Getting tick positions

Thanks for the answers - I should have been more specific as I had already 
tried axTicks and pretty.

The function in question is gantt.chart() in the latest plotrix package 
(Thanks to Scott Waichler for the original code). I settled on axis.POSIXct 
as it seemed the most appropriate for this function, but couldn't find a way 
to get the positions of the ticks so that I could then draw grid lines along 
the months|days|hours. While the trick of copying the original function 
works, I wondered why the axis* functions don't return the tick positions as 
barplot returns the bar positions. Is there any reason not to return "z", or 
is it just historical?

Jim