Mr_BlackHawk7 Mr_BlackHawk7 - 24 days ago 9
C# Question

Changing a ChartType from Polar to Radar

I asked in a previous question how to set a specific number of rings and sectors for a polar diagram . I now have a button which changes the chart from polar to radar. The problem is the number of segments changes from 24 (correct) to 25 (wrong). I have no idea why.

The code to set the number of rings:

#region chartdesign
Series s = chartleft.Series[0]; // a reference to the default series
ChartArea ca = chartleft.ChartAreas[0]; // a reference to the default chart area
Axis ax = ca.AxisX;
Axis ay = ca.AxisY;
s.ChartType = SeriesChartType.Polar; // set the charttype of the series

ax.Interval = 15;
ay.Interval = 1;

ax.IntervalOffset = 0;
ax.Minimum = 0;
ax.Maximum = 360;

ay.IntervalOffset = 0;
ay.Minimum = 0;
ay.Maximum = 10;
Series s2 = chartright.Series[0]; // a reference to the default series
ChartArea ca2 = chartright.ChartAreas[0]; // a reference to the default chart area
Axis ax2 = ca2.AxisX;
Axis ay2 = ca2.AxisY;
s2.ChartType = SeriesChartType.Polar; // set the charttype of the series

// a few data to test:

s2.Points.AddXY(0, 0);

ax2.Interval = 15;
ay2.Interval = 1;

ax2.IntervalOffset = 0;
ax2.Minimum = 0;
ax2.Maximum = 360;

ay2.IntervalOffset = 0;
ay2.Minimum = 0;
ay2.Maximum = 10;

image: polar
image: Radar


Polar and Radar charts look rather similar, but they really are quite different.

As you saw, in a Polar chart you can influence the number of segments by setting the relevant X-Axis properties.

Most important are the Maximum and the Interval.

Radar is different: It basically works like an indexed chart. This means that all points are sitting at equal distance in a row (or rather a circle) completely ignoring the x-values.

This means that:

  • The number of segments is equal to the number of DataPoints.
  • The values for XAxis.Maximum, -Minimum and -Interval are ignored.
  • No two DataPoints can share the same spot, even if their x-values are the same.

In your example you must have 25 datapoints, probably the first and last being equal. For the Polar chart these will sit at the same spot but for the Radar chart they sit beside each other, hence you see one more segment.

Let me clone the first point and add it to the end:


You can see it even better if you add colors to the first and the last DataPoint:

s.Points.First().Color =  Color.Orange;
s.Points.Last().Color = Color.Red;

Now you can see one colored line segment in the Polar chart but two colored datapoint segments in the Radar chart:

enter image description hereenter image description here

You can also see that I have added 12+1 DataPoints to the Chart. The first and last coincide in the Polar chart but sit beside each other in the Radar chart.