Though this is probably possible in PostGIS nowadays I would personally solve such a use case with GMT (http://gmt.soest.hawaii.edu/), for example with grdmath (http://gmt.soest.hawaii.edu/doc/5.2.1/grdmath.html) which lets you perform rather complex computations on multiple grids (for examples rasters) using reverse polish notation.
-ra On 23 Nov 2015, at 13:20, Darrel Maddy <darrel.ma...@newcastle.ac.uk> wrote: > Dear all, > > As you know I am relatively new to postgis and SQL and therefore I have much > to learn. However, I am facing a paper deadline and need to do some quick > analysis of the data I have and I am struggling to figure out how best to > pursue what I need to do. > > I have a significant number of rasters which have double precision values. > Without going into detail about what the rasters represent, I need to extract > and sum values from one set of rasters in say table A based upon values in > another set of rasters in say table B where the pixel value in the raster > from Table B exceeds a threshold. Both tables are the same size (rasters are > tiled) but I also need to figure out how I make sure the correct rasters are > compared. They have filenames like this rastervariable_10.tif, > rastervariable_100.tif , presumably I need to use a logical expression to > strip the numerical value (in this case this represents the year) and then > order on that basis? > > I can do this in QGIS one at a time but that is a little clumsy and rather > time consuming. > > If someone can just point me in the right direction I am sure I can figure > out the rest for myself. > > Apologies once more for asking what is probably a rather trivial question and > yet again demonstrating my ignorance. > > Many thanks > > Darrel > _______________________________________________ > postgis-users mailing list > postgis-users@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/postgis-users
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