R/length_to_breadth.r

In nrcan-cfs-fire/cffdrs: Canadian Forest Fire Danger Rating System

#' Length-to-Breadth ratio
#'
#' @description Computes the Length to Breadth ratio of an elliptically shaped
#' fire. Equations are from listed FCFDG (1992) except for errata 80 from
#' Wotton et. al. (2009).
#'
#' All variables names are laid out in the same manner as Forestry Canada
#' Fire Danger Group (FCFDG) (1992). Development and Structure of the
#' Canadian Forest Fire Behavior Prediction System." Technical Report
#' ST-X-3, Forestry Canada, Ottawa, Ontario.
#'
#' Wotton, B.M., Alexander, M.E., Taylor, S.W. 2009. Updates and revisions to
#' the 1992 Canadian forest fire behavior prediction system. Nat. Resour.
#' Can., Can. For. Serv., Great Lakes For. Cent., Sault Ste. Marie, Ontario,
#' Canada. Information Report GLC-X-10, 45p.
#'
#'  @param FUELTYPE The Fire Behaviour Prediction FuelType
#'  @param WSV The Wind Speed (km/h)
#'
#' @returns Length to Breadth ratio value
#'
#' @noRd

length_to_breadth <- function(FUELTYPE, WSV) {
  # calculation is depending on if fuel type is grass (O1) or other fueltype
  LB <- ifelse(
    FUELTYPE %in% c("O1A", "O1B"),
    # Correction to orginal Equation 80 is made here
    # Eq. 80a / 80b from Wotton 2009
    ifelse(WSV >= 1.0, 1.1 * (WSV**0.464), 1.0), # Eq. 80/81
    1.0 + 8.729 * (1 - exp(-0.030 * WSV))**(2.155)
  ) # Eq. 79
  return(LB)
}

.LBcalc <- function(...) {
  .Deprecated("length_to_breadth")
  return(length_to_breadth(...))
}