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.

Name Type Description
angleLines Object Angle line configuration. more...
gridLines Object Grid line configuration. more...
pointLabels Object Point label configuration. more...
ticks Object Tick 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.

Name Type Default Description
backdropColor Color 'rgba(255, 255, 255, 0.75)' Color of label backdrops.
backdropPaddingX Number 2 Horizontal padding of label backdrop.
backdropPaddingY Number 2 Vertical padding of label backdrop.
beginAtZero Boolean false if true, scale will include 0 if it is not already included.
min Number User defined minimum number for the scale, overrides minimum value from data. more...
max Number User defined maximum number for the scale, overrides maximum value from data. more...
maxTicksLimit Number 11 Maximum number of ticks and gridlines to show.
precision Number if defined and stepSize is not specified, the step size will be rounded to this many decimal places.
stepSize Number User defined fixed step size for the scale. more...
suggestedMax Number Adjustment used when calculating the maximum data value. more...
suggestedMin Number Adjustment used when calculating the minimum data value. more...
showLabelBackdrop Boolean true If 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.

let minDataValue = Math.min(mostNegativeValue, options.ticks.suggestedMin);
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.

let chart = new Chart(ctx, {
    type: 'radar',
    data: {
        datasets: [{
            label: 'First dataset',
            data: [0, 20, 40, 50]
        }],
        labels: ['January', 'February', 'March', 'April']
    },
    options: {
        scale: {
            ticks: {
                suggestedMin: 50,
                suggestedMax: 100
            }
        }
    }
});

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.

let options = {
    scale: {
        ticks: {
            max: 5,
            min: 0,
            stepSize: 0.5
        }
    }
};

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.

Name Type Default Description
display Boolean true if true, angle lines are shown.
color Color rgba(0, 0, 0, 0.1) Color of angled lines.
lineWidth Number 1 Width of angled lines.
borderDash Number[] [] Length and spacing of dashes on angled lines. See MDN.
borderDashOffset Number 0.0 Offset for line dashes. See MDN.

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.

Name Type Default Description
callback Function Callback function to transform data labels to point labels. The default implementation simply returns the current string.
fontColor Color/Color[] '#666' Font color for point labels.
fontFamily String "'Helvetica Neue', 'Helvetica', 'Arial', sans-serif" Font family to use when rendering labels.
fontSize Number 10 font size in pixels.
fontStyle String 'normal' Font style to use when rendering point labels.

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