chull
Convex Hull of a Planar Set of Points

Description

Returns a vector that describes the convex hull(s) of a set of points. Any number of nested convex hulls can be generated, including the entire set.

Usage

chull(x, y=NULL, peel = FALSE, maxpeel = length(x), onbdy = peel, tol = 1e-12)

Arguments

x,y the coordinates of points. The coordinates can be given by two vector arguments or by a single argument, x, which is a times series, a two-column matrix, or a list containing components named x and y. See xy.coords. Missing values are not accepted.
peel a logical value. If TRUE, successive convex hulls are peeled from the remaining points, generating a nested set of hulls. The default is FALSE. This argument is not available in the open-source R chull function.
maxpeel the maximum number of hulls to peel from the data. The default, if peel is TRUE, is to peel until all points are assigned to a hull. If maxpeel is given, peel is set to TRUE. This argument is not available in the open-source R chull function.
onbdy a logical value. If TRUE, points on the boundary of a convex hull (but not vertices of the hull) are included in the hull. This argument is not available in the open-source R chull function.
tol a numeric relative tolerance for determining if a third point is sufficiently collinear to two points in the hull to also include in the hull. This argument is not available in the open-source R chull function.

Details

This function finds the convex hull of a set of points in the plane. It is based on a C translation (by f2c) of ACM Transactions on Mathematical Software (TOMS) algorithm 523 by W. F. Eddy, vol 3 (1977), 398-403, 411-2.
Value
Differences between Spotfire Enterprise Runtime for R and Open-source R
The arguments: peel, maxpeel, onbdy and tol are not available in Open-source R's chull function.
References
Barnett, V. 1976. The ordering of multivariate data. Journal of the Royal Statistical Society, Series A . Volume 139, 318-354.
Eddy, W. F. 1977. Algorithm 523: CONVEX, A New Convex Hull Algorithm for Planar Sets. Journal of ACM Transactions on Mathematical Software (TOMS) Volume 3, 398-403, 411-412.
See Also
xy.coords
Examples
x <- 1:12
y <-  c(0.5, 0.2, -0.3, 3.2, 0, 1, 9, -3, 3, 4, 7, 8)
hull <- chull(x,y) #  hull is:  8  1  7 12

X <- matrix(rnorm(2000), ncol = 2) hpts <- chull(X)

Package grDevices version 6.1.1-7
Package Index