Default movement model for path sampling

Return the calibrated movement model used by default in sampling_path(). Call sampling_path_default_movement() to inspect its values, plot it with plot_movement(), or modify some fields before passing it to sampling_path(movement = ).

Usage

sampling_path_default_movement()

Value

A movement list with fields method, shape, scale, low_speed_fix, zero_speed_ratio, move_stay_parameters, and move_stay.

Details

The movement model defines the daily transition between consecutive stationary periods. It is a list with two parts.

Ground-speed kernel. The fields method, shape, scale, low_speed_fix and zero_speed_ratio are passed to GeoPressureR::speed2prob() and follow the convention of GeoPressureR::graph_set_movement(). Speed is the great-circle displacement between two consecutive periods divided by 24 h, in km/h. With method = "gamma", the speed density is a Gamma distribution with shape shape and scale scale (km/h). The probability of moving to a given cell is this density divided by the distance and multiplied by cos(latitude), which accounts for the number and area of cells at that distance. The hard movement radius is set separately by sampling_path(thr_gs = ).

Residence-dependent departure. move_stay is a function of the residence t, the number of consecutive transitions spent at the current location (0 for the first transition after arrival), returning the probability of departing at the next transition. The default is the exponential decline to a plateau p_inf + (p_0 - p_inf) * exp(-t / tau). move_stay_parameters stores p_0, p_inf and tau so that plot_movement() can annotate them; it is not used by the sampler, so update move_stay when changing them.

The optional field approx_eps (default 1e-6) drops movement-kernel weights below this value from the precomputed neighbourhood.

The default values were calibrated on multi-sensor reference trajectories of land birds (Gamma shape 1.26 and scale 10.3 km/h; p_0 = 0.607, p_inf = 0.137, tau = 0.932). They should not be assumed to transfer to other taxa.

See also

Other sampling_path: plot_movement(), sampling_path(), sampling_path_diagnostic()

Examples

movement <- sampling_path_default_movement()
str(movement)
#> List of 7
#>  $ method              : chr "gamma"
#>  $ shape               : num 1.26
#>  $ scale               : num 10.3
#>  $ low_speed_fix       : num 0.001
#>  $ zero_speed_ratio    : num 0
#>  $ move_stay_parameters:List of 3
#>   ..$ p_0  : num 0.607
#>   ..$ p_inf: num 0.137
#>   ..$ tau  : num 0.932
#>  $ move_stay           :function (t)  
plot_movement(movement)