[R] still have problem with krige and border option
Lionel
l.bargeot at educagri.fr
Tue Apr 16 18:08:04 CEST 2002
Dear all,
I would like to estimate rainfall with the krige function. First, I produce a
polygon of my region of interest (where poly_test.txt is a x,y suite of
points defining a polygon, obtained with the grass v.out.ascii command) :
user>border_limite<-read.table("/home/lionel/rwork/poly_test.txt",header=FALSE)
user>polygone<-list(x=border_limite[,1],y=border_limite[,2])
So now I have a list of x,y coordinates to limit my work area.
If I call the function krige with extrap=FALSE like this
user>grid2.krige<-krige(grid2.point,logtab.point,'lz',
logtab.Exp,maxdist=NULL,extrap=FALSE)
[ where grid2.point is a point object to store prediction, logtab.point a
point object containing points data, 'lz' is the variable name in
logtab.point, logtab.Exp is a variogram object ]
all works quiet well, but I am limited to a convex hull inside the limite
designed by points of measure.
If I set extrap=TRUE, all works, but values are estimated all over my area.
Now if use the polygon I defined, and specifie it in the function call
user>grid2.krige<-krige(grid2.point,logtab.point,'lz',
logtab.Exp,maxdist=NULL,extrap=TRUE,border=polygone)
all points in the area are estimated.
I've tried to put extrap=FALSE with border, but then there is no result, and
no points are found.
Here is my polygon definition:
$x
[1] 2272048 2275274 2296044 2293826 2280517 2272048
$y
[1] 781270.4 801031.7 795385.6 773003.0 765945.4 781270.4
So my question is, do you see any stupid mistake I can make ?
last point (optional!) about krige.G
I also tried to use krige.G from the grass package, but for the moment I have
a strange error message : (where G is obtained with gmeta() command)
user>grid2.krige<-krige.G(logtab.point,"lz",logtab.Exp,G)
Error in surf.gls(0, expcov, x = point.obj$x, y = point.obj$y, z = at.val, :
Rank failure in Choleski decomposition
I've just reported my point and variogram definition in the options. Perhap's
is there a small difference between parameters when they are passed to krige
function but I don't see wich.
Thanks in advance for all kind of help
Lionel
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