Polar Axis

A polar axis can be added to the plot, then other plot types (marker, line, scatter, etc.) can be placed on top of it using its helper methods to translate polar coordinates to Cartesian units.

PolarAxis.cs

ScottPlot.Plot myPlot = new();

// add a polar axis to the plot
var polarAxis = myPlot.Add.PolarAxis();

IColormap colormap = new ScottPlot.Colormaps.Turbo();
foreach (double degrees in ScottPlot.Generate.Range(0, 360, 10))
{
    // use the polar axis to get X/Y coordinates given a position in polar space
    double radius = degrees / 360.0;
    Coordinates pt = polarAxis.GetCoordinates(radius, degrees);

    // place markers or other plot types using X/Y coordinates like normal
    var marker = myPlot.Add.Marker(pt);
    marker.Color = colormap.GetColor(radius);
}

myPlot.SavePng("demo.png", 400, 300);

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Polar Axis Rotation

A polar axis may be rotated to define the angle of the 0 degree spoke.

PolarAxis.cs

ScottPlot.Plot myPlot = new();

var polarAxis = myPlot.Add.PolarAxis();
polarAxis.Rotation = Angle.FromDegrees(90); // default direction is counter-clockwise

IColormap colormap = new ScottPlot.Colormaps.Turbo();
foreach (double degrees in ScottPlot.Generate.Range(0, 360, 10))
{
    double radius = degrees / 360.0;
    Coordinates pt = polarAxis.GetCoordinates(radius, degrees);

    var marker = myPlot.Add.Marker(pt);
    marker.Color = colormap.GetColor(radius);
}

myPlot.SavePng("demo.png", 400, 300);

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Clockwise Polar Axis

Clockwise polar plots are common for representing spatial orientation.

PolarAxis.cs

ScottPlot.Plot myPlot = new();

var polarAxis = myPlot.Add.PolarAxis();
polarAxis.Clockwise = true;
polarAxis.Rotation = Angle.FromDegrees(-90); // direction will be counter-clockwise

IColormap colormap = new ScottPlot.Colormaps.Turbo();
foreach (double degrees in ScottPlot.Generate.Range(0, 360, 10))
{
    double fraction = degrees / 360.0;
    Coordinates pt = polarAxis.GetCoordinates(fraction, degrees);
    var marker = myPlot.Add.Marker(pt);
    marker.Color = colormap.GetColor(fraction);
}

myPlot.SavePng("demo.png", 400, 300);

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Polar Axis with Arrows

Arrows can be placed on a polar coordinate system with their base at the center and their tips used to indicate points in polar space. The Phaser plot type uses this strategy to display collections of similarly styled arrows.

PolarAxis.cs

ScottPlot.Plot myPlot = new();

PolarCoordinates[] points = [
    new(10, Angle.FromDegrees(15)),
    new(20, Angle.FromDegrees(120)),
    new(30, Angle.FromDegrees(240)),
];

var polarAxis = myPlot.Add.PolarAxis(radius: 30);
polarAxis.Circles.ForEach(x => x.LinePattern = LinePattern.Dotted);
polarAxis.Spokes.ForEach(x => x.LinePattern = LinePattern.Dotted);

IPalette palette = new ScottPlot.Palettes.Category10();
Coordinates center = polarAxis.GetCoordinates(0, 0);
for (int i = 0; i < points.Length; i++)
{
    Coordinates tip = polarAxis.GetCoordinates(points[i]);
    var arrow = myPlot.Add.Arrow(center, tip);
    arrow.ArrowLineWidth = 0;
    arrow.ArrowFillColor = palette.GetColor(i).WithAlpha(.7);
}

myPlot.SavePng("demo.png", 400, 300);

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Polar Axis Styling

The lines of polar axes may be extensively styled. Polar axes have radial spokes (straight lines that extend from the origin to the maximum radius) and circular axis lines (concentric circles centered at the origin).

PolarAxis.cs

ScottPlot.Plot myPlot = new();

var polarAxis = myPlot.Add.PolarAxis();

// style the spokes (straight lines extending from the center to mark rotations)
var radialPalette = new ScottPlot.Palettes.Category10();
for (int i = 0; i < polarAxis.Spokes.Count; i++)
{
    polarAxis.Spokes[i].LineColor = radialPalette.GetColor(i).WithAlpha(.5);
    polarAxis.Spokes[i].LineWidth = 4;
    polarAxis.Spokes[i].LabelStyle.ForeColor = radialPalette.GetColor(i);
    polarAxis.Spokes[i].LabelStyle.FontSize = 16;
    polarAxis.Spokes[i].LabelStyle.Bold = true;
}

// style the circles (concentric circles marking radius positions)
var circularColormap = new ScottPlot.Colormaps.Rain();
for (int i = 0; i < polarAxis.Circles.Count; i++)
{
    double fraction = (double)i / (polarAxis.Circles.Count - 1);
    polarAxis.Circles[i].LineColor = circularColormap.GetColor(fraction).WithAlpha(.5);
    polarAxis.Circles[i].LineWidth = 2;
    polarAxis.Circles[i].LinePattern = LinePattern.Dashed;
}

myPlot.SavePng("demo.png", 400, 300);

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Polar Axis Background

The background style of polar axes may be customized

PolarAxis.cs

ScottPlot.Plot myPlot = new();

var polarAxis = myPlot.Add.PolarAxis();
polarAxis.FillColor = Colors.Blue.WithAlpha(.2);

myPlot.SavePng("demo.png", 400, 300);

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Polar Axis Spoke Length

The length of spokes may be customized. Spoke length is expressed as a fraction of the polar axis radius.

