R/getWeights.R

In environmentalinformatics-marburg/Reot: Empirical Orthogonal Teleconnections in R

#' Calculate weights from latitude
#' 
#' Calculate weights using the cosine of latitude to compensate for area 
#' distortion of non-projected lat/lon data
#' 
#' @param x a Raster* object
#' @return a numeric vector of weights
#' @examples 
#' data("australiaGPCP")
#' wghts <- getWeights(australiaGPCP)
#' wghts.rst <- australiaGPCP[[1]]
#' wghts.rst[] <- wghts
#' 
#' opar <- par(mfrow = c(1,2))
#' plot(australiaGPCP[[1]], main = "data")
#' plot(wghts.rst, main = "weights")
#' par(opar)
#' 
#' @export getWeights
getWeights <- function(x) {
  cos(deg2rad(coordinates(x)[, 2][!is.na(x[[1]][])]))
}