grDevices (version 3.3.1)

chull: Compute Convex Hull of a Set of Points


Computes the subset of points which lie on the convex hull of the set of points specified.


chull(x, y = NULL)


x, y
coordinate vectors of points. This can be specified as two vectors x and y, a 2-column matrix x, a list x with two components, etc, see xy.coords.


An integer vector giving the indices of the unique points lying on the convex hull, in clockwise order. (The first will be returned for duplicate points.)


xy.coords is used to interpret the specification of the points. Infinite, missing and NaN values are not allowed.

The algorithm is that given by Eddy (1977).


Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

Eddy, W. F. (1977) A new convex hull algorithm for planar sets. ACM Transactions on Mathematical Software, 3, 398--403.

Eddy, W. F. (1977) Algorithm 523. CONVEX, A new convex hull algorithm for planar sets[Z]. ACM Transactions on Mathematical Software, 3, 411--412.

See Also

xy.coords, polygon


Run this code
X <- matrix(stats::rnorm(2000), ncol = 2)
## Not run: 
#   # Example usage from graphics package
#   plot(X, cex = 0.5)
#   hpts <- chull(X)
#   hpts <- c(hpts, hpts[1])
#   lines(X[hpts, ])
# ## End(Not run)

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