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")