# Kriging Carry out spatial prediction (or kriging). ```r krige(s, point.obj, at, var.mod.obj, maxdist=NULL, extrap=FALSE, border) ``` ## Arguments - `s`: a point object, generated by `point()`, at which prediction is carried out - `point.obj`: a point object, generated by `point()`, containing the sample points and data - `at`: the variable, contained in `point.obj`, for which prediction will be carried out - `var.mod.obj`: variogram object - `maxdist`: an optional maximum distance. If entered, then only sample points (i.e, in point.obj) within maxdist of each prediction point will be used to do the prediction at that point. If not entered, then all n sample points will be used to make the prediction at each point. - `extrap`: logical, indicates if prediction outside the convex hull of data points should be done, default `FALSE` - `border`: optional polygon (list with two components `x` and `y` of same length) representing a (possibly non convex) region of interest to be used instead of the convex hull. Needs `extrap=TRUE`. ## Returns A point object which is a copy of the `s` object with two new variables, `zhat` and `sigma2hat`, which are, repspectively, the predicted value and the kriging variance. ## See Also `est.variogram`,`fit.variogram` ## Examples ```r # a single point: prdpnt <- point(data.frame(list(x=180000,y=331000))) prdpnt <- krige(prdpnt, maas.point, 'zinc', maas.vmod) prdpnt # kriging on a grid (slow!) grid <- list(x=seq(min(maas$x),max(maas$x),by=100), y=seq(min(maas$y),max(maas$y),by=100)) grid$xr <- range(grid$x) grid$xs <- grid$xr[2] - grid$xr[1] grid$yr <- range(grid$y) grid$ys <- grid$yr[2] - grid$yr[1] grid$max <- max(grid$xs, grid$ys) grid$xy <- data.frame(cbind(c(matrix(grid$x, length(grid$x), length(grid$y))), c(matrix(grid$y, length(grid$x), length(grid$y), byrow=TRUE)))) colnames(grid$xy) <- c("x", "y") grid$point <- point(grid$xy) data(maas.bank) grid$krige <- krige(grid$point,maas.point,'zinc',maas.vmod, maxdist=1000,extrap=FALSE,border=maas.bank) op <- par(no.readonly = TRUE) par(pty="s") plot(grid$xy, type="n", xlim=c(grid$xr[1], grid$xr[1]+grid$max), ylim=c(grid$yr[1], grid$yr[1]+grid$max)) image(grid$x,grid$y, matrix(grid$krige$zhat,length(grid$x),length(grid$y)), add=TRUE) contour(grid$x,grid$y, matrix(grid$krige$zhat,length(grid$x),length(grid$y)), add=TRUE) data(maas.bank) lines(maas.bank$x,maas.bank$y,col="blue") par(op) ``` ## References http://www.gis.iastate.edu/SGeoStat/homepage.html

krige function