adehabitat (version 1.1-1)

angles: Compute Turning Angles

Description

angles computes the turning angles (in radians) between consecutive moves from an object of class traj. See examples for a clearer definition.

Usage

angles(x, id = levels(x$id), burst = levels(x$burst), date = NULL)

Arguments

x

an object of class traj

id

a character vector giving the identity of the animals for which the angles are to be computed

burst

a character vector giving the identity of the circuits for which the angles are to be computed (see as.traj)

date

a vector of class POSIXct of length 2 (beginning, end) delimiting the period of interest

Value

• Returns a data frame with the following components:
• id
  the identity of the animal
• x
  the x coordinate of the relocation at which the angle is computed
• y
  the y coordinate of the relocation at which the angle is computed
• date
  a vector of class POSIXct, giving the date at which the relocation has been taken
• burst
  the id of the circuit (see help(as.traj))
• angles
  the turning angles between the successive moves.

References

Turchin, P. (1998) Quantitative analysis of movement. Measuring and modeling population redistribution in animals and plants. Sunderland, Massachusetts: Sinauer Associates.

See Also

speed for computation of movement speeds, as.traj for additional information about objects of class traj

Examples

## loads an object of class "traj"
data(puechcirc)
puechcirc

## Gets a part of the trajectory of the wild boar named
## CH93 and draws it
## Also displays the turning angles
toto <- puechcirc[2:5,]
plot(toto$x, toto$y, asp = 1, ylim = c(3158300, 3158550),
     pch = 16,
     main = "Turning angles between
three consecutive moves",
     xlab="X", ylab="Y")
lines(toto$x, toto$y)
lines(c(toto$x[2], 700217.6),
      c(toto$y[2], 3158310), lty=2)
lines(c(toto$x[3],700289),
      c(toto$y[3],3158546), lty=2)
ang1x <- c(700234.8, 700231.9, 700231, 700233.7, 700238.8, 700243.2)
ang1y <- c(3158332, 3158336, 3158341, 3158347, 3158350, 3158350)
ang2x <- c(700283.3, 700278.8, 700275.4, 700272.4, 700271.2, 700271.6,
           700274.7)
ang2y <- c(3158522, 3158522, 3158520, 3158517, 3158514, 3158508, 3158504)
lines(ang1x, ang1y)
lines(ang2x, ang2y)
text(700216.1, 3158349, expression(theta[1]), cex=2)
text(700247.7, 3158531, expression(theta[2]), cex=2)
text(c(700301, 700231), c(3158399, 3158487),
     c("Beginning", "End"), pos=4)



## Computation of the turning angles with real data
## on wild boars
plot(puechcirc)
ang <- angles(puechcirc)

## The angles are in the column Angles:
ang[1:4,]