grDevices (version 3.6.2)

# 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. 10.1145/355759.355766.

Eddy, W. F. (1977). Algorithm 523: CONVEX, A new convex hull algorithm for planar sets [Z]. ACM Transactions on Mathematical Software, 3, 411--412. 10.1145/355759.355768.

`xy.coords`, `polygon`

## Examples

Run this code
``````# NOT RUN {
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, ])
# }
``````

Run the code above in your browser using DataCamp Workspace