R: alpha-convex hull calculation of tracking data

ahull_track {alphahull} | R Documentation

## alpha-convex hull calculation of tracking data

### Description

This function approximates the α-convex hull of tracking data and returns a list of geom_path objects of the boundary.

### Usage

    ahull_track(x, y = NULL, alpha, nps = 10000, sc = 100)

### Arguments

`x, y` | The `x` and `y` arguments provide the `x` and `y` coordinates of a set of points. Alternatively, a single argument `x` can be provided, see Details.
`alpha` | Value of α.
`nps` | Number of points to generate in each segment connecting two locations, see Details
`sc` | Scale factor.

### Details

An attempt is made to interpret the arguments x and y in a way suitable for computing the α-convex hull. Any reasonable way of defining the coordinates is acceptable, see `xy.coords`.

Increase `nps` if the trajectory is not contained in the computed estimator.

### Value

A list of geom_path objects defining the boundary of the α-convex

### References

Cholaquidis, A., Fraiman, R., Lugosi, G. and Pateiro-Lopez, B. (2014) Set estimation from reflected Brownian motion. arXiv:1411.0433.

Wikelski, M., and Kays, R. (2014). Movebank: archive, analysis and sharing of animal movement data. World Wide Web electronic publication.

### Examples

    ## Not run:
    library(move)
    library(ggmap)
    # Data from Movebank
    # Study Name: Dunn Ranch Bison Tracking Project
    # Principal Investigator: Stephen Blake, Randy Arndt, Doug Ladd
    # Max Planck Institute for Ornithology Radolfzell Germany
    study <- "Dunn Ranch Bison Tracking Project"
    cainfo <- system.file("CurlSSL", "cacert.pem", package = "RCurl")
    options(RCurlOptions = list(verbose = FALSE, capath = cainfo, ssl.verifypeer = FALSE))
    # Login to movebank (first create the login object)
    curl <- movebankLogin(username = "xxx", password = "zzz")
    # Downloads study stored in Movebank
    track <- getMovebankData(study = study, login = curl)
    dat <- track@data[track@data[, "deployment_id"] == 13848432,]
    # Map of animal locations
    bbox <- ggmap::make_bbox(dat[,"location_long"], dat[,"location_lat"], f = 0.3)
    map_loc <- get_map(location = bbox, source = "google", maptype = 'satellite')
    map <- ggmap(map_loc, extent = 'panel', maprange=FALSE)
    p <- map + geom_path(data = dat, aes(x = location_long, y = location_lat), col=2, size=0.3)
    p
    ah_gp <- ahull_track(x = dat[, c("location_long", "location_lat")], alpha = 0.005)
    p + ah_gp

    ## End(Not run)

[Package alphahull version 2.2 Index]