Error when trying to image krig values - r

Question

while trying to Krig benzene values from
WELL.ID X Y BENZENE
1 MW-02 268.8155 282.83 0.00150
2 IW-06 271.6961 377.01 0.00050
3 IW-07 251.0236 300.41 0.01040
4 IW-08 278.9238 300.37 0.03190
5 MW-10 281.4008 414.15 2.04000
6 MW-12 391.3973 449.40 0.01350
7 MW-13 309.5307 335.55 0.01940
8 MW-15 372.8967 370.04 0.01620
9 MW-17 250.0000 428.04 0.01900
10 MW-24 424.4025 295.69 0.00780
11 MW-28 419.3205 250.00 0.00100
12 MW-29 352.9197 277.27 0.00031
13 MW-31 309.3174 370.92 0.17900
i generate a grid (the property these wells reside on) like so
setwd("C:/.....")
getwd()
require(geoR)
require(ggplot2)
a <- read.table("krigbenz_loc.csv", sep = ",", header = TRUE)
b <- data.matrix(a)
c <- as.geodata(b, coords.col = 2:3, data.col = 4, )
ggplot(a, aes(x= X, y= Y, colour="green", label=WELL.ID)) + geom_point() + geom_text(aes(label=WELL.ID),hjust=0, vjust=0)
x.range <- as.integer(range(a[,2]))
y.range <- as.integer(range(a[,3]))
x = seq(from=x.range[1], to=x.range[2], by=1)
y = seq(from=y.range[1], to=y.range[2], by=1)
length(x)
length(y)
xv <- rep(x,length(y))
yv <- rep(y, each=length(x))
in_mat <- as.matrix(cbind(xv, yv))
look at the variogram.. (not very pretty but working on it)
### variogram ###
## on geo-object
v1 <- variog(c)
length(v1$n)
v1.summary <- cbind(c(1:11), v1$v, v1$n)
colnames(v1.summary) <- c("lag", "semi-variance", "# of pairs")
v1.summary
plot(v1, type = "b", main = "Variogram: BENZENE at CRAIG BP")
use ksline to generate krig values...
## variance of benzene readings = sd^2
sd <- sd(a$BENZENE)
var = sd^2
fitted_model <- variofit(vario=v1, ini.cov.pars=c(var, .29), cov.model='exp')
q <- ksline(c, cov.model=fitted_model$cov.model, cov.pars=fitted_model$cov.pars,
nugget=fitted_model$nugget, locations=in_mat)
but then its hold the phones, error when I try to image the results!!!!
> image(q, val = q$predict)
Error in eval(x$call$geodata, envir = attr(x, "parent.env"))$borders :
object of type 'builtin' is not subsettable
this seems to be completely out of left field as I have gone over this several times... I googled the error and it seems that i am trying to call a subset of a function and the answer 90% of the time is that my syntax is wrong somewhere but I have checked everything and I can not figure it out... any help would be greatly appreciated.
thanks
ZR

Answer 1

This looks like a bad evaluation situation in geoR. I mean, a bug!
If you rename your c object to something else, it works:
ccc =c
q <- ksline(ccc, cov.model=fitted_model$cov.model, cov.pars=fitted_model$cov.pars,
nugget=fitted_model$nugget, locations=in_mat)
image(q) # now works
This would be because image.kriging is trying to get something from the original c object, but its not evaluating it in the right context so it gets the R base c function (the word "builtin" in the error was my clue here).
ksline help also says
The function ‘krige.conv’ should be preferred, unless moving
neighborhood is to be used.
so maybe you should try that - it might not have the same problem! Note that it has a different set of arguments to ksline.