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#' Compute the \eqn{\alpha^*}{alpha*} value
#'
#' @param coords coordinates of the points for which you want to compute the
#' alphashape
#'
#' @return The \eqn{\alpha^*}{alpha*} value
#' as defined in Gruson (2020).
#'
#' @seealso [alphashape3d::ashape3d()]
#'
#' @keywords internal
#'
#' @references
#' Gruson H. (2020). Estimation of colour volumes as concave hypervolumes using
#' \eqn{\alpha}{alpha}-shapes. Methods in Ecology and Evolution, 11(8), 955-963
#' \doi{10.1111/2041-210X.13398}
find_astar <- function(coords) {
tetras <- alphashape3d::ashape3d(coords,
alpha = 0
)$tetra
tetras <- cbind(
c(tetras[, c("v1", "v2", "v3", "v4")]),
rep(tetras[, "rhoT"], 4)
)
astar <- max(by(tetras[, 2], tetras[, 1], min))
message("'avalue' automatically set to ", sprintf("%.4e", astar * (1 + 1e-15)))
# We have to round the value because of numerical precision issues
return(astar * (1 + 1e-15))
}
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