Hello all,
After beating my head against the wall for a few hours, I give up.
I have two problems.
1. If I use seq() to generate a POSIXct series that crosses a daylight savings 
to stardard time change I get two values for the first day of change.  The time 
change is Nov 6,2011.  The value for Nov 7 turns into 23:00 on Nov 6, thus two 
values for Nov 6.  (see below)
So I put a time value (noon) into the sequence, that did give me a correct date 
sequence.

2. When using that modified date sequence in maptools::sunriset(), on day of 
change to stardard time the sunrise time is shifted by one hour. (i.e. Nov5 
8am, Nov6 6am, Nov7 7am)
I can't fathom why sunriset() is giving me funny results on the day of time 
change.  I wonder if there is something amiss with how my windows XP is 
managing time zones perhaps? I would have expected sunriset() to be using just 
the day value from its dateTime argument, not the time component? 
thanks!
Michael

__________________________

 start <- as.POSIXct("2011-11-05")
 end <- as.POSIXct("2011-11-07")
 date.ser<-seq(start,end,by='day')
# time change is Nov 6,2011
 date.ser
#####  Two values for Nov 6 as Nov 7th lost an hour.
[1] "2011-11-05 00:00:00 PDT" "2011-11-06 00:00:00 PDT"
[3] "2011-11-06 23:00:00 PST"


### Add noon to correct flexibility for time shift.
start <- as.POSIXct("2011-11-05 12:00:00")
end <- as.POSIXct("2011-11-07 12:00:00")
date.ser<-seq(start,end,by='day')
date.ser
[1] "2011-11-05 12:00:00 PDT" "2011-11-06 11:00:00 PST"
[3] "2011-11-07 11:00:00 PST"

library(maptools)
 nanaimo <- matrix(c(-123+(-57/60),49+11/60), nrow=1)
 sunriset(nanaimo, date.ser, direction="sunrise", POSIXct.out=T)[,2]
[1] "2011-11-05 08:09:42 PDT" "2011-11-06 06:11:19 PST"
[3] "2011-11-07 07:12:56 PST"

_______________________________________________________
Michael Folkes
Salmon Stock Assessment
Canadian Dept. of Fisheries & Oceans     
Pacific Biological Station
3190 Hammond Bay Rd.
Nanaimo, B.C., Canada
V9T-6N7
Ph (250) 756-7264 Fax (250) 756-7053  michael.fol...@dfo-mpo.gc.ca


        [[alternative HTML version deleted]]

______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

Reply via email to