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# Author: Robert J. Hijmans
# License GPL3
if (!isGeneric("photoperiod")) {setGeneric("photoperiod", function(x, ...) standardGeneric("photoperiod"))}
setMethod("photoperiod", signature(x="Date"),
function(x, latitude) {
x <- fromDate(x, "doy")
x <- cbind(x, latitude)
.Call('_meteor_Photoperiod', PACKAGE = 'meteor', x[,1], x[,2])
}
)
setMethod("photoperiod", signature(x="numeric"),
function(x, latitude) {
x <- cbind(x, latitude)
.Call('_meteor_Photoperiod', PACKAGE = 'meteor', x[,1], x[,2])
}
)
setMethod("photoperiod", signature(x="data.frame"),
function(x) {
if (!all(c("date", "latitude") %in% names(x))) {
stop("x must have variables 'date', and 'latitude'")
}
doy <- fromDate(x$date, "doy")
.Call('_meteor_Photoperiod', PACKAGE = 'meteor', x$date, x$latitude)
}
)
setMethod("photoperiod", signature(x="SpatRaster"),
function(x, filename="", overwrite=FALSE, ...) {
d <- terra::time(x)
if (all(is.na(d))) {
stop("the layers in x have no time stamps")
}
r <- terra::rast(x)
if (!terra::is.lonlat(x)) {
lat <- terra::as.points(r, values=FALSE, na.rm=FALSE)
lat <- terra::project(lat, crs="+proj=longlat")
lat <- terra::crds(lat)[,2]
dd <- data.frame(latitude=rep(lat, length(d)), date=rep(d, each=length(lat)))
r <- terra::rast(x)
terra::values(r) <- photoperiod(dd)
if (filename != "") {
r <- terra::writeRaster(r, filename=filename, overwrite=overwrite, ...)
}
r
} else {
r <- r[,1,drop=FALSE]
terra::ext(r) <- terra::ext(x)
lat <- terra::yFromRow(r, 1:nrow(r))
dd <- data.frame(latitude=rep(lat, length(d)), date=rep(d, each=length(lat)))
terra::values(r) <- photoperiod(dd)
terra::disagg(r, c(1, ncol(x)), filename=filename, overwrite=overwrite, ...)
}
}
)
.daylength <- function(lat, doy) {
if (inherits(doy, 'Date') | inherits(doy, 'character')) {
doy <- fromDate(doy, "doy")
}
lat[lat > 90 | lat < -90] <- NA
doy <- doy %% 365
#Ecological Modeling_, volume 80 (1995) pp. 87-95, called "A Model
#Comparison for Daylength as a Function of Latitude and Day of the Year."
P <- asin(0.39795 * cos(0.2163108 + 2 * atan(0.9671396 * tan(0.00860*(doy-186)))))
a <- (sin(0.8333 * pi/180) + sin(lat * pi/180) * sin(P)) / (cos(lat * pi/180) * cos(P));
a <- pmin(pmax(a, -1), 1)
DL <- 24 - (24/pi) * acos(a)
return(DL)
}
.daylength2 <- function(lat, doy) {
if (inherits(doy, 'Date') | inherits(doy, 'character')) {
doy <- doyFromDate(doy)
}
lat[lat > 90 | lat < -90] <- NA
doy <- doy %% 365
# after Goudriaan and Van Laar
RAD <- pi/180
# Sine and cosine of latitude (LAT)
SINLAT <- sin(RAD * lat);
COSLAT <- cos(RAD * lat);
# Maximal sine of declination;}
SINDCM <- sin(RAD * 23.45)
#{Sine and cosine of declination (Eqns 3.4, 3.5);}
SINDEC <- -SINDCM * cos(2*pi*(doy+10)/365)
COSDEC <- sqrt(1-SINDEC*SINDEC);
#The terms A and B according to Eqn 3.3;}
A <- SINLAT*SINDEC;
B <- COSLAT*COSDEC;
C <- A/B;
#Daylength according to Eqn 3.6; arcsin(c) = arctan(c/sqrt(c*c+1))}
DAYL <- 12* (1+(2/pi)* atan(C/sqrt(C*C+1)))
return(DAYL)
}
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