grDevices (version 3.3.1)

# chull: Compute Convex Hull of a Set of Points

## Description

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

## Usage

`chull(x, y = NULL)`

## Arguments

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`.

## Value

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.)

## Details

`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).

## References

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.

`xy.coords`, `polygon`

## Examples

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

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