patch (MATLAB Functions)

Create patch graphics object

Syntax

patch(X,Y,C)
patch(X,Y,Z,C)
patch(FV)
patch(...'PropertyName',PropertyValue...)
patch('PropertyName',PropertyValue...) PN/PV pairs only
handle = patch(...)

Description

patch is the low-level graphics function for creating patch graphics objects. A patch object is one or more polygons defined by the coordinates of its vertices. You can specify the coloring and lighting of the patch. See Creating 3-D Models with Patches for more information on using patch objects.

patch(X,Y,C) adds the filled two-dimensional patch to the current axes. The elements of X and Y specify the vertices of a polygon. If X and Y are matrices, MATLAB draws one polygon per column. C determines the color of the patch. It can be a single ColorSpec, one color per face, or one color per vertex (see "Remarks"). If C is a 1-by-3 vector, it is assumed to be an RGB triplet, specifying a color directly.

patch(X,Y,Z,C) creates a patch in three-dimensional coordinates.

patch(FV) creates a patch using structure FV, which contains the fields vertices, faces, and optionally facevertexdata. These fields correspond to the Vertices, Faces, and FaceVertexCData patch properties.

patch(...'PropertyName',PropertyValue...) follows the X, Y, (Z), and C arguments with property name/property value pairs to specify additional patch properties.

patch('PropertyName',PropertyValue,...) specifies all properties using property name/property value pairs. This form enables you to omit the color specification because MATLAB uses the default face color and edge color unless you explicitly assign a value to the FaceColor and EdgeColor properties. This form also allows you to specify the patch using the Faces and Vertices properties instead of x-, y-, and z-coordinates. See the "Examples" section for more information.

handle = patch(...) returns the handle of the patch object it creates.

Remarks

Unlike high-level area creation functions, such as fill or area, patch does not check the settings of the figure and axes NextPlot properties. It simply adds the patch object to the current axes.

If the coordinate data does not define closed polygons, patch closes the polygons. The data can define concave or intersecting polygons. However, if the edges of an individual patch face intersect themselves, the resulting face may or may not be completely filled. In that case, it is better to break up the face into smaller polygons.

Specifying Patch Properties

You can specify properties as property name/property value pairs, structure arrays, and cell arrays (see the set and get reference pages for examples of how to specify these data types).

There are two patch properties that specify color:

CData -- Use when specifying x-, y-, and z-coordinates (XData, YData, ZData).
FaceVertexCData -- Use when specifying vertices and connection matrix (Vertices and Faces).

The CData and FaceVertexCData properties accept color data as indexed or true color (RGB) values. See the CData and FaceVertexCData property descriptions for information on how to specify color.

Indexed color data can represent either direct indices into the colormap or scaled values that map the data linearly to the entire colormap (see the caxis function for more information on this scaling). The CDataMapping property determines how MATLAB interprets indexed color data.

Color Data Interpretation

You can specify patch colors as

A single color for all faces
One color for each face, enabling flat coloring
One color for each vertex, enabling interpolated coloring

The following tables summarize how MATLAB interprets color data defined by the CData and FaceVertexCData properties.

Interpretation of the CData Property

[X,Y,Z]Data
CData Required for
Results Obtained

Dimensions
Indexed
True Color

m-by-n
scalar
1-by-1-by-3
Use the single color specified for all patch faces. Edges can be only a single color.

m-by-n
1-by-n
(n >= 4)
1-by-n-by-3
Use one color for each patch face. Edges can be only a single color.

m-by-n
m-by-n
m-by-n-3
Assign a color to each vertex. Patch faces can be flat (a single color) or interpolated. Edges can be flat or interpolated.

[X,Y,Z]Data	CData Required for	Results Obtained
Dimensions	Indexed	True Color
m-by-n	scalar	1-by-1-by-3	Use the single color specified for all patch faces. Edges can be only a single color.
m-by-n	1-by-n (n >= 4)	1-by-n-by-3	Use one color for each patch face. Edges can be only a single color.
m-by-n	m-by-n	m-by-n-3	Assign a color to each vertex. Patch faces can be flat (a single color) or interpolated. Edges can be flat or interpolated.

