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A Voronoi diagram or Voronoi tessellation of a set of points `s` in
an N-dimensional space, is the tessellation of the N-dimensional space
such that all points in

, a partitions of the
tessellation where `v`(`p`)`p` is a member of `s`, are closer to `p`
than any other point in `s`. The Voronoi diagram is related to the
Delaunay triangulation of a set of points, in that the vertexes of the
Voronoi tessellation are the centers of the circum-circles of the
simplices of the Delaunay tessellation.

- Function File:
**voronoi***(*`x`,`y`) - Function File:
**voronoi***(*`x`,`y`,`options`) - Function File:
**voronoi***(…, "linespec")* - Function File:
**voronoi***(*`hax`, …) - Function File:
`h`=**voronoi***(…)* - Function File:
*[*`vx`,`vy`] =**voronoi***(…)* Plot the Voronoi diagram of points

`(`

. The Voronoi facets with points at infinity are not drawn.`x`,`y`)If

`"linespec"`

is given it is used to set the color and line style of the plot. If an axis graphics handle`hax`is supplied then the Voronoi diagram is drawn on the specified axis rather than in a new figure.The

`options`argument, which must be a string or cell array of strings, contains options passed to the underlying qhull command. See the documentation for the Qhull library for details http://www.qhull.org/html/qh-quick.htm#options.If a single output argument is requested then the Voronoi diagram will be plotted and a graphics handle

`h`to the plot is returned. [`vx`,`vy`] = voronoi (…) returns the Voronoi vertices instead of plotting the diagram.x = rand (10, 1); y = rand (size (x)); h = convhull (x, y); [vx, vy] = voronoi (x, y); plot (vx, vy, "-b", x, y, "o", x(h), y(h), "-g"); legend ("", "points", "hull");

- Function File:
*[*`C`,`F`] =**voronoin***(*`pts`) - Function File:
*[*`C`,`F`] =**voronoin***(*`pts`,`options`) Compute N-dimensional Voronoi facets. The input matrix

`pts`of size [n, dim] contains n points in a space of dimension dim.`C`contains the points of the Voronoi facets. The list`F`contains, for each facet, the indices of the Voronoi points.An optional second argument, which must be a string or cell array of strings, contains options passed to the underlying qhull command. See the documentation for the Qhull library for details http://www.qhull.org/html/qh-quick.htm#options.

The default options depend on the dimension of the input:

- 2-D and 3-D:
`options`=`{"Qbb"}`

- 4-D and higher:
`options`=`{"Qbb", "Qx"}`

If

`options`is not present or`[]`

then the default arguments are used. Otherwise,`options`replaces the default argument list. To append user options to the defaults it is necessary to repeat the default arguments in`options`. Use a null string to pass no arguments.- 2-D and 3-D:

An example of the use of `voronoi`

is

rand ("state",9); x = rand (10,1); y = rand (10,1); tri = delaunay (x, y); [vx, vy] = voronoi (x, y, tri); triplot (tri, x, y, "b"); hold on; plot (vx, vy, "r");

The result of which can be seen in Figure 30.3. Note that the circum-circle of one of the triangles has been added to this figure, to make the relationship between the Delaunay tessellation and the Voronoi diagram clearer.

Additional information about the size of the facets of a Voronoi
diagram, and which points of a set of points is in a polygon can be had
with the `polyarea`

and `inpolygon`

functions respectively.

- Function File:
**polyarea***(*`x`,`y`) - Function File:
**polyarea***(*`x`,`y`,`dim`) -
Determine area of a polygon by triangle method. The variables

`x`and`y`define the vertex pairs, and must therefore have the same shape. They can be either vectors or arrays. If they are arrays then the columns of`x`and`y`are treated separately and an area returned for each.If the optional

`dim`argument is given, then`polyarea`

works along this dimension of the arrays`x`and`y`.

An example of the use of `polyarea`

might be

rand ("state", 2); x = rand (10, 1); y = rand (10, 1); [c, f] = voronoin ([x, y]); af = zeros (size (f)); for i = 1 : length (f) af(i) = polyarea (c (f {i, :}, 1), c (f {i, :}, 2)); endfor

Facets of the Voronoi diagram with a vertex at infinity have infinity
area. A simplified version of `polyarea`

for rectangles is
available with `rectint`

- Function File:
`area`=**rectint***(*`a`,`b`) -
Compute the area of intersection of rectangles in

`a`and rectangles in`b`. Rectangles are defined as [x y width height] where x and y are the minimum values of the two orthogonal dimensions.If

`a`or`b`are matrices, then the output,`area`, is a matrix where the i-th row corresponds to the i-th row of a and the j-th column corresponds to the j-th row of b.**See also:**polyarea.

- Function File:
*[*`in`,`on`] =**inpolygon***(*`x`,`y`,`xv`,`yv`) -
For a polygon defined by vertex points

`(`

, determine if the points`xv`,`yv`)`(`

are inside or outside the polygon. The variables`x`,`y`)`x`,`y`, must have the same dimension. The optional output`on`gives the points that are on the polygon.

An example of the use of `inpolygon`

might be

randn ("state", 2); x = randn (100, 1); y = randn (100, 1); vx = cos (pi * [-1 : 0.1: 1]); vy = sin (pi * [-1 : 0.1 : 1]); in = inpolygon (x, y, vx, vy); plot (vx, vy, x(in), y(in), "r+", x(!in), y(!in), "bo"); axis ([-2, 2, -2, 2]);

The result of which can be seen in Figure 30.4.

Next: Convex Hull, Previous: Delaunay Triangulation, Up: Geometry [Contents][Index]