walker {stppSim}

A landscape walker

Description

A dynamic object capable of moving and avoiding obstacles on a landscape.

Usage

walker(n = 5, s_threshold = 250, step_length = 20,
poly = NULL, restriction_feat=NULL, field = NA, coords=c(0,0),
pt_itx = TRUE, show.plot = FALSE)

Arguments

n

number of events to be generated by a walker within a temporal bin.

s_threshold

defines the spatial perception range of a walker at a given location. Default: 250 (in the same linear unit as the poly - polygon shapefile).

step_length

the maximum step taken by a walker from one point to the next.

poly

(An sf or S4 object) a polygon shapefile defining the extent of the landscape

restriction_feat

(An S4 object) optional shapefile containing features in which walkers cannot walk through. Default: NULL.

field

a number in the range of [0-1] (i.e. restriction values) assigned to all features; or the name of a numeric field to extract such restriction values for different classes of feature. Restriction value 0 and 1 indicate the lowest and the highest obstructions, respectively. Default: NULL.

coords

a vector of the form c(x, y) giving the initial coordinates of a walker (i.e., coordinates of origins). Default value is c(0,0) for an arbitrary square space.

pt_itx

To check whether any of the specified initial origin coordinates falls outside the boundary. Default: TRUE.

show.plot

(TRUE or False) To show the time series plot. Default is FALSE.

Details

A walker is propelled by an in-built stochastic transition matrix and a specified set of spatial and temporal parameters. The transition matrix defines two states, namely; the exploratory and a performative states. A walker is capable of avoiding obstructions (i.e., restriction_feat) if included. The resulting number of events may be slightly different from the value n because of the stochastic process involved.

Value

Returns a trace of walker's path, and the resulting events.

References

Quaglietta L, Porto M (2019). SiMRiv: Individual-Based, Spatially-Explicit Simulation and Analysis of Multi-State Movements in River Networks and Heterogeneous Landscapes_. R package version 1.0.4, <URL: https://CRAN.R-project.org/package=SiMRiv>.

Examples

#load boundary of Camden
load(file = system.file("extdata", "camden.rda",
package="stppSim"))
boundary = camden$boundary # get boundary
walkerpath <- walker(n = 5, s_threshold = 250, step_length = 20,
poly = boundary, restriction_feat=NULL, field = NULL,
coords = c(0,0), pt_itx = TRUE, show.plot = FALSE)
#plot(walkerpath)