as >>> ArcGIS? >>> Thanks! >>> >>> Andreas >>> >>> script: >>> >>> /* This query makes one raster for each PRIO-GRID cell. Clip and union >>> is the procedure. */ >>> INSERT INTO nightlightsprio (gid, "year", rast) >>> (SELECT gid, "year", ST_Union(raster) as rast >>> FROM >>> (SELECT p.gid, n."year", ST_Clip(n.rast, p.cell) as raster >>> FROM nightlights n, priogridyear p >>> WHERE ST_Intersects(n.rast, p.cell) >>> AND n."year" = p."year" >>> ) >>> as priorast >>> GROUP BY gid, "year"); >>> >>> >>> /* Default BandNoDataValue is 0. Raster value 0 means no light, not no >>> data. Setting to NULL. This produces correct results. */ >>> UPDATE nightlightsprio2 SET rast = ST_SetBandNoDataValue(rast, 1, NULL); >>> >>> >>> ALTER TABLE nightlightsprio2 ADD COLUMN nightlights_sum double >>> precision, >>> ADD COLUMN nightlights_mean double precision, >>> ADD COLUMN nightlights_sd double precision, >>> ADD COLUMN nightlights_min double precision, >>> ADD COLUMN nightlights_max double precision, >>> ADD COLUMN nightlights_count integer; >>> >>> UPDATE nightlightsprio2 SET nightlights_sum = >>> (ST_SummaryStats(rast)).sum; >>> UPDATE nightlightsprio2 SET nightlights_mean = >>> (ST_SummaryStats(rast)).mean; >>> UPDATE nightlightsprio2 SET nightlights_sd = >>> (ST_SummaryStats(rast)).stddev; >>> UPDATE nightlightsprio2 SET nightlights_min = >>> (ST_SummaryStats(rast)).min; >>> UPDATE nightlightsprio2 SET nightlights_max = >>> (ST_SummaryStats(rast)).max; >>> UPDATE nightlightsprio2 SET nightlights_count = >>> (ST_SummaryStats(rast)).count; >>> >>> >>> >>> _______________________________________________ >>> postgis-users mailing >>> [email protected]http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users >>> >>> >>> -- >>> Kim Bisgaard >>> >>> Application Development Division Phone: +45 3915 7562 (direct) >>> Danish Meteorological Institute Fax: +45 3915 7460 (division) >>> >>> >>> _______________________________________________ >>> postgis-users mailing list >>> [email protected] >>> http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users >>> >>> >> >> >> _______________________________________________ >> postgis-users mailing >> [email protected]http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users >> >> >> -- >> Kim Bisgaard >> >> Application Development Division Phone: +45 3915 7562 (direct) >> Danish Meteorological Institute Fax: +45 3915 7460 (division) >> >> >> _______________________________________________ >> postgis-users mailing list >> [email protected] >> http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users >> >> > > > _______________________________________________ > postgis-users mailing > [email protected]http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users > > > -- > Kim Bisgaard > > Application Development Division Phone: +45 3915 7562 (direct) > Danish Meteorological Institute Fax: +45 3915 7460 (division) > > > _______________________________________________ > postgis-users mailing list > [email protected] > http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users > >
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