adehabitat (version 1.8.20)

set.limits: Define the Same Time Limits for several Bursts in a Regular Trajectory

Description

This function sets the same time limits for several bursts in a regular trajectory.

Usage

set.limits(ltraj, begin, dur, pattern,
           units = c("sec", "min", "hour", "day"),
           tz = "", ...)

Arguments

ltraj

an object of class ltraj

begin

a character string which is used to determine the time of beginning of the study period (see below)

dur

the duration of the study period

pattern

a character string indicating the conversion specifications for begin (see below)

units

a character string indicating the time units of dur

tz

A timezone specification to be used for the conversion of begin. System-specific, but "" is the current time zone, and "GMT" is UTC (see help(strptime))

…

additional arguments to be passed to other functions

Value

an object of class ltraj

Details

Some studies are intended to compare regular trajectories of the same duration collected at different period. For example, the aim may be to identify the differences/similarities between different days (each one corresponding to a burst of relocation) in the pattern of movements of an animal between 05H00 and 08H00, with a time lag of 5 minutes. In such cases, it is often convenient that the relocations of the bursts are paired (e.g. the fifth relocation correspond to the position of the animal at 5H30 for all bursts).

The function set.limits is intended to ensure that the time of beginning, the end, and the duration of the trajectory is the same for all bursts of the object ltraj. If relocations are collected outside the limits, they are removed. If the actual time limits of the burst cover a shorter period than those specified, missing values are added.

Note that "time of beginning" is not a synonym for "date". That is, two trajectories of the same animal, both beginning at 05H00 and ending at 08H00, have the same time of beginning, but are necessarily not sampled on the same day, which implies that they correspond to different dates. For this reason, the time of beginning is indicated to the function set.limits by a character string, and the parameter pattern should indicate the conversion specifications. These conversions specifications are widely documented on the help page of the function strptime. For example, to indicate that the trajectory begins at 5H00, the value for begin should be "05:00" and the value for pattern should be "%H:%M". If the trajectory should begin on january 10th, the value for begin should be "01:10" and pattern should be "%m:%d". Note that the only conversion specifications allowed in this function are %S (seconds), %M (minutes), %H (hours), %d (day), %m (month), %Y (year with century), %w (weekday), and %j (yearday). See help(strptime) for additional information on these convention specifications.

See Also

ltraj for additional information on objects of class ltraj, sett0 for additional information on regular trajectories, and sd2df for additionnal information about regular trajectories of the same duration. See also strptime for further information about conversion specifications for dates.

Examples

# NOT RUN {
## load data on the ibex
data(ibex)
ibex

## The monitoring of the 4 ibex should start and end at the same time
## define the time limits

ib2 <- set.limits(ibex, begin="2003-06-01 00:00", dur=14,
                  units="day", pattern="%Y-%m-%d %H:%M")
ib2
is.sd(ib2)

## All the trajectories cover the same study period
## Relocations are collected at the same time. This dataset can now be
## used for studies of interactions between animals

# }