> I am trying to reclassify a slope surface with a reverse normalisation (lower > the > slope value, the closer to 1 it becomes). > > It can be done in ArcGIS in the Raster Calculator using: > (0.404234915971756 - "slope") / 0.404234915971756 where > 0.404234915971756 is the maximum value (minimum value of the data is zero so > I don't need to include this in the calculation). > > Wanting to recreate this process in PostGIS so can anyone advise on how I > could > do the calculation for: > (max. value - cell value)/ max. value for each cell in the raster? > Cannot get my head around it.
1) Compute the slope with ST_Slope() 2) Determine the max slope value with ST_SummaryStat() 3) Normalize with ST_MapAlgebraExpr() You can eventually do all that in one complex query. And read the doc: http://postgis.refractions.net/documentation/manual-svn/RT_reference.html Pierre _______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users