Patrice, Daniel,
Thank you for your commments - it shaded some light on the subject. Regards, André Mano 2012/2/5 Patrice Dumas <pertu...@free.fr> > On Sun, Feb 05, 2012 at 07:22:29AM -0200, Daniel Victoria wrote: > > Hi Andre, > > > > On raster algebra, operations using null will return null while > operations > > with 0 behaves like expected. Ex: > > 12 x null = null > > 12 x 0 = 0 > > Also means do not behave the same on NULL, for example when using r.univar > (according to my understanding of the documentation, haven't tested) > NULL cells are excluded from the computation, so 1 cell with a value 1 > and 9 NULL will give a mean of 1 while 1 cell with a value 1 and 9 with > value 0 will give a mean of 0.1. > > -- > Pat > _______________________________________________ > grass-user mailing list > grass-user@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/grass-user > -- --------------------------------------------------------------- Associação Leonel Trindade SOCIEDADE DE HISTÓRIA NATURAL Apartado 25 2564-909 Torres Vedras Portugal Sede e Biblioteca: rua Cavaleiros da Espora Dourada, 27A 2560 Torres Vedras Laboratório de Paleontologia e Paleoecologia: Polígono Industrial do Alto do Ameal 2565-641 Ramalhal http://alt-shn.blogspot.com www.alt-shn.org
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