bi_di {timbeR}

Estimate the diameter at a given height based on a fitted Bi (2000) taper equation.

Description

Estimates the diameter at a given height of a tree from the diameter at breast height, total height and the coefficients of the Bi taper function.

Usage

bi_di(dbh, h, hi, coef)

Arguments

dbh

tree diameter at breast height, in centimeters.

h

total tree height, in meters.

hi

height at which the diameter will be calculated, in meters.

coef

numerical vector containing seven coefficients of the Bi taper function.

Details

the Bi (2000) variable-form taper function is represented mathematically by the following expression

di ~ dbh * (log(sin((pi/2) * (hi/h)))/(log(sin((pi/2) * (1.3/h)))))^(b0 + b1 * sin((pi/2) * (hi/h)) + b2 * cos((3 * pi/2) * (hi/h)) + b3 * (sin((pi/2) * (hi/h))/(hi/h)) + b4 * dbh + b5 * (hi/h) * dbh^0.5 + b6 * (hi/h) * h^0.5)

Value

a numeric value indicating the diameter at the given height.

Examples

library(dplyr)
library(minpack.lm)
library(timbeR)

tree_scaling <- tree_scaling %>%
mutate(did = di/dbh,
       hih = hi/h)

bi <-  nlsLM(di ~ taper_bi(dbh, h, hih, b0, b1, b2, b3, b4, b5, b6),
data=tree_scaling,
start=list(b0=1.8,b1=-0.2,b2=-0.04,b3=-0.9,b4=-0.0006,b5=0.07,b6=-.14))

coef_bi <- coef(bi)

dbh <- 25
h <- 20
hi <- 15

bi_di(dbh, h, hi, coef_bi)