#' Circular Averaging based on Vector Averaging
#'
#' \code{circular.averaging} calculates the average direction (0 - 360) given a
#' vector of directions.\cr\cr \code{vector.averaging} calculates the average
#' distance and direction given a vector of directions and a vector of
#' distances.
#'
#' functions return `NA` if the average distance or direction is not valid...
#' \emph{e.g.}, when averaging directions of 0 & 180 degrees, the result could
#' theoretically be 90 or 270 but is practically neither.
#'
#' @note
#' This function was taken from the now archived, as of 08/03/2020,
#' \pkg{SDMtools}.
#'
#' @param direction a vector of directions given in degrees (0 - 360) if
#' `deg == TRUE` or in radians if `deg == FALSE`
#' @param distance a vector of distances associated with each direction
#' @param deg a boolean object defining if `direction` is in degrees
#' (`TRUE`) or radians (`FALSE`)
#' @return \code{circular.averaging} returns the average direction while
#' \code{vector.averaging} returns a list with 2 elements distance & direction
#' @author Jeremy VanDerWal \email{jjvanderwal@@gmail.com} & Lorena Falconi
#' \email{lorefalconi@@gmail.com}
#' @examples
#'
#' #EXAMPLE circular.averaging
#' circular.averaging(c(0,90,180,270)) #result is NA
#' circular.averaging(c(70,82,96,110,119,259))
#'
#' #EXAMPLE vector.averaging
#' vector.averaging(c(10,20,70,78,108), distance=10)
#' vector.averaging(c(159,220,258,273,310),distance=runif(5))
#'
#' @export
circular.averaging <- function(direction, deg = TRUE) {
n = length(direction) #get the length of direction vector
out = vector.averaging(direction = direction,
distance = rep(1, n),
deg = deg)
return(out$direction)
}
#' @rdname circular.averaging
#' @export
vector.averaging = function(direction, distance, deg = TRUE) {
if (deg)
direction = direction * pi / 180 #convert to radians
n = length(direction) #get the length of direction vector
if (any(is.na(direction))) {
#ensure no NA data
warning('NAs in data')
pos = which(is.na(direction))
direction = direction[-pos]
distance = distance[-pos]
} else {
sinr <- sum(sin(direction))
cosr <- sum(cos(direction))
if (sqrt((sinr ^ 2 + cosr ^ 2)) / n > .Machine$double.eps) {
Ve = sum(distance * sin(direction)) / n
Vn = sum(distance * cos(direction)) / n
UV = sqrt(Ve ^ 2 + Vn ^ 2)
AV1 = atan(Ve / Vn)
AV2 = atan2(sinr, cosr)
#perform some checks and correct when output in wrong quadrant
AV = NULL
if (abs(AV1 - AV2) <= .Machine$double.eps) {
#if both methods of determining directions are reporting the same values
if (AV1 > 0)
AV = AV1
if (AV1 < 0)
AV = 2 * pi + AV1
} else {
#case when they are different values... add necessary values of pi
if (AV1 > 0)
AV = AV1 + pi
if (AV1 < 0)
AV = AV2
}
if (is.null(AV)) {
return(list(distance = NA, direction = NA))
} else {
if (deg)
AV = AV * 180 / pi #convert back to degrees
return(list(distance = UV, direction = AV))
}
} else {
return(list(distance = NA, direction = NA))
}
}
}
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