JMSL Chart Programmer's Guide

2D Drawing Elements >> AxisXY

AxisXY

The AxisXY node is the basis of many chart types, including scatter, line, area and error bar. Its parent node must be the root Chart node.

When an AxisXY node is created, it creates two Axis1D nodes. They can be obtained by using the methods AxisXY.getAxisX() and AxisXY.getAxisY() . Each of the Axis1D nodes in turn creates additional child nodes, as seen in the diagram below.

Accessor methods can be chained together, so the x-axis line can be retrieved using

axis.getAxisX().getAxisLine()

The code to set the x-axis line to blue is

axis.getAxisX().getAxisLine().setLineColor(Color.blue)

Axis Layout

The layout of an AxisXY chart, such as the one below, is controlled by the attributes Window, Density, and Number.

Window

Window is a double-array-valued attribute that contains the axis limits. Its value is {min, max}. For the above chart, the value of the Window attribute for the x-axis is [0, 3] and for the y-axis it is [1, 8].

Number

Number is an integer-valued attribute that contains the number of major tick marks along an axis. In an Axis1D node its default value is 5, which is also the value in the above example.

Density

Density is the number of minor tick marks per major tick mark. Its default value is 4, which is also the value in the example.

Transform

The x- and y-axes may be linear, logarithmic, or customized, as specified by the Transform attribute. This attribute can have the values:

• TRANSFORM_LINEAR indicating a linear axis. This is the default.
• TRANSFORM_LOG indicating a logarithmic axis
• TRANSFORM_CUSTOM indicating a custom transformation. The transformation specified by the CustomTransform attribute is used.

CustomTransform

A customized transformation is used when the Transform attribute has the value TRANSFORM_CUSTOM. A custom transform is an object implementing the Transform interface. It defines a mapping from the interval specified by the Window attribute to and from the interval [0,1]. See Custom Transform for more information.

The class TransformDate implements the Transform interface. It maps from a regular calendar to one without weekends, which is useful for charting stock prices that are defined only on weekdays.

Autoscale

Autoscaling is used to automatically determine the attribute Window (the range of numbers along an axis) and the attribute Number (the number of major tick marks). The goal is to adjust the attributes so that the data fits on the axes and the axes have "nice" numbers as labels.

Autoscaling is done in two phases. In the first ("input") phase the actual range is determined. In the second ("output") phase chart attributes are updated.

Attribute AutoscaleInput

The action of the input phase is controlled by the value of attribute AUTOSCALE_INPUT in the axis node. It can have one of three values.

• AUTOSCALE_OFF turns off autoscaling.
• AUTOSCALE_DATA scans the values in the Data nodes that are attached to the axis to determine the data range. This is the default value.
• AUTOSCALE_WINDOW uses the value of the Window attribute to determine the data range.

Attribute AutoscaleOutput

The value of the AUTOSCALE_OUTPUT attribute can be the bitwise combination of the following values.

• AUTOSCALE_OFF no attributes updated.
• AUTOSCALE_NUMBER updates the value of the Number attribute. This is the number of major tick marks along the axis.
• AUTOSCALE_WINDOW updates the value of the Window attribute. This is the range of numbers displayed along the axis.

The default is AUTOSCALE_NUMBER | AUTOSCALE_WINDOW; both the attributes Number and Window are adjusted.

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