Distance-sampling detection functions and associated density functions

These functions represent the currently available detection functions used for modeling line and point transect data with distsamp. Detection functions begin with "g", and density functions begin with a "d".

gxhn(x, sigma)
gxexp(x, rate)
gxhaz(x, shape, scale)

dxhn(x, sigma)
dxexp(x, rate)
dxhaz(x, shape, scale)
drhn(r, sigma)
drexp(r, rate)
drhaz(r, shape, scale)

Arguments

x

Perpendicular distance

r

Radial distance

sigma

Shape parameter of half-normal detection function

rate

Shape parameter of negative-exponential detection function

shape

Shape parameter of hazard-rate detection function

scale

Scale parameter of hazard-rate detection function

See also

distsamp for example of using these for plotting detection function

Examples

# Detection probabilities at 25m for range of half-normal sigma values.
round(gxhn(25, 10:15), 2)
#> [1] 0.04 0.08 0.11 0.16 0.20 0.25

# Plot negative exponential distributions
plot(function(x) gxexp(x, rate=10), 0, 50, xlab="distance",
    ylab="Detection probability")
plot(function(x) gxexp(x, rate=20), 0, 50, add=TRUE, lty=2)
plot(function(x) gxexp(x, rate=30), 0, 50, add=TRUE, lty=3)


# Plot half-normal probability density functions for line- and point-transects
par(mfrow=c(2, 1))
plot(function(x) dxhn(x, 20), 0, 50, xlab="distance",
    ylab="Probability density", main="Line-transect")
plot(function(x) drhn(x, 20), 0, 50, xlab="distance",
    ylab="Probability density", main="Point-transect")