Ternary: Create Ternary and Holdridge Plots

#' Polygon geometry
#'
#' Geometry functions for irregular polygons.
#'
#' @param x,y Vectors containing the coordinates of the vertices of the polygon.
#' @examples
#' x <- c(-3, -1, 6, 3, -4)
#' y <- c(-2, 4, 1, 10, 9)
#' plot(x, y, frame.plot = FALSE)
#' polygon(x, y)
#' @template MRS
#' @family tiling functions
#' @name Polygon-Geometry
NULL

#' @describeIn Polygon-Geometry Calculate the area of an irregular polygon
#' @importFrom grDevices xy.coords
#' @param positive If vertices are specified in an anticlockwise direction,
#' the polygon will be treated as a hole, with a negative area, unless
#' `positive` is set to TRUE.
#' Vertices specified in a clockwise sequence always yield a positive area.
#'
#' @return `PolygonArea()` returns the area of the specified polygon.
#' @examples
#' PolygonArea(x, y)
#' @export
PolygonArea <- PlotTools::PolygonArea

#' @describeIn Polygon-Geometry Locate the centre of a polygon
#' @importFrom grDevices xy.coords
#' @return `PolygonCentre()` returns a single-row matrix containing the
#' _x_ and _y_ coordinates of the geometric centre of the polygon.
#' @examples
#' points(PolygonCentre(x, y), pch = 3, cex = 2)
#' @export
PolygonCentre <- PlotTools::PolygonCentre

#' @rdname Polygon-Geometry
#' @export
PolygonCenter <- PolygonCentre


#' @describeIn Polygon-Geometry Enlarge a polygon in all directions
#'
#' @param buffer Numeric specifying distance by which to grow polygon.
#' @return `GrowPolygon()` returns coordinates of the vertices of `polygon`
#' after moving each vertex `buffer` away from the polygon's centre.
#' @importFrom grDevices xy.coords
#' @examples
#' polygon(GrowPolygon(x, y, 1), border = "darkgreen",
#'         xpd = NA # Allow drawing beyond plot border
#'        )
#'
#' # Negative values shrink the polygon
#' polygon(GrowPolygon(x, y, -1), border = "red")
#' @export
GrowPolygon <- PlotTools::GrowPolygon