Vertices
Faces
FaceVertexCData Required for
Results Obtained

Dimensions
Dimensions
Indexed
True Color

m-by-n
k-by-3
scalar
1-by-3
Use the single color specified for all patch faces. Edges can be only a single color.

m-by-n
k-by-3
k-by-1
k-by-3
Use one color for each patch face. Edges can be only a single color.

m-by-n
k-by-3
m-by-1
m-by-3
Assign a color to each vertex. Patch faces can be flat (a single color) or interpolated. Edges can be flat or interpolated.

Interpretation of the FaceVertexCData Property

Vertices	Faces	FaceVertexCData Required for	Results Obtained
Dimensions	Dimensions	Indexed	True Color
m-by-n	k-by-3	scalar	1-by-3	Use the single color specified for all patch faces. Edges can be only a single color.
m-by-n	k-by-3	k-by-1	k-by-3	Use one color for each patch face. Edges can be only a single color.
m-by-n	k-by-3	m-by-1	m-by-3	Assign a color to each vertex. Patch faces can be flat (a single color) or interpolated. Edges can be flat or interpolated.

Examples

This example creates a patch object using two different methods:

Specifying x-, y-, and z-coordinates and color data (XData, YData, ZData, and CData properties)

Specifying vertices, the connection matrix, and color data (Vertices, Faces, FaceVertexCData, and FaceColor properties)

Specifying X, Y, and Z Coordinates

The first approach specifies the coordinates of each vertex. In this example, the coordinate data defines two triangular faces, each having three vertices. Using true color, the top face is set to white and the bottom face to gray.

x = [0 0;0 1;1 1]; y = [1 1;2 2;2 1]; z = [1 1;1 1;1 1]; tcolor(1,1,1:3) = [1 1 1]; tcolor(1,2,1:3) = [.7 .7 .7]; patch(x,y,z,tcolor)

Notice that each face shares two vertices with the other face (V₁-V₄ and V₃-V₅).

Specifying Vertices and Faces

The Vertices property contains the coordinates of each unique vertex defining the patch. The Faces property specifies how to connect these vertices to form each face of the patch. For this example, two vertices share the same location so you need to specify only four of the six vertices. Each row contains the x-, y-, and z-coordinates of each vertex.

vert = [0 1 1;0 2 1;1 2 1;1 1 1];

There are only two faces, defined by connecting the vertices in the order indicated.

fac = [1 2 3;1 3 4];

To specify the face colors, define a 2-by-3 matrix containing two RGB color definitions.

tcolor = [1 1 1;.7 .7 .7];

With two faces and two colors, MATLAB can color each face with flat shading. This means you must set the FaceColor property to flat, since the faces/vertices technique is available only as a low-level function call (i.e., only by specifying property name/property value pairs).

Create the patch by specifying the Faces, Vertices, and FaceVertexCData properties as well as the FaceColor property.

patch('Faces',fac,'Vertices',vert,'FaceVertexCData',tcolor,... 'FaceColor','flat')

Specifying only unique vertices and their connection matrix can reduce the size of the data for patches having many faces. See the descriptions of the Faces, Vertices, and FaceVertexCData properties for information on how to define them.

MATLAB does not require each face to have the same number of vertices. In cases where they do not, pad the Faces matrix with NaNs. To define a patch with faces that do not close, add one or more NaNs to the row in the Vertices matrix that defines the vertex you do not want connected.

Object Hierarchy

Setting Default Properties

You can set default patch properties on the axes, figure, and root levels:

set(0,'DefaultPatchPropertyName',PropertyValue...) set(gcf,'DefaultPatchPropertyName',PropertyValue...) set(gca,'DefaultPatchPropertyName',PropertyValue...)

PropertyName is the name of the patch property and PropertyValue is the value you are specifying. Use set and get to access patch properties.

See Also

area, caxis, fill, fill3, isosurface, surface

Object Creation Functions for related functions

Patch Properties for property descriptions

Creating 3-D Models with Patches for examples that use patches

pascal Patch Properties

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