Hola Leo! You should use t.rast.algebra ( https://grass.osgeo.org/grass71/manuals/t.rast.algebra.html) from GRASS GIS 7.1 for that kind of temporal algebra operation. The command should be like:
t.rast.algebra expression="ndvi_a = ndvi[1] - ndvi[0]" basename=ndvi_a For more examples on temporal modules, you can see: https://grasswiki.osgeo.org/wiki/Temporal_data_processing HTH, Vero 2015-08-27 9:52 GMT-03:00 Leonardo Hardtke <[email protected]>: > Dear GRASS users: > I'm experienced grass user... I use GRASS since I started my PhD research > in landscape ecology back in 2009... > I'm trying to calculate the difference of NDVI between consecutive dates. > I used to do it like: > > i=0 > for map in $(g.list rast pattern=MOD13Q1*_01_*); do > NDVI[i]=$map > echo "Adding: " $map > let i=i+1 > done > > for id in $(seq 0 $(echo ${#NDVI[@]})); do > echo $id > r.mapcalc "ndvi_dif2_$id = ${NDVI[$id+1]} - ${NDVI[id]}" > done > > But i thing there must be an easier way using the grass 7 temporal > framework. So i registred my dataset and tried the following.... > > t.rast.list input=ndvi@ts > MOD13Q1.A2009001.h12v12.005.2009019145228_01_4326|ts|2009-01-01 > 00:00:00|2009-01-17 00:00:00 > MOD13Q1.A2009017.h12v12.005.2009035110230_01_4326|ts|2009-01-17 > 00:00:00|2009-02-02 00:00:00 > > ............................................................................................ > MOD13Q1.A2010337.h12v12.005.2010355100650_01_4326|ts|2010-12-03 > 00:00:00|2010-12-19 00:00:00 > MOD13Q1.A2010353.h12v12.005.2011005202724_01_4326|ts|2010-12-19 > 00:00:00|2011-01-04 00:00:00 > > > t.rast.mapcalc input=ndvi expression="ndvi[1] - ndvi[0]" output=ndvi_a > basename=ndvi_a > > But the output is not good (see attached file: left is OK, rigth is wrong) > Am I doing something wrong? > Thanks! > Dr. Leonardo A. Hardtke > Laboratorio de Teledetección y S.I.G. > Centro Nacional Patagónico (CONICET) > Bvd. Brown 2825, 9120 > Puerto Madryn, Chubut, Argentina > > _______________________________________________ > grass-user mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/grass-user >
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