scripts/vector-averaging.R

In camposfa/paceR: Tools for working with the PACE Database

# Based on function in SDMTools, but fixes problem with incorrect quadrants
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)

      #perform some checks and correct when output in wrong quadrant
      AV <- NULL
      if (Ve >= 0 & Vn >= 0) {
        AV <- AV1
      }
      else if (Ve >= 0 & Vn < 0) {
        AV <- pi - AV1
      }
      else if (Ve < 0 & Vn < 0) {
        AV <- AV1 + pi
      }
      else if (Ve < 0 & Vn >= 0) {
        AV <- 2 * pi - AV1
      }
      else{
        AV <- NULL
      }
      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))
    }
  }
}