Linear Radial Axis

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

Configuration Options

The axis has configuration properties for ticks, angle lines (line that appear in a radar chart outward from the center), pointLabels (labels around the edge in a radar chart). The following sections define each of the properties in those sections.

NameTypeDescription
angleLinesObjectAngle line configuration. more…
gridLinesObjectGrid line configuration. more…
pointLabelsObjectPoint label configuration. more…
ticksObjectTick configuration. more…

Tick Options

The following options are provided by the linear scale. They are all located in the ticks sub options. The common tick configuration options are supported by this axis.

NameTypeDefaultDescription
backdropColorColor'rgba(255, 255, 255, 0.75)'Color of label backdrops
backdropPaddingXNumber2Horizontal padding of label backdrop.
backdropPaddingYNumber2Vertical padding of label backdrop.
beginAtZeroBooleanfalseif true, scale will include 0 if it is not already included.
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…
maxTicksLimitNumber11Maximum number of ticks and gridlines to show.
precisionNumberif defined and stepSize is not specified, the step size will be rounded to this many decimal places.
stepSizeNumberUser defined fixed step size for the scale. more…
suggestedMaxNumberAdjustment used when calculating the maximum data value. more…
suggestedMinNumberAdjustment used when calculating the minimum data value. more…
showLabelBackdropBooleantrueIf true, draw a background behind the tick labels

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. scale: {
  12. ticks: {
  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. scale: {
  3. ticks: {
  4. max: 5,
  5. min: 0,
  6. stepSize: 0.5
  7. }
  8. }
  9. };

Angle Line Options

The following options are used to configure angled lines that radiate from the center of the chart to the point labels. They can be found in the angleLines sub options. Note that these options only apply if angleLines.display is true.

NameTypeDefaultDescription
displayBooleantrueif true, angle lines are shown
colorColorrgba(0, 0, 0, 0.1)Color of angled lines
lineWidthNumber1Width of angled lines

Point Label Options

The following options are used to configure the point labels that are shown on the perimeter of the scale. They can be found in the pointLabels sub options. Note that these options only apply if pointLabels.display is true.

NameTypeDefaultDescription
callbackFunctionCallback function to transform data labels to point labels. The default implementation simply returns the current string.
fontColorColor/Color[]'#666'Font color for point labels.
fontFamilyString"'Helvetica Neue', 'Helvetica', 'Arial', sans-serif"Font family to use when rendering labels.
fontSizeNumber10font size in pixels
fontStyleString'normal'Font style to use when rendering point labels.