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#' sun.info estimate the time of sunrise and sunset according to longitude, latitude and date
#' @title Estimate the time of sunrise and sunset according to longitude, latitude and date
#' @author Marc Girondot \email{marc.girondot@@gmail.com}
#' @return A data.frame with information about daily sun
#' @param latitude The latitude at which estimate the sun fates
#' @param longitude The longitude at which estimate the sun fates
#' @param date A vector with the time at which sun fates are needed
#' @family Periodic patterns of indices
#' @description Estimate the sun fates according to latitude and date.\cr
#' Can be compared with the function \code{sunrise.set()} of package \code{StreamMetabolism}.
#' @references Teets, D.A. 2003. Predicting sunrise and sunset times. The College Mathematics Journal 34(4):317-321.
#' @examples
#' \dontrun{
#' # Generate a timeserie of time
#' date <- seq(from=as.Date("2000-01-01"), to=as.Date("2000-12-31"), by="1 day")
#' plot(date, sun.info(date, latitude=23, longitude=0)$day.length, bty="n",
#' las=1, type="l", xlab="Ordinal days", ylab="Day length in hours")
#' plot(date, sun.info(date, latitude=23, longitude=0)$sunrise, bty="n",
#' las=1, type="l", xlab="Ordinal days", ylab="Sun rise in hours")
#' }
#' @export
sun.info <- function(date, latitude, longitude){
d <- as.numeric(as.POSIXlt(date)$yday)+1
Lat <- latitude
Long <- longitude
## d is the day of year
## Lat is latitude in decimal degrees
## Long is longitude in decimal degrees (negative == West)
##This method is copied from:
##Teets, D.A. 2003. Predicting sunrise and sunset times.
## The College Mathematics Journal 34(4):317-321.
## At the default location the estimates of sunrise and sunset are within
## seven minutes of the correct times (http://aa.usno.navy.mil/data/docs/RS_OneYear.php)
## with a mean of 2.4 minutes error.
## Function to convert degrees to radians
rad <- function(x) pi*x/180
##Radius of the earth (km)
R=6378
##Radians between the xy-plane and the ecliptic plane
epsilon=rad(23.45)
##Convert observer's latitude to radians
L=rad(Lat)
## Calculate offset of sunrise based on longitude (min)
## If Long is negative, then the mod represents degrees West of
## a standard time meridian, so timing of sunrise and sunset should
## be made later.
timezone = -4*(abs(Long)%%15)*sign(Long)
## The earth's mean distance from the sun (km)
r = 149598000
theta = 2*pi/365.25*(d-80)
z.s = r*sin(theta)*sin(epsilon)
r.p = sqrt(r^2-z.s^2)
t0 = 1440/(2*pi)*acos((R-z.s*sin(L))/(r.p*cos(L)))
##a kludge adjustment for the radius of the sun
that = t0+5
## Adjust "noon" for the fact that the earth's orbit is not circular:
n = 720-10*sin(4*pi*(d-80)/365.25)+8*sin(2*pi*d/365.25)
## now sunrise and sunset are:
sunrise = (n-that+timezone)/60
sunset = (n+that+timezone)/60
UTC <- (((7.5+Long)%%360)) %/% 15
if (UTC>12) {UTC <- 12-UTC;tz <- "Etc/GMT"} else {tz <- "Etc/GMT+"}
tz <- paste0(tz, UTC)
df <- data.frame(sunrise = sunrise, sunset = sunset, day.length=sunset- sunrise,
date.time.sunrise=as.POSIXlt(format(date, "%Y-%m-%d"), tz=tz)+sunrise*60*60,
date.time.sunset=as.POSIXlt(format(date, "%Y-%m-%d"), tz=tz)+sunset*60*60)
sunrise.UTC <- as.POSIXlt(format(df$date.time.sunrise, format="%Y-%m-%d %H:%M:%S"),
tz="UTC", use.tz=TRUE)
sunrise.UTC.dec <- sunrise.UTC$hour + sunrise.UTC$min/60 + sunrise.UTC$sec/3600
sunset.UTC <- as.POSIXlt(format(df$date.time.sunset, format="%Y-%m-%d %H:%M:%S"),
tz="UTC", use.tz=TRUE)
sunset.UTC.dec <- sunset.UTC$hour + sunset.UTC$min/60 + sunset.UTC$sec/3600
df <- cbind(df, date.time.sunrise.UTC=sunrise.UTC, date.time.sunset.UTC=sunset.UTC,
time.sunrise.UTC=sunrise.UTC.dec, time.sunset.UTC=sunset.UTC.dec)
return(df)
}
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