Error when trying to image krig values

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.