# convex.hull: Return the convex hull of a triangulation object In tripack: Triangulation of Irregularly Spaced Data

## Description

Given a triangulation `tri.obj` of n points in the plane, this subroutine returns two vectors containing the coordinates of the nodes on the boundary of the convex hull.

## Usage

 `1` ```convex.hull(tri.obj, plot.it=FALSE, add=FALSE,...) ```

## Arguments

 `tri.obj` object of class `"tri"` `plot.it` logical, if `TRUE` the convex hull of `tri.obj` will be plotted. `add` logical. if `TRUE` (and `plot.it=TRUE`), add to a current plot. `...` additional plot arguments

## Value

 `x` x coordinates of boundary nodes. `y` y coordinates of boundary nodes.

A. Gebhardt

## References

R. J. Renka (1996). Algorithm 751: TRIPACK: a constrained two-dimensional Delaunay triangulation package. ACM Transactions on Mathematical Software. 22, 1-8.

`tri`, `print.tri`, `plot.tri`, `summary.tri`, `triangles`, `add.constraint`.
 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15``` ```# rather simple example from TRIPACK: data(tritest) tr<-tri.mesh(tritest\$x,tritest\$y) convex.hull(tr,plot.it=TRUE) # random points: rand.tr<-tri.mesh(runif(10),runif(10)) plot(rand.tr) rand.ch<-convex.hull(rand.tr, plot.it=TRUE, add=TRUE, col="red") # use a part of the quakes data set: data(quakes) quakes.part<-quakes[(quakes[,1]<=-17 & quakes[,1]>=-19.0 & quakes[,2]<=182.0 & quakes[,2]>=180.0),] quakes.tri<-tri.mesh(quakes.part\$lon, quakes.part\$lat, duplicate="remove") plot(quakes.tri) convex.hull(quakes.tri, plot.it=TRUE, add=TRUE, col="red") ```