Changing the units in a contour plot from vis.gam in mgcv

Question

I'm fitting a model using the log of a variable, and I'd like to present my results in terms of that variable transformed. Here is a simple example:

library(mgcv)
N = seq(from=1,to=10,by=.01)
a = N^2
b = 1/N
y = log(a*b*runif(length(N)))
mod = gam(y~te(a,b))
vis.gam(mod, plot.type="contour")

I'd like to produce the same graph, but based on exp(y) instead of y.

Any ideas how to do this? Thanks in advance.

Answer 1

As often happens, the solution occurred to me immediately after asking the question.

Just type vis.gam and get the function. Copy/paste it into the script file. It is a long function. Somewhere midway:

fv <- predict.gam(x, newdata = newd, se.fit = TRUE, type = type)
fv$fit = exp(fv$fit)   #INSERT THIS LINE HERE WITH WHATEVER FUNCTION YOU WANT TO MODIFY THE FITTED VALUES BY
z <- fv$fit

Then change the function name to "mod.vis.gam" or something, and use it like any function. Works great. Note that SE's aren't affected.