Linear Radial Axis

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

The following additional configuration options are provided by the radial linear scale.

Configuration Options

Linear Radial Axis specific options

Namespace: options.scales[scaleId]

NameTypeDefaultDescription
animatebooleantrueWhether to animate scaling the chart from the centre
angleLinesobjectAngle line configuration. more…
beginAtZerobooleanfalseif true, scale will include 0 if it is not already included.
pointLabelsobjectPoint label configuration. more…
startAnglenumber0Starting angle of the scale. In degrees, 0 is at top.

Common options to all axes

Namespace: options.scales[scaleId]

NameTypeDefaultDescription
typestringType of scale being employed. Custom scales can be created and registered with a string key. This allows changing the type of an axis for a chart.
alignToPixelsbooleanfalseAlign pixel values to device pixels.
backgroundColorColorBackground color of the scale area.
displayboolean|stringtrueControls the axis global visibility (visible when true, hidden when false). When display: ‘auto’, the axis is visible only if at least one associated dataset is visible.
gridobjectGrid line configuration. more…
minnumberUser defined minimum number for the scale, overrides minimum value from data. more…
maxnumberUser defined maximum number for the scale, overrides maximum value from data. more…
reversebooleanfalseReverse the scale.
stackedboolean|stringfalseShould the data be stacked. more…
suggestedMaxnumberAdjustment used when calculating the maximum data value. more…
suggestedMinnumberAdjustment used when calculating the minimum data value. more…
ticksobjectTick configuration. more…
weightnumber0The weight used to sort the axis. Higher weights are further away from the chart area.

Tick Configuration

Linear Radial Axis specific tick options

Namespace: options.scales[scaleId].ticks

NameTypeScriptableDefaultDescription
countnumberYesundefinedThe number of ticks to generate. If specified, this overrides the automatic generation.
formatobjectYesThe Intl.NumberFormatLinear Radial Axis - 图1 (opens new window) options used by the default label formatter
maxTicksLimitnumberYes11Maximum number of ticks and gridlines to show.
precisionnumberYesif defined and stepSize is not specified, the step size will be rounded to this many decimal places.
stepSizenumberYesUser defined fixed step size for the scale. more…

Common tick options to all axes

Namespace: options.scales[scaleId].ticks

NameTypeScriptableDefaultDescription
backdropColorColorYes‘rgba(255, 255, 255, 0.75)’Color of label backdrops.
backdropPaddingPaddingYes2Padding of label backdrop.
callbackfunctionReturns the string representation of the tick value as it should be displayed on the chart. See callback.
displaybooleantrueIf true, show tick labels.
colorColorYesChart.defaults.colorColor of ticks.
fontFontYesChart.defaults.fontSee Fonts
majorobject{}Major ticks configuration.
paddingnumber3Sets the offset of the tick labels from the axis
showLabelBackdropbooleanYestrue for radial scale, false otherwiseIf true, draw a background behind the tick labels.
textStrokeColorColorYes``The color of the stroke around the text.
textStrokeWidthnumberYes0Stroke width around the text.
znumber0z-index of tick layer. Useful when ticks are drawn on chart area. Values <= 0 are drawn under datasets, > 0 on top.

The scriptable context is described in Options section.

Axis Range Settings

Given the number of axis range settings, it is important to understand how they all interact with each other.

The suggestedMax and suggestedMin settings only change the data values that are used to scale the axis. These are useful for extending the range of the axis while maintaining the auto fit behaviour.

  1. let minDataValue = Math.min(mostNegativeValue, options.ticks.suggestedMin);
  2. let maxDataValue = Math.max(mostPositiveValue, options.ticks.suggestedMax);

In this example, the largest positive value is 50, but the data maximum is expanded out to 100. However, because the lowest data value is below the suggestedMin setting, it is ignored.

  1. let chart = new Chart(ctx, {
  2. type: 'radar',
  3. data: {
  4. datasets: [{
  5. label: 'First dataset',
  6. data: [0, 20, 40, 50]
  7. }],
  8. labels: ['January', 'February', 'March', 'April']
  9. },
  10. options: {
  11. scales: {
  12. r: {
  13. suggestedMin: 50,
  14. suggestedMax: 100
  15. }
  16. }
  17. }
  18. });

In contrast to the suggested* settings, the min and max settings set explicit ends to the axes. When these are set, some data points may not be visible.

Step Size

If set, the scale ticks will be enumerated by multiple of stepSize, having one tick per increment. If not set, the ticks are labeled automatically using the nice numbers algorithm.

This example sets up a chart with a y axis that creates ticks at 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5.

  1. let options = {
  2. scales: {
  3. r: {
  4. max: 5,
  5. min: 0,
  6. ticks: {
  7. stepSize: 0.5
  8. }
  9. }
  10. }
  11. };

Angle Line Options

The following options are used to configure angled lines that radiate from the center of the chart to the point labels. Namespace: options.scales[scaleId].angleLines

NameTypeScriptableDefaultDescription
displaybooleantrueif true, angle lines are shown.
colorColorYesChart.defaults.borderColorColor of angled lines.
lineWidthnumberYes1Width of angled lines.
borderDashnumber[]Yes1[]Length and spacing of dashes on angled lines. See MDNLinear Radial Axis - 图2 (opens new window).
borderDashOffsetnumberYes0.0Offset for line dashes. See MDNLinear Radial Axis - 图3 (opens new window).
  1. the borderDash setting only accepts a static value or a function. Passing an array of arrays is not supported.

The scriptable context is described in Options section.

Point Label Options

The following options are used to configure the point labels that are shown on the perimeter of the scale. Namespace: options.scales[scaleId].pointLabels

NameTypeScriptableDefaultDescription
backdropColorColortrueundefinedBackground color of the point label.
backdropPaddingPadding2Padding of label backdrop.
displaybooleantrueif true, point labels are shown.
callbackfunctionCallback function to transform data labels to point labels. The default implementation simply returns the current string.
colorColorYesChart.defaults.colorColor of label.
fontFontYesChart.defaults.fontSee Fonts
paddingnumberYes5Padding between chart and point labels.

The scriptable context is described in Options section.

Internal data format

Internally, the linear radial scale uses numeric data