View source: R/getDynamicAlphaHull.R

getDynamicAlphaHull | R Documentation |

Generates an apha hull polygon, where the alpha parameter is determined by the spatial distribution of the coordinates.

getDynamicAlphaHull( x, fraction = 0.95, partCount = 3, buff = 10000, initialAlpha = 3, coordHeaders = c("Longitude", "Latitude"), clipToCoast = "terrestrial", alphaIncrement = 1, verbose = FALSE, alphaCap = 400 )

`x` |
dataframe of coordinates in decimal degrees, with a minimum of 3 rows. |

`fraction` |
the minimum fraction of occurrences that must be included in polygon. |

`partCount` |
the maximum number of disjunct polygons that are allowed. |

`buff` |
buffering distance in meters |

`initialAlpha` |
the starting value for alpha |

`coordHeaders` |
the column names for the longitude and latitude
columns, respectively. If x has two columns, these are assumed to be
longitude and latitude, and |

`clipToCoast` |
Either "no" (no clipping), "terrestrial" (only terrestrial part of range is kept) or "aquatic" (only non-terrestrial part is clipped). See Details. |

`alphaIncrement` |
the amount to increase alpha with each iteration |

`verbose` |
prints the alpha value to the console, intended for debugging. |

`alphaCap` |
Max alpha value before function aborts and returns a minimum convex hull. |

From a set of coordinates, this function will create an alpha hull with
`alpha = initialAlpha`

, and will then increase `alpha`

by
`alphaIncrement`

until both the `fraction`

and `partCount`

conditions are met.

If the conditions cannot be satisfied, then a minimum convex hull is returned.

If `clipToCoast`

is set to "terrestrial" or "aquatic", the resulting
polygon is clipped to the coastline, using a basemap from naturalearth.
The first time this function is run, this basemap will be downloaded.
Subsequent calls will use the downloaded map.

a list with 2 elements:

`hull` |
a sf polygon object |

`alpha` |
the alpha value that was found to satisfy the criteria. If a convex hull was returned, this will list MCH. |

Pascal Title

Alpha hulls are created with `ahull`

.

data(crotalus) # create a polygon range for Crotalus atrox x <- crotalus[which(crotalus$genSp == 'Crotalus_atrox'),] x <- x[sample(1:nrow(x), 50),] range <- getDynamicAlphaHull(x, coordHeaders=c('decimallongitude','decimallatitude'), clipToCoast = 'no') plot(range[[1]], col=transparentColor('dark green', 0.5), border = NA) points(x[,c('decimallongitude','decimallatitude')], cex = 0.5, pch = 3) # to add a basic coastline, you can use the internal map # world <- rangeBuilder:::loadWorldMap() # plot(world, add = TRUE, lwd = 0.5)

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