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#' Calculates the area of a given region.
#'
#' Calculates the area of a given region to a given precision.
#'
#'
#' @param data The region, should contain \$lat and \$lon.
#' @param ngrdpts The precision of the calculation.
#' @param Projection Which projection is beeing used.
#' @param old.method If true an older version of this program is used. Default
#' is False.
#' @param robust If true a more robust method is used, default is True.
#' @return The area of the region given.
#' @section Side Effects: None
#' @seealso \code{\link{geodefine}}, \code{\link{geolocator}},
#' \code{\link{geoinside}}.
#' @examples
#'
#' geoarea(island) # Calculates the area of Iceland up to
#' # an with default precision.
#'
#' geoarea(island,10000) # Calculates the area of Iceland up to
#' # an adiquite precision.
#'
#' # geoarea(geodefine(),10) # Calculates the area of a region specified
#' # by the user.
#'
#' @export geoarea
geoarea <-
function(data, Projection = "Lambert", old.method = F, ngrdpts = 2000, robust
= T)
{
area <- 0
data <- geo.Split.poly(data)
if(old.method) {
for(i in 1:length(data))
area <- area + geoarea.old(data[[i]], ngrdpts, robust)
}
else {
area <- 0
for(i in 1:length(data)) {
if(Projection == "Lambert")
data[[i]] <- lambert(data[[i]]$lat, data[[i]]$
lon, mean(data[[i]]$lat), mean(data[[
i]]$lon), mean(data[[i]]$lat))
else data[[i]] <- mercator(data[[i]]$lat, data[[i]]$
lon, b0 = mean(data[[i]]$lat))
data[[i]] <- data.frame(x = data[[i]]$x, y = data[[
i]]$y)
n <- nrow(data[[i]])
area <- area + abs(sum(data[[i]]$x[1:(n - 1)] * data[[
i]]$y[2:n] - data[[i]]$x[2:n] * data[[i]]$
y[1:(n - 1)], na.rm = T)/2)
}
}
return(area)
}
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