R/distance_at_time.r

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

#' Distance at time t calculator
#'
#' @description Calculate the Head fire spread distance at time t. In the
#' documentation this variable is just "D".
#'
#' 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.
#'
#' @param FUELTYPE The Fire Behaviour Prediction FuelType
#' @param ROSeq    The predicted equilibrium rate of spread (m/min)
#' @param HR       The elapsed time (min)
#' @param CFB      Crown Fraction Burned
#'
#' @return DISTt - Head fire spread distance at time t
#' @noRd

distance_at_time <- function(FUELTYPE, ROSeq, HR, CFB) {
  # Eq. 72 (FCFDG 1992)
  # Calculate the alpha constant for the DISTt calculation
  alpha <- ifelse(
    FUELTYPE %in% c("C1", "O1A", "O1B", "S1", "S2", "S3", "D1"),
    0.115,
    0.115 - 18.8 * (CFB**2.5) * exp(-8 * CFB)
  )
  # Eq. 71 (FCFDG 1992) Calculate Head fire spread distance
  DISTt <- ROSeq * (HR + exp(-alpha * HR) / alpha - 1 / alpha)
  return(DISTt)
}

.DISTtcalc <- function(...) {
  .Deprecated("distance_at_time")
  return(distance_at_time(...))
}