Don't know who of you led me in the right direction, but eventually the line: "C=A + if(isnull(B),0,B)" in the manual solved my issue.
New_map = if(isnull(old_1),0,old_1) + if(isnull(old_2,0,old_2)) + etc and a following new_map=if(new_map>0,new_map,null()) I had four maps in my case, and that is why "new_map = if(!isnull(old_1) && !isnull(old_2), old_1+old_2, if(!isnull(old_1) && isnull(old_2), old_1, etc)" would become to long (4!=24 statements?) Thank you both Johannes and Moritz. Martin -----Opprinnelig melding----- Fra: Johannes Radinger [mailto:[email protected]] Sendt: 14. april 2011 15:13 Til: Martin Album Ytre-Eide; [email protected] Kopi: [email protected] Emne: Re: SV: [GRASS-user] Raster addition -------- Original-Nachricht -------- > Datum: Thu, 14 Apr 2011 14:31:32 +0200 > Von: Martin Album Ytre-Eide <[email protected]> > An: \'Moritz Lennert\' <[email protected]> > CC: "[email protected]" <[email protected]> > Betreff: SV: [GRASS-user] Raster addition > I would like the NULL values that overlap with none NULL values to be > treated as 0, and still have NULL values where both maps have NULL > values. The combined map would be a large map with NULL values and added > values. that is possible with the r.mapcalc and a if condition like: if(map A &&& map B, 0, null()) something like that (untested) might work. the null () provides NULL values where the condition is false. The triple &&& is the logic and (treats NULL values different from double &&). see: http://grass.fbk.eu/gdp/html_grass64/r.mapcalc.html for more information. /j > > Maybe the best way is to use r.null and set NULL values to 0. Add the > maps and then convert the 0 values to NULL values? > Or could one set the value in the if statement to be a the sum of maps > somehow? I guess my biggest problem is summing with NULL values - > maybe there is a way to treat NULL values as 0? I'll have a look at > the man page > > Thanks, > > Martin > > -----Opprinnelig melding----- > Fra: Moritz Lennert [mailto:[email protected]] > Sendt: 14. april 2011 14:15 > Til: Martin Album Ytre-Eide > Kopi: [email protected] > Emne: Re: [GRASS-user] Raster addition > > On 14/04/11 13:54, Martin Album Ytre-Eide wrote: > > Hello. > > > > I am trying to add some raster maps. I thought I could do this in > > r.mapcalc, but "new_map= old_1 + old_2" seems to produce a map where > > the maps overlap and ignoring areas where only on of the maps have > > values. > > This is due to the way r.mapcalc handles NULL values. See the man > page, section NULL support for an explanation. > > > I would like to do something similar to "v.overlay operator=or". > > > > Anyone who knows how to do this? > > It depends on what you want the new map to contain as values. If you > want to add the value of old_1 to old_2 in places where they overlap, > one way would be to transform your null values to 0 using r.null null= > and then applying your formula. > > If you just want a (any) value where one of the maps is non-null, then > you can use if. Something like this (untested): > > new_map = if(!isnull(old_1) || !isnull(old_2), 1, null()) > > which should give you 1 where any of the two contains a value and a > NULL value elsewhere. > > Moritz > _______________________________________________ > grass-user mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/grass-user -- GMX DSL Doppel-Flat ab 19,99 Euro/mtl.! Jetzt mit gratis Handy-Flat! http://portal.gmx.net/de/go/dsl _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
