working/areaFromPointsOrPoly.r

In adamlilith/enmSdm: Tools for Modeling Niches and Distributions of Species

#' Area of a spatial polygon or set of points
#'
#' @description This function returns the area of a spatial polygon, \emph{or} of the minimum convex polygon of a set of points. Input can be a set of coordinates or a polygon.
#' @param x		Any of: SpatialPoints, SpatialPointsDataFrame, SpatialPolygons, or SpatialPolygonsDataFrame. Must be in an equal-area projection!
#' @return		Numeric (area in km2).
#' @export
areaFromPointsOrPoly <- function(x) {

	# minimum convex polygon
	if (inherits(x, 'Spatial')) {
		x <- adehabitatHR::mcp(x, percent=100, unout='km2')
	} else {
		stop('"x" must be a Spatial* object.')
	}

	# area of MCP
	area_m2 <- rgeos::gArea(x)
	area_km2 <- area_m2 / 1000^2

	area_km2
	
}