[GRASSLIST:10737] krigging result looks weird

[Carlos "Guâno" Grohmann]

Hello again

I was playing with R, I get a SRTM (90m) raster, converted it to
vector, put it into R, calculate variogram and krigged a new map, with
30m resolution. The final maps looks "pixelate" (see attach)... Maybe
the parameters I used?

here's what I did:

1-r.to.vect (90m)
2-g.region res=30

R:

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);

library(gstat);

variog1 <- variogram(resid.trend$resid1 ~ 1, locations=resid.trend,
width=90, cutoff=1200);
plot(variog1);

vrg.eye<-(vgm(psill=7500, model="Gau", range=420, nugget=0));
plot(variog1, model=vrg.eye);

vrg.fit<-fit.variogram(variog1,vrg.eye);
vrg.fit;

  model     psill    range
1   Nug  173.7465   0.0000
2   Gau 7661.1776 442.5015

plot(variog1, model=vrg.fit);
vrg.eye2<-(vgm(psill=7650, model="Gau", range=440, nugget=170));
plot(variog1, model=vrg.eye2);

OK_pred <- krige(srtm$cat ~ 1, loc=srtm, newdata=mask_SG,
model=vrg.eye2, maxdist=270);
names(OK_pred);
writeRast6sp(OK_pred, "srtm.krig", zcol="var1.pred", NODATA=-9999);


thanks again

--
+-----------------------------------------------------------+
              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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