[R] image function with date-time on X axis

[Halldór Björnsson]

I am trying to plot a image where the x axis has the units of time.
When I issue the
image(x,y,z) command with x as a POSIXct object, it fails to put a
time stamp on the
x axis.

Instead I get a warning "Incompatible methods" warning and no dates on
my x axis.

This example shows my problem:

Rmat=t(matrix(data=rnorm(1:500),ncol=10,nrow=50))
tax=seq(ISOdate(2010,4,14,12,0,0), ISOdate(2010,4,19,00,0,0), by = "12
hours") ylevs=seq(100,5000,length=50)
image(tax,ylevs,Rmat)

This givies the warning:
In image.default(tax, zlevs, Rmat) :
  Incompatible methods ("-.POSIXt", "Ops.difftime") for "-"
2: In is.vector(X) :

Contrast the x axis result of image with that of plot
 plot(tax,rnorm(length(tax)))

where the date-time shows stamps work fine.

How can I get image to behave (or is there a better function for the job?)

Sincerely
Halldór