TrajSpeedIntervals: Calculate speed time intervals

In JimMcL/trajr: Animal Trajectory Analysis

Calculate speed time intervals

Description

Calculates and returns a list of time intervals during which speed is slower and/or faster than specified values. Speed is calculated by taking the modulus of velocity (TrajVelocity).

Usage

TrajSpeedIntervals(
  trj,
  fasterThan = NULL,
  slowerThan = NULL,
  interpolateTimes = TRUE,
  diff = c("backward", "central", "forward")
)

Arguments

trj	Trajectory to be analysed.
fasterThan, slowerThan	If not NULL, intervals will cover time periods where speed exceeds/is lower than this value. At least one of fasterThan, or slowerThan must be specified.
interpolateTimes	If TRUE, times will be linearly interpolated between frames.
diff	Method used to calculate speed, see TrajVelocity for details. The default is "backward" to maintain backwards compatibility; in general, "central" provides a more accurate estimate of velocity.

Value

A data frame of class "TrajSpeedIntervals", each row is an interval, columns are:

startFrame	Indices of frames at the start of each interval.
stopFrame	Indices of frames at the end of each interval.
startTime	Time since start of trajectory at the start of each interval.
stopTime	Time since start of trajectory at the end of each interval
duration	Duration of each interval.

The data frame will also have non-standard attributes:

trajectory	Value of the trj argument.
slowerThan	Value of the slowerThan argument.
fasterThan	Value of the fasterThan argument.
speed	Data frame with columns speed and time.
derivs	Value returned by calling TrajDerivatives(trj). Provided for backwards-compatibility; use of the speed attribute is now preferred to the derivs attribute.

See Also

TrajVelocity for calculating trajectory velocity, plot.TrajSpeedIntervals for plotting speed over time with intervals highlighted.

Examples

# Plot speed, highlighting intervals where speed drops below 50 units/sec
set.seed(4)
trj <- TrajGenerate(200, random = TRUE)
smoothed <- TrajSmoothSG(trj, 3, 101)
intervals <- TrajSpeedIntervals(smoothed, diff = "central", slowerThan = 50, fasterThan = NULL)
plot(intervals)

# Report the duration of the longest period of low speed
cat(sprintf("Duration of the longest low-speed interval was %g secs\n", max(intervals$duration)))

JimMcL/trajr documentation built on July 23, 2024, 2:06 a.m.