calc_area: Area of a Cross Section

In mkoohafkan/RAStestR: Functions for testing RAS outputs

Description

Compute cross section area from station-elevation data. This function is used internally by xs_area and should not be called by the user directly.

Usage

calc_area(dist, elev, left.bank = NA, right.bank = NA,
  reference.elev = NA, bottom.elev = NA)

Arguments

dist	The lateral cross section stations.
elev	The cross section elevations at each station.
left.bank	The left bank station. If NA, the minimum distance will be used.
right.bank	The right bank station. If NA, the minimum distance will be used.
reference.elev	The reference elevation to use for computing volume. Note that specifying a reference elevation lower than the maximum elevation of the cross section can introduce some error in the volume computation if the cross section data is not dense. If NA, the maximum elevation of the cross section will be used.
bottom.elev	Minimum elevation below which to ignore cross section volume; effectively flattens the cross section. Note that specifying a bottom elevation higher than the minimum elevation of the cross section can introduce some error in the volume computation if the cross section data is not dense. If NA, the minimum elevation of the cross section will be used.

Value

The flow area of the cross section. The maximum elevation is used as the upper boundary.

Examples

test = data.frame(
  Distance = c(100, 120, 130, 150, 160, 180, 190, 210, 220, 240),
  Elevation = c(100, 100, 80, 80, 60, 60, 80, 80, 100, 100)
)
test.dens = data.frame(
  Distance = approx(test$Distance, test$Distance, xout = seq(100, 240))$y,
  Elevation = approx(test$Distance, test$Elevation, xout = seq(100, 240))$y
)
trap_area = function(a,b,h) 0.5*(a + b)*h
RAStestR:::calc_area(test$Distance, test$Elevation)
trap_area(100, 80, 20) + trap_area(40, 20, 20)
RAStestR:::calc_area(test.dens$Distance, test.dens$Elevation)
trap_area(100, 80, 20) + trap_area(40, 20, 20)
RAStestR:::calc_area(test$Distance, test$Elevation,
  left.bank = 160, right.bank = 180)
RAStestR:::calc_area(test.dens$Distance, test.dens$Elevation,
  left.bank = 160, right.bank = 180)
trap_area(20, 20, 40)
RAStestR:::calc_area(test.dens$Distance, test.dens$Elevation, right.bank = 150)
trap_area(30, 20, 20)
RAStestR:::calc_area(test.dens$Distance, test.dens$Elevation, left.bank = 210)
trap_area(10, 0, 20)
RAStestR:::calc_area(test.dens$Distance, test.dens$Elevation, bottom.elev = 80)
trap_area(100, 80, 20)
RAStestR:::calc_area(test.dens$Distance, test.dens$Elevation, reference.elev = 80)
trap_area(40, 20, 20)

mkoohafkan/RAStestR documentation built on July 14, 2019, 11:41 p.m.