rwalcSimulate: RWalc track sampler

In SWotherspoon/RWalc: Continuous-Time Correlated Random Walk Models for Animal Movement

Description

Simulate a new track from the parameters of a fitted rwalc model.

Usage

rwalcSimulate(
  data,
  par,
  fixed = NULL,
  fixed.err = diag(1e-06, 4, 4),
  point.check = function(tm, x, y) TRUE,
  point.accept = NULL
)

Arguments

data	A dataframe representing the template track.
par	The model parameters.
fixed	An integer vector indicating which locations in the template path are to be held fixed.
fixed.err	Covariance matrix for fixed points.
point.check	A function that accepts a time, and an x,y location and returns a logical indicating whether the location is acceptable.
point.accept	A logical vector indicating which locations should not be checked with the point.check function. Defaults to the value of fixed.

Details

Given a template track and the parameters of a rwalc model this function generates a new track of the same length that coincides with the fitted track at the start point and optionally other specified points along the template track.

Locations from the template track can be marked as fixed with the fixed argument. This should either be NULL or a vector with an entry for each location, with entries indicating

• 0 the location is not fixed

• 1 the location is fixed

• 2 the location is fixed and the point may be a cusp (autocorrelation is reset).

In the current implementation the first location in each segment must be fixed. The fixed.err parameter specifies the covariance of the error in the fixed points, allowing the user to control how acccurately the simulated track reproduces the four components (locations and velocities) of the fixed points.

Additional constraints can be placed on the path by rejection sampling through the function point.check. This function must accept a time, x and y and return a logical indicating whether the point is acceptable. For example, the track can be constrained to the ocean by supplying a point.check function that compares the state to a land mask and returns FALSE for locations on land.

The point.accept can be used to mark points that should not be checked in the rejection step. Currently this defaults to the value of fixed - so by default fixed points are never checked.

Tracks are simulated in the plane. There is is no polar correction and without a suitable point.check function, there is nothing prevent the track extending outside the [-90,90] latitudinal limits.

Value

Returns a dataframe representing the simulated track with columns

segment	track segment
date	time (as GMT POSIXct)
x	x coordinate
y	y coordinate
x.v	x component of velocity
y.v	y component of velocity

SWotherspoon/RWalc documentation built on Feb. 25, 2021, 8:26 p.m.