Re: [R] maptools sunrise sunset function

From: Farley, Robert <FarleyR_at_metro.net>
Date: Mon, 10 Nov 2008 11:20:03 -0800

I have a time zone problem.

Running the code provided I get the result in UTC, and a lot of warnings like this:
28: In as.POSIXlt.POSIXct(x, tz) ... : unknwon timezone 'PST'

> sunrise.set(34.11583, -118.18719, "2008-11-14")

                   sunrise              sunset
newlon 2008-11-14 14:25:02 2008-11-15 00:49:09
>
> Sys.timezone()

[1] "PST"
>

The result is equivalent to 06:25:02 16:49:09 {PST = UTC-8} The "correct" values from another source show 06:25 16:50 which agree to beyond the accuracy of prediction due to atmospheric uncertainty.

How SHOULD I specify the TZ? I would think that PST is a pretty "standard" ;-) time zone.

Yes, I steal a lot of code snippets. I justify it by telling myself it helps me learn R.  

Robert Farley
Metro
www.Metro.net  

-----Original Message-----
From: r-help-bounces_at_r-project.org [mailto:r-help-bounces_at_r-project.org] On Behalf Of stephen sefick
Sent: Saturday, November 08, 2008 17:09
To: R-help
Subject: Re: [R] maptools sunrise sunset function

Nevermind, when one puts in the proper coordinates in decimal degrees everything works just fine.
thanks for you patience,

Stephen

On Sat, Nov 8, 2008 at 7:40 PM, stephen sefick <ssefick_at_gmail.com> wrote:
> ##This is a function that I am trying to write to calculate sunrise
> and sunset and works "mostly", but returns nonsensical values. What
> am I #missing? Thanks in advance.
>
> ###remember to include maptools as dependence###
> library(maptools)
> sunrise.set <- function(lat, long, date, timezone="UTC", num.days=1){
> #this needs to be long lat#
> lat.long <- matrix(c(long, lat), nrow=1)
> day <- as.POSIXct(date, tz=timezone)
> sequence <- seq(from=day, length.out=num.days , by="days")
> sunrise <- sunriset(lat.long, sequence, direction="sunrise",
POSIXct=TRUE)
> sunset <- sunriset(lat.long, sequence, direction="sunset",
POSIXct=TRUE)
> ss <- data.frame(sunrise, sunset)
> ss <- ss[,-c(1,3)]
> colnames(ss)<-c("sunrise", "sunset")
> return(ss)
> }
>
> #This doesn't make any sense
> sunrise.set(33.46, 84.25, "2008-11-08", timezone="EST")
>
>
> --
> Stephen Sefick
> Research Scientist
> Southeastern Natural Sciences Academy
>
> Let's not spend our time and resources thinking about things that are
> so little or so large that all they really do for us is puff us up and
> make us feel like gods. We are mammals, and have not exhausted the
> annoying little problems of being mammals.
>
> -K.
Mullis
>

-- 
Stephen Sefick
Research Scientist
Southeastern Natural Sciences Academy

Let's not spend our time and resources thinking about things that are
so little or so large that all they really do for us is puff us up and
make us feel like gods.  We are mammals, and have not exhausted the
annoying little problems of being mammals.

								-K.
Mullis

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Received on Mon 10 Nov 2008 - 19:28:39 GMT

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