Provide facilities for 2D graphical output


This class provides facilities for producing 2D graphical output. A Plot is a specialised form of FrameSet, in which the base Frame describes a " graphical" coordinate system and is associated with a rectangular plotting area in the underlying graphics system. This plotting area is where graphical output appears. It is defined when the Plot is created.

The current Frame of a Plot describes a " physical" coordinate system, which is the coordinate system in which plotting operations are specified. The results of each plotting operation are automatically transformed into graphical coordinates so as to appear in the plotting area (subject to any clipping which may be in effect).

Because the Mapping between physical and graphical coordinates may often be non-linear, or even discontinuous, most plotting does not result in simple straight lines. The basic plotting element is therefore not a straight line, but a geodesic curve (see astCurve, astGenCurve and astPolyCurve). A Plot also provides facilities for drawing markers or symbols (astMark), text (astText) and grid lines (astGridLine). It is also possible to draw curvilinear axes with optional coordinate grids (astGrid). A range of Plot attributes is available to allow precise control over the appearance of graphical output produced by these functions.

You may select different physical coordinate systems in which to plot (including the native graphical coordinate system itself) by selecting different Frames as the current Frame of a Plot, using its Current attribute. You may also set up clipping (see astClip) to limit the extent of any plotting you perform, and this may be done in any of the coordinate systems associated with the Plot, not necessarily the one you are plotting in.

Like any FrameSet, a Plot may also be used as a Frame. In this case, it behaves like its current Frame, which describes the physical coordinate system.

When used as a Mapping, a Plot describes the inter-relation between graphical coordinates (its base Frame) and physical coordinates (its current Frame). It differs from a normal FrameSet, however, in that an attempt to transform points which lie in clipped areas of the Plot will result in bad coordinate values (AST__BAD).

Constructor Function



The Plot class inherits from the FrameSet class.


In addition to those attributes common to all FrameSets, every Plot also has the following attributes:


In addition to those functions applicable to all FrameSets, the following functions may also be applied to all Plots:

Graphical Elements

The colour index, character font, character size, line style and line width used for plotting can be set independently for various elements of the graphical output produced by a Plot. The different graphical elements are identified by appending the strings listed below as subscripts to the Plot attributes Colour(element), Font(element), Size(element), Style(element) and Width(element). These strings are case-insensitive and unambiguous abbreviations may be used. Elements of the graphical output which relate to individual axes can be referred to either independently (e.g. " (Grid1)" and " (Grid2)" ) or together (e.g. " (Grid)" ):