[R] POSIX, time zone and Windows

[Patrick Giraudoux]

Dear Listers,

Apologize to pile up on the 'tz' issue in POSIX objects. I have a 
'simple' thing on which I must make up my mind but cannot do it from the 
existing R-help threads. I am currently working on dog telemetry in 
China, and download time information from GPS collars. I would like to 
set up the corresponding POSIXxx variables in R to a given time zone. Eg 
Pekin GMT+8:00.

I cannot find out how to do it properly. For instance:

mydate<-""06/05/16/11:30:00""
mydate<-strptime(mydate, "%y/%m/%d/%H:%M:%S")

mydate
[1] "2006-05-16 11:30:00"
as.POSIXct(mydate)
[1] "2006-05-16 11:30:00 Paris, Madrid"

Which is obviously not what I wish regarding the specification Paris, 
Madrid...

I have tried to pass something to the argument tz

mydate2<-strptime(mydate, "%y/%m/%d/%H:%M:%S",tz="GMT") or
mydate2<-strptime(mydate, "%y/%m/%d/%H:%M:%S",tz="GMT+08")

I get this:

mydate2
[1] NA

Is there a way to specify the time zone on which I was working (actually 
GTM + 8:00)? I have read in R-help that this is system dependent, but 
the how to do it still escape. Working with Windows, I have checked the 
following address given by Gabor Grothendieck in R-help, 
http://msdn2.microsoft.com/en-us/library/90s5c885.aspx, but I cannot 
manage with the syntax: *TZ*=tzn[+ | –]hh[*:*mm[*:*ss] ][dzn]. They 
mention a three lettre time zone (where can the corresponding codes be 
found?) to which to add a difference in hours between UTC and the local 
time... but any trial I did specifying tz="UTM+08" or other combination 
leads nowhere...

Thanks for any hint...

Patrick