R/daylength.R

In pheno: Auxiliary Functions for Phenological Data Analysis

# calculates daylength dl [h] and declination delta  [radians]
# on day i for latitude lat [degrees]
# declination: angle between sun rays and equatorial plane for 
# the whole earth (-23 degrees - + 23 degrees)
daylength <- function(i,l) {
	if(!is.integer(i)) stop("daylength: first argument must be an integer. Exiting ...")	
	res <- .C("Cdaylength",l=as.double(l),i=as.integer(i),dl=double(1),delta=double(1))
	
	return(list(dl=res$dl, delata=res$delta))

}