poly2fv

Convert polygon coordinates to patch faces and vertices

Syntax

[F,V] = poly2fv(x,y)

Description

[F,V] = poly2fv(x,y) converts the polygon coordinates defined by x and y into the triangular polygon regions defined by V and F, where V contains the vertices and F determines the vertices to connect.

You can use the outputs of this function to display polygon regions by using the patch function.

Examples

Convert Coordinates to Patch Faces and Vertices

Specify the xy-coordinates of three polygons:

• A rectangle with vertices in a clockwise order.

• A square with vertices in a counterclockwise order.

• A triangle with vertices in a counterclockwise order.

x1 = [0 0 6 6 0];
y1 = [0 3 3 0 0];
x2 = [1 2 2 1 1];
y2 = [1 1 2 2 1];
x3 = [4 5 4 4];
y3 = [1 1 2 1];

Convert the coordinates to patch faces and vertices.

[F,V] = poly2fv({x1,x2,x3},{y1,y2,y3});

Display the patch.

figure
patch("Faces",F,"Vertices",V,"FaceColor","r","EdgeColor","none")
axis equal

Input Arguments

x — x-coordinates of polygon

numeric vector | cell array of numeric vectors

x-coordinates of the polygon, specified as a numeric vector or a cell array of numeric vectors.

• Define one polygon by specifying a vector, such as [39 45 19 39].

• Define multiple polygons by using one of these options:

  • Specify a vector and separate the polygons using NaN values, such as [37 46 31 20 37 NaN 45 49 35 32 45 NaN 35 40 42 35]. The NaN values in x must correspond to the NaN values in y.

  • Specify a cell array of vectors, such as {[37 46 31 20 37],[45 49 35 32 45],[35 40 42 35]}. The size of the vector in each cell of x must match the size of the vector in the corresponding cell of y.

The size and type of x must match the size and type of y.

y — y-coordinates of polygon

numeric vector | cell array of numeric vectors

y-coordinates of the polygon, specified as a numeric vector or a cell array of numeric vectors.

• Define one polygon by specifying a vector, such as [-113 -49 -100 -113].

• Define multiple polygons by using one of these options:

  • Specify a vector and separate the polygons using NaN values, such as [69 90 105 79 69 NaN 6 52 43 14 6 NaN 18 32 22 18]. The NaN values in y must correspond to the NaN values in x.

  • Specify a cell array of vectors, such as {[69 90 105 79 69],[6 52 43 14 6],[18 32 22 18]}. The size of the vector in each cell of y must match the size of the vector in the corresponding cell of x.

The size and type of y must match the size and type of x.

Output Arguments

F — Polygon face definitions

three-column matrix

Polygon face definitions, returned as a three-column matrix that determines which vertices in V to connect. The poly2fv function creates triangular faces.

Data Types: double

V — Polygon vertices

two-column matrix

Polygon vertices, returned as a two-column matrix. Each row of the matrix contains the xy-coordinates of a vertex.

Data Types: double

Tips

Most Mapping Toolbox™ functions assume that clockwise-ordered vertices define external polygon edges and counterclockwise-ordered vertices define internal polygon edges. Although the poly2fv function ignores vertex order, you can ensure consistency with other functions by following this convention.

Version History

Introduced before R2006a

R2019b: Order of polygon vertices might be different

The poly2fv function might return polygon vertices in a different order. The polygons that these vertices define are geometrically equivalent to those in previous releases.