#' Helpfunctions for volume: Doublebarkthickness
#'
#' Functions for calculation of doublebark in milimeter
#'
#' @name volumeDoubleBark
#'
#' @param d Diameter in breast hegiht i centimeter including bark
#' @param h Tree height in meter
#' @param sp species codes (1=spruce, 2=pine, 3=Birch)
#' @param Fitje1995 logical indicating to use the functions by Fitje 1995 rather than Brantseg 1967
#' @details bla bla
#' @return b doublebark i mm
#' @author Hans Ole Ørka \email{hans.ole.orka@@gmail.org}
#' @references Braastad, H. 1966. Volume tables for birch. Reports of the Norwegian Forest Research Institute, 21, 265-365.
#' Brantseg, A. 1967. Volume functions and tables for Scots pine. South Norway. Reports of the Norwegian Forest Research Institute, 12, 689-739.
#' Vestjordet, E. 1967. Functions and tables for volume of standing trees. Norway spruce. Reports of the Norwegian Forest Research Institute, 22, 539-574.
#' Fitje A. 1995.
#' @export
volumeDoubleBark <- function(d,h,sp,Fitje1995=FALSE){
# DOBBEL BARK I MM. Gran
Bs <- -0.34 + 0.831648 * d - 0.002832 * d * d - 0.010112 * h * h + 0.700203 * d * d / (h * h)
# DOBBEL BARK I MM. Furu #Brantseg(1967)
Bp <- 2.9571 + 1.1499 * d - 0.7304 * d / h
#Dobbelbark Furu Fitje 1995
if(Fitje1995) {
Bp <- 2.3 + 1.13*d
}
#Dobbelbark Bjørk i mm
Bb <- 1.046 * d
#Dobbelbark i mm
b <- ifelse(sp == 1, Bs, ifelse(sp == 2, Bp, ifelse(sp == 3,Bb,NA)))
return(b)
}
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