MATLAB Function Reference |

**Syntax**

**Description**

```
K = convhull(x,y)
```

returns indices into the `x`

and `y`

vectors of the points on the convex hull.

`K = convhull(x,y,options)`

specifies a cell array of strings `options`

to be used in Qhull via `convhulln`

. The default option is `{'Qt'}`

.

If `options`

is `[]`

, the default options are used. If `options`

is `{''}`

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

```
[K,a] = convhull(...)
```

also returns the area of the convex hull.

**Visualization**

Use `plot`

to plot the output of `convhull`

.

**Examples**

xx = -1:.05:1; yy = abs(sqrt(xx)); [x,y] = pol2cart(xx,yy); k = convhull(x,y); plot(x(k),y(k),'r-',x,y,'b+')

**Example 2.** The following example illustrates the `options`

input for `convhull`

. 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 this warning, use the option `'Pp'`

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

, along with the default `'Qt'`

, to `convhull`

.

**Algorithm**

`convhull`

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 **

`convhulln`

, `delaunay`

, `plot`

, `polyarea`

, `voronoi`

**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.

conv2 | convhulln |

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