MATLAB Function Reference |

**Syntax**

**Description**

```
K = convhulln(X)
```

returns the indices `K`

of the points in `X`

that comprise the facets of the convex hull of `X`

. `X`

is an `m`

-by-`n`

array representing `m`

points in N-dimensional space. If the convex hull has `p`

facets then `K`

is `p`

-by-`n`

.

`K = convulln(X, options)`

specifies a cell array of strings `options`

to be used as options in Qhull. The default options are:

If `options`

is `[]`

, the default options are used. If `options`

is `{''}`

, no options are used, not even the default. For more information on Qhull and its options, see http://www.qhull.org/.

`[K, v] = convhulln(...)`

also returns the volume `v`

of the convex hull.

**Visualization**

Plotting the output of `convhulln`

depends on the value of `n`

:

- For
`n = 2`

, use`plot`

as you would for`convhull`

. - For
`n = 3`

, you can use`trisurf`

to plot the output. The calling sequence is

For more control over the color of the facets, use

`patch`

to plot the output. For an example, see Tessellation and Interpolation of Scattered Data in Higher Dimensions in the MATLAB documentation.

**Example**

The following example illustrates the `options`

input for `convhulln`

. The following commands

Warning: qhull precision warning: The initial hull is narrow (cosine of min. angle is 0.9999999999999998). A coplanar point may lead to a wide facet. Options 'QbB' (scale to unit box) or 'Qbb' (scale last coordinate) may remove this warning. Use 'Pp' to skip this warning.

To suppress the warning, use the option `'Pp'`

.The following command passes the option `'Pp'`

, along with the default `'Qt'`

, to `convhulln`

.

**Algorithm**

`convhulln`

is based on Qhull [2]. For information about Qhull, see http://www.qhull.org/. For copyright information, see http://www.qhull.org/COPYING.txt.

**See Also**

`convhull`

, `delaunayn`

, `dsearchn`

, `tsearchn`

, `voronoin`

**Reference**

[1] Barber, C. B., D.P. Dobkin, and H.T. Huhdanpaa, "The Quickhull Algorithm for
Convex Hulls," *ACM Transactions on Mathematical Software*, Vol. 22, No. 4,
Dec. 1996, p. 469-483. Available in PDF format at http://www.acm.org/pubs/
citations/journals/toms/1996-22-4/p469-barber/.

[2] National Science and Technology Research Center for Computation and Visualization of Geometric Structures (The Geometry Center), University of Minnesota. 1993.

convhull | convn |

© 1994-2005 The MathWorks, Inc.