[GRASSLIST:10527] Re: help with R and GRASS6

[Carlos "Guâno" Grohmann]

Well, I managed to get the residuals of the trend-surface analysis in a
Spatial data Frame.

Here's what I did:


library(spgrass6) ; library(spatial);
srtm <- getSites6sp("toposrtm");
coords<-coordinates(srtm);
class(srtm);
G <- gmeta6();
grd <- GridTopology(cellcentre.offset=c(G$west+(G$ewres/2),
G$south+(G$nsres/2)), cellsize=c(G$ewres, G$nsres), cells.dim=c(G$cols,
G$rows));
mask_SG <- SpatialGridDataFrame(grd, data=list(k=rep(1, G$cols*G$rows)),
proj4string=CRS(G$proj4));
class(mask_SG);

trend <- surf.ls(1, x=coords[,1], y=coords[,2], z=srtm$cat);
resid1<-residuals(trend);
resid2<-as.data.frame(resid1);
resid.trend<-SpatialPointsDataFrame(coords,resid2);
resid.img <- SpatialGridDataFrame(grd, resid.trend);



Now I'll start playing with variograms and kriggind.

Thanks all!

Carlos


On 2/21/06, Roger Bivand <Roger.Bivand at nhh.no> wrote:
>
> Hi Carlos,
>
> On Tue, 21 Feb 2006, Carlos "Guâno" Grohmann wrote:
>
> > Hello list
> >
> > I've away from R a while, and now I'm struggling with it...
> > I read Bivand's artile in GRASS-News3, but I dindn't understant exactly
> how
> > the data is stored in R.
> >
>
> Please see a note in R News in November 2005 by Edzer Pebesma and me.
>
> > If I want to make a trend-surface analysis with surf.ls(), I need the
> x,y
> > and z coordinates of each point (or pixel), but I don't know how to get
> > these values
>
> The object returned by getSites6sp() is a SpatialPointsDataFrame. You can
> get the coordinates by saying:
>
> pointlayer <- getSites6sp("mypoints")
> coords <- coordinates(pointlayer)
>
> and assuming z is called z:
>
> myTSA <- surf.ls(2, x=coords[,1], y=coords[,2], z=pointlayer$z)
>
> but you can also do TSA straight away in gstat:
>
> myTSA_with_gstat <- gstat(id="tr2", formula = z ~ 1, data = pointlayer,
>   degree=2)
>
> (the most recent gstat just takes the location coordinates from the
> SpatialPointsDataFrame object.)
>
> There was a thread about this recently, I think copied to:
>
>
> http://grass.gdf-hannover.de/twiki/pub/GRASS/WebHome/krigingusingRGRASS6.txt
>
> where a grid is created from the GRASS region settings to predict to.
>
> Hope this helps,
>
> Roger
>
> >
> > the whole idea is to make TSA, then variogram fitting in the residuals,
> then
> > krigging (maybe with gstat or geoR, still haven't decided)
> >
> > thanks
> >
> > --
> > +-----------------------------------------------------------+
> >               Carlos Henrique Grohmann - Guano
> >   Geologist M.Sc  - Doctorate Student at IGc-USP - Brazil
> > Linux User #89721  - carlos dot grohmann at gmail dot com
> > +-----------------------------------------------------------+
> > _________________
> > "Good morning, doctors. I have taken the liberty of removing Windows 95
> from
> > my hard drive."
> > --The winning entry in a "What were HAL's first words" contest judged by
> > 2001: A SPACE ODYSSEY creator Arthur C. Clarke
> >
>
> --
> Roger Bivand
> Economic Geography Section, Department of Economics, Norwegian School of
> Economics and Business Administration, Helleveien 30, N-5045 Bergen,
> Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
> e-mail: Roger.Bivand at nhh.no
>
>


--
+-----------------------------------------------------------+
              Carlos Henrique Grohmann - Guano
  Geologist M.Sc  - Doctorate Student at IGc-USP - Brazil
Linux User #89721  - carlos dot grohmann at gmail dot com
+-----------------------------------------------------------+
_________________
"Good morning, doctors. I have taken the liberty of removing Windows 95 from
my hard drive."
--The winning entry in a "What were HAL's first words" contest judged by
2001: A SPACE ODYSSEY creator Arthur C. Clarke
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