PolarAxis.cs

ScottPlot.Plot myPlot = new();

myPlot.Add.PolarAxis(spokeLength: 1.3);

myPlot.SavePng("demo.png", 400, 300);

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Polar Axis Spoke Labels

Polar axis spokes may be individually labeled.

PolarAxis.cs

ScottPlot.Plot myPlot = new();

var polarAxis = myPlot.Add.PolarAxis();

string[] labels = { "alpha", "beta", "gamma", "delta", "epsilon" };
polarAxis.SetSpokes(labels, 1.1);

myPlot.SavePng("demo.png", 400, 300);

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Polar Axis Tick Labels

Polar axis ticks are marked by circles which may be individually labeled.

PolarAxis.cs

ScottPlot.Plot myPlot = new();

var polarAxis = myPlot.Add.PolarAxis();
polarAxis.Rotation = Angle.FromDegrees(-90);

double[] ticksPositions = { 5, 10, 15, 20 };
string[] tickLabels = { "A", "B", "C", "D" };
polarAxis.SetCircles(ticksPositions, tickLabels);

polarAxis.SetSpokes(count: 5, length: 22, degreeLabels: false);

myPlot.SavePng("demo.png", 400, 300);

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Polar Axis Line Customization

The angle and length of spokes and position of circles can be manually defined. Each spoke and circle may also be individually styled.

PolarAxis.cs

ScottPlot.Plot myPlot = new();

var polarAxis = myPlot.Add.PolarAxis();

// define spoke angle and length
polarAxis.Spokes.Clear();
polarAxis.Spokes.Add(new(Angle.FromDegrees(0), 0.5));
polarAxis.Spokes.Add(new(Angle.FromDegrees(45), 0.75));
polarAxis.Spokes.Add(new(Angle.FromDegrees(90), 1.0));

// define circle radius
polarAxis.Circles.Clear();
polarAxis.Circles.Add(new(0.5));
polarAxis.Circles.Add(new(0.75));
polarAxis.Circles.Add(new(1.0));

// style individual spokes and circles
ScottPlot.Palettes.Category10 pal = new();
for (int i = 0; i < 3; i++)
{
    polarAxis.Circles[i].LineColor = pal.GetColor(i).WithAlpha(.5);
    polarAxis.Spokes[i].LineColor = pal.GetColor(i).WithAlpha(.5);

    polarAxis.Circles[i].LineWidth = 2 + i * 2;
    polarAxis.Spokes[i].LineWidth = 2 + i * 2;
}

myPlot.SavePng("demo.png", 400, 300);

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Polar Radar Plot

Combining a polar axis with polygons is an alternative strategy for building radar plots.

PolarAxis.cs

ScottPlot.Plot myPlot = new();

var polarAxis = myPlot.Add.PolarAxis();
polarAxis.Clockwise = true;
polarAxis.Rotation = Angle.FromDegrees(-90);

// add labeled spokes
string[] labels = { "Alpha", "Beta", "Gamma", "Delta", "Epsilon" };
polarAxis.SetSpokes(labels, length: 5.5);

// add defined ticks
double[] ticks = { 1, 2, 3, 4, 5 };
polarAxis.SetCircles(ticks);

// convert radar values to coordinates
double[] values1 = { 5, 4, 3, 2, 3 };
double[] values2 = { 2, 3, 2, 4, 2 };
Coordinates[] cs1 = polarAxis.GetCoordinates(values1);
Coordinates[] cs2 = polarAxis.GetCoordinates(values2);

// add polygons for each dataset
var poly1 = myPlot.Add.Polygon(cs1);
poly1.FillColor = Colors.Green.WithAlpha(.5);
poly1.LineColor = Colors.Black;

var poly2 = myPlot.Add.Polygon(cs2);
poly2.FillColor = Colors.Blue.WithAlpha(.5);
poly2.LineColor = Colors.Black;

myPlot.SavePng("demo.png", 400, 300);

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Polar Spoke Label Padding

Modifies the padding of labels on polar spokes.

PolarAxis.cs

ScottPlot.Plot myPlot = new();

var polarAxis = myPlot.Add.PolarAxis();
polarAxis.SetSpokes(4, 1);

for (int i = 0; i < polarAxis.Spokes.Count; i++)
{
    polarAxis.Spokes[i].LineWidth = 4;
    polarAxis.Spokes[i].LabelStyle.FontSize = 16;
    polarAxis.Spokes[i].LabelPaddingFraction = 0.2 * i;
    polarAxis.Spokes[i].LabelText = $"{polarAxis.Spokes[i].LabelLength}";
}

myPlot.SavePng("demo.png", 400, 300);

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Polar Axis with Lines

This is an example of a polar axis with lines instead of points

PolarAxis.cs

ScottPlot.Plot myPlot = new();

// add a polar axis to the plot
var polarAxis = myPlot.Add.PolarAxis(radius: 100);

IColormap colormap = new ScottPlot.Colormaps.Turbo();
Coordinates? previousPt = null;

foreach (double fraction in ScottPlot.Generate.Range(0, 1, 0.02))
{
    // use the polar axis to get X/Y coordinates given a position in polar space
    double radius = 100 * fraction;
    double degrees = 360 * fraction;
    Coordinates pt = polarAxis.GetCoordinates(radius, degrees);

    if (previousPt != null)
    {
        ScottPlot.Plottables.LinePlot lp = myPlot.Add.Line(previousPt.Value.X, previousPt.Value.Y, pt.X, pt.Y);
        lp.LineWidth = 5;
        lp.Color = Colors.Red;
        previousPt = pt;
    }
    else
    {
        previousPt = pt;
    }
}

myPlot.SavePng("demo.png", 400, 300);

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