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@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@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