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Features Controlled by Graphics Objects

Purpose of Graphics Objects

Graphics objects represent data in intuitive and meaningful ways, such as line graphs, images, text, and combinations of these objects. Graphics objects act as containers for other objects or as representations of data.

  • Containers — Figures display all graphics objects. Panels and groups enable collections of objects to be treated as one entity for some operations.

  • Axes are containers that define a coordinate system for the objects that represent the actual data in graphs.

  • Data visualization objects — Lines, text, images, surfaces, and patches that implement various types of graphs.

Figures

Figures are the windows in which MATLAB® displays graphics. Figures contain menus, toolbars, user-interface objects, context menus, and axes.

Figures play two distinct roles in MATLAB:

  • Containing graphs of data

  • Containing user interfaces (which can include graphs in the interface)

Graphics Features Controlled by Figures

Figure properties control certain characteristics that affect graphs:

  • Color and transparency of surfaces and patches — Alphamap and Colormap

  • Appearance of plotted lines and axes grid lines — GraphicsSmoothing

  • Printing and exporting graphs — figure printing properties

  • Drawing speed and rendering features — Renderer

Figures use different drawing methods called renderers. There are two renderers:

  • OpenGL® — The default renderer used by MATLAB for most applications. For more information, see opengl.

  • Painters — Use when OpenGL has problems on a computer with particular graphics hardware that has software defects or outdated software drivers. Also used for exporting graphics for certain formats, such as PDF.

    Note

    For best results, ensure that your computer has the latest graphics hardware drivers supplied by the hardware vendor.

For a list of all figure properties, see Figure Properties

Axes

MATLAB creates an axes to define the coordinate system of each graph. Axes are always contained by a figure object. Axes themselves contain the graphics objects that represent data.

Axes control many aspects of how MATLAB displays graphical information.

Graphics Features Controlled by Axes

Much of what you can customize in a graph is controlled by axes properties.

  • Axis limits, orientation, and tick placement

  • Axis scales (linear or logarithmic)

  • Grid control

  • Font characteristics for the title and axis labels.

  • Default line colors and line styles for multiline graphs

  • Axis line and grid control

  • Color scaling of objects based on colormap

  • View and aspect ratio

  • Clipping graphs to axis limits

  • Controlling axes resize behavior

  • Lighting and transparency control

For a list of all axes properties, see Axes Properties

Objects That Represent Data

Data objects are the lines, images, text, and polygons that graphs use to represent data. For example:

  • Lines connect data points using specified x- and y-coordinates.

  • Markers locate scattered data in some range of values.

  • Rectangular bars indicate distribution of values in a histogram.

Because there are many kinds of graphs, there are many types of data objects. Some are general purpose, such as lines and rectangles and some are highly specialized, such as errorbars, colorbars, and legends.

Graphics Features Controlled by Data Objects

Data object properties control the appearance of the object and also contain the data that defines the object. Data object properties can also control certain behaviors.

  • Data — Change the data to update the graph. Many data objects can link their data properties to workspace variables that contain the data.

  • Color Data — Objects can control how data maps to colors by specifying color data.

  • Appearance — Specify colors of line, markers, polygon faces as well as line styles, marker types.

  • Specific behaviors — Properties can control how the object interprets or displays its data. For example, Bar objects have a property called BarLayout that determines if the bars are grouped or stacked. Contour objects have a LevelList property that specifies the contour intervals at which to draw contour lines.

High-Level vs. Low-Level Functions

Plotting functions create data objects in one of two ways:

  • High-level functions — Create complete graphs that replace existing graphs with new ones. High-level functions include plot, bar, scatter, and so on. For a summary of high-level functions, see Types of MATLAB Plots.

  • Low-level functions — Add graphics objects with minimal changes to the existing graph. Low-level functions include line, patch, rectangle, surface, text, image, and light.

Group Objects

Group objects enable you to treat a number of data objects as one entity. For example, you can make the entire group visible or invisible, select all objects when only one is clicked, or apply a transform matrix to rotate, translate, or scale all the objects in the group.

This code parents the plotted lines to the group object returned by the hggroup function. The text object is not part of the group.

y = magic(5);
hg = hggroup;
plot(y,'Parent',hg)
text(2.5,10,'Plot of 5x5 magic square')

Annotation Objects

Annotation objects comprise arrows, text boxes, and combinations of both. Annotation objects have special features that overcome the limitations of data objects used to annotate graphs:

  • Annotation objects are children of the figure.

  • You can easily locate annotations anywhere in the figure.

  • Define the location of annotation objects in normalized figure coordinates: lower left = (0,0), upper right = (1,1), making their placement independent of range of data represented by the axes.

Note

MATLAB parents annotation objects to a special layer. Do not attempt to parent objects to this layer. MATLAB automatically assigns annotation objects to the appropriate parent.