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ST_MapAlgebraExpr — 1 raster band version: Creates a new one band raster formed by applying a valid PostgreSQL algebraic operation on the input raster band and of pixeltype provided. Band 1 is assumed if no band is specified.
raster ST_MapAlgebraExpr(raster rast, integer band, text pixeltype, text expression, double precision nodataval=NULL);
raster ST_MapAlgebraExpr(raster rast, text pixeltype, text expression, double precision nodataval=NULL);
ST_MapAlgebraExpr is deprecated as of 2.1.0. Use ST_MapAlgebra (expression version) instead.
Creates a new one band raster formed by applying a valid PostgreSQL algebraic operation defined by the expression on the input raster (rast). If no band is specified band 1 is assumed. The new raster will have the same georeference, width, and height as the original raster but will only have one band.
If pixeltype is passed in, then the new raster will have a band of that pixeltype. If pixeltype is passed NULL, then the new raster band will have the same pixeltype as the input rast band.
In the expression you can use the term [rast] to refer to the pixel value of the original band, [rast.x] to refer to the 1-based pixel column index, [rast.y] to refer to the 1-based pixel row index.
Create a new 1 band raster from our original that is a function of modulo 2 of the original raster band.
ALTER TABLE dummy_rast ADD COLUMN map_rast raster; UPDATE dummy_rast SET map_rast = ST_MapAlgebraExpr(rast,NULL,'mod([rast]::numeric,2)') WHERE rid = 2; SELECT ST_Value(rast,1,i,j) As origval, ST_Value(map_rast, 1, i, j) As mapval FROM dummy_rast CROSS JOIN generate_series(1, 3) AS i CROSS JOIN generate_series(1,3) AS j WHERE rid = 2; origval | mapval ---------+-------- 253 | 1 254 | 0 253 | 1 253 | 1 254 | 0 254 | 0 250 | 0 254 | 0 254 | 0
Create a new 1 band raster of pixel-type 2BUI from our original that is reclassified and set the nodata value to be 0.
ALTER TABLE dummy_rast ADD COLUMN map_rast2 raster; UPDATE dummy_rast SET map_rast2 = ST_MapAlgebraExpr(rast,'2BUI'::text,'CASE WHEN [rast] BETWEEN 100 and 250 THEN 1 WHEN [rast] = 252 THEN 2 WHEN [rast] BETWEEN 253 and 254 THEN 3 ELSE 0 END'::text, '0') WHERE rid = 2; SELECT DISTINCT ST_Value(rast,1,i,j) As origval, ST_Value(map_rast2, 1, i, j) As mapval FROM dummy_rast CROSS JOIN generate_series(1, 5) AS i CROSS JOIN generate_series(1,5) AS j WHERE rid = 2; origval | mapval ---------+-------- 249 | 1 250 | 1 251 | 252 | 2 253 | 3 254 | 3 SELECT ST_BandPixelType(map_rast2) As b1pixtyp FROM dummy_rast WHERE rid = 2; b1pixtyp ---------- 2BUI
Create a new 3 band raster same pixel type from our original 3 band raster with first band altered by map algebra and remaining 2 bands unaltered.
SELECT ST_AddBand( ST_AddBand( ST_AddBand( ST_MakeEmptyRaster(rast_view), ST_MapAlgebraExpr(rast_view,1,NULL,'tan([rast])*[rast]') ), ST_Band(rast_view,2) ), ST_Band(rast_view, 3) ) As rast_view_ma FROM wind WHERE rid=167;