Radial Axes

Radial axes are used specifically for the radar and polar area chart types. These axes overlay the chart area, rather than being positioned on one of the edges.

Radial axes could be only

• linear, is use to chart numerical data. As the name suggests, linear interpolation is used to determine where a value lies in relation the center of the axis.

The radial axis is use to chart numerical data.

Here is an example how to create a radial axis:

// creates a radial axis with default scale id "r" and default kind "r" 
RadialAxis axis = new RadialAxis(chart);

// adds axes to chart configuration
chart.getOptions().setAxes(axis);

The axis has configuration properties for ticks, angle lines (line that appear in a radar chart outward from the center), point labels (labels around the edge in a radar chart):

Options

The radial linear axis allows to define a number of properties, used to display the data.

// creates a radial axis 
RadialAxis axis = new RadialAxis(chart);
// sets and gets the max value
axis.setMax(100);

double max = axis.getMax();

The following are the attributes that you can set:

Name	Type	Description
alignToPixels	boolean	Align pixel values to device pixels.
animate	boolean	If true, animate scaling the chart from the center.
backgroundColor	String - IsColor	The background color of scale area.
beginAtZero	boolean	If true, scale will include 0 if it is not already included.
display	boolean - Display	If Display.TRUE, the axis is shown.
max	double	User defined maximum number for the scale, overrides maximum value from data.
min	double	User defined minimum number for the scale, overrides minimum value from data.
reverse	boolean	Reverses order of tick labels.
startAngle	double	0
suggestedMax	double	Adjustment used when calculating the maximum data value.
suggestedMin	double	Adjustment used when calculating the minimum data value.
weight	int	The weight used to sort the axis. Higher weights are further away from the chart area.

Ticks

The radial linear axis provides the following options for configuring tick marks.

// creates a radial axis 
RadialAxis axis = new RadialAxis(chart);
// sets and gets the max value
axis.getTicks().setColor(HtmlColor.RED);

IsColor color = axis.gteTicks().getColor();

The following are the attributes that you can set:

Name	Type	Scriptable	Description
backdropColor	String - IsColor	Yes	Color of label backdrops.
backdropPadding	Padding		The padding of tick backdrop. See padding documentation for more details.
color	String - IsColor	Yes	Color of ticks.
count	int	[Yes](#scriptable	The number of ticks to generate. If specified, this overrides the automatic generation.
display	boolean	-	If true, the tick marks are shown.
font	IsFont	Yes	Font of ticks. See Font.
maxTicksLimit	int	[Yes](#scriptable	Maximum number of ticks and gridlines to show.
numberFormat	NumberFormatOptions	Yes	The number format options used by the default label formatter. See INTL number format documentation.
padding	int	-	The padding between the tick label and the axis.
precision	int	[Yes](#scriptable	If defined and stepSize is not specified, the step size will be rounded to this many decimal places.
sampleSize	int	-	The number of ticks to examine when deciding how many labels will fit. Setting a smaller value will be faster, but may be less accurate when there is large variability in label length.
showLabelBackdrop	boolean	Yes	If true, draw a background behind the tick labels
stepSize	double	Yes	User defined fixed step size for the scale.
textStrokeColor	String - IsColor	Yes	The color of the stroke around the text.
textStrokeWidth	int	Yes	Stroke width around the text.
z	int	-	z-index of tick layer. Useful when ticks are drawn on chart area. Values less than or equals to 0 are drawn under data sets, greater than 0 on top.

The further customization of ticks, a callback is provided.

See [padding documentation](../configuration/Commons#padding) for more details.

Scriptable

Scriptable options at ticks level accept a callback which is called for each of the underlying data values. See more details in Configuring charts section.

All scriptable options callbacks will get a ScaleContext instance.

// creates a radial axis 
RadialAxis axis = new RadialAxis(chart);
// sets the option by a callback 
axis.getTicks().setColor(new ColorCallback<ScaleContext>(){

   @Override
   public IsColor invoke(ScaleContext context){
      // logic
      return color;
   }
});

The following options can be set by a callback:

Name	Callback	Returned types
backdropColor	ColorCallback<ScaleContext>	String - IsColor
color	ColorCallback<ScaleContext>	String - IsColor
count	CountCallback	int
font	FontCallback<ScaleContext>	FontItem
maxTicksLimit	MaxTicksLimitCallback	int
numberFormat	NumberFormatCallback	NumberFormatItem
precision	PrecisionCallback	int
showLabelBackdrop	ShowLabelBackdropCallback	boolean
stepSize	StepSizeCallback	double
textStrokeColor	ColorCallback<ScaleContext>	String - IsColor
textStrokeWidth	WidthCallback<ScaleContext>	int

Callback

It is also common to want to change the tick marks to include information about the data type. For example, adding a dollar sign ('$'). To do this, you need to implement a ticks callback in the axis configuration.

To apply a custom callback, you can set a TickCallback instance to the axis options, as following:

axis.getTicks().setCallback(new TickCallback(){

   /**
    * Changes the tick marks to include information about the data type.
    * 
    * @param axis axis instance where this callback as been defined
    * @param value value of tick
    * @param index index of tick
    * @param values list of all tick values
    * @return the tick to apply or if the callback returns null the associated grid line will be hidden.
    */
   public String onCallback(Axis axis, double value, int index, List<Double> values){
      // add $
      return "$" + value;
   }
         
});

See INTL number format documentation if you want to use a number formatter, provided out-of-the-box.

NoSelectedDatasetTicksCallback callback

Charba provides a common implementation for tick callback to set the decimal digits of ticks in case of all data sets are hidden, to avoid the annoying standard format of doubles.

To apply the callback, you can set an instance to the axis options, as following:

// creates a radial axis 
RadialAxis axis = new RadialAxis(chart);
// sets the option by a callback 
axis.getTicks().setCallback(new NoSelectedDatasetTicksCallback());

The default decimal precision is 2. A custom precision can be set by the constructor of callback, as following:

// creates a radial axis 
RadialAxis axis = new RadialAxis(chart);
// sets the option by a callback 
// 3 decimal digits 
axis.getTicks().setCallback(new NoSelectedDatasetTicksCallback(3));