[R] date Axes and formats in lattice plots

[Toby.Patterson@csiro.au]

All,

I have some data of animal movements that I'm plotting using xyplot() from lattice. I want to have the date (class POSIXct object) on the Y-axis and the animals longitude on X-axis.
Eg. 

xyplot(date ~ longitude, groups = animal, data = my.data) 

with data like:

     animal   ptt year month day    lon                date
125 03P0014 13273 2003     7  10 150.38 2003-07-10 14:03:48
126 03P0192 20890 2003     7  10 151.13 2003-07-10 14:00:47
127 03P0197 30466 2003     7  10 150.74 2003-07-10 14:02:21
...etc

It all works fine except for the format of the dates that gets displayed. 

I am not sure what I need to change within the lattice frame work to get a specific date format (eg. "%Y-%-m-%d"). Does anyone have any tips or, even better, some example code that they could pass on?

Many thanks. 
Toby