2024-09-30 Share: Polar Graph with ZedGraph in C#

https://stackoverflow.com/questions/11547877/what-library-for-c-sharp-to-use-for-the-graphs-of-a-roundness-meter-software

I was surprised that ZedGraph doesn't support polar graphs out-of-the-box and there are very few examples online. Using this guildline, I created my own polar graph with ZedGraph in C#. I hope that WillKraemer has solved his problem already (4 years passed) and someone else finds my implementation useful.

First is the ZedGraphControl initialization:

        myZg = new ZedGraphControl();
        GraphPane myPane = myZg.GraphPane;

        // Init lists
        RadarPointList dseries1 = new RadarPointList();
        RadarPointList dseries2 = new RadarPointList();

        // Maximize available space in pane
        myPane.Legend.Position = LegendPos.InsideTopLeft;
        myPane.Title.IsVisible = false;
        myPane.XAxis.IsVisible = false;
        myPane.YAxis.IsVisible = false;
        myPane.Border.IsVisible = false;
        myPane.Chart.Border.IsVisible = false;
        myPane.Margin.All = 0;

        // Create concentric grid with 30 degrees spacing & add corresponding labels
        for (double i = 0; i < 36; i+=3.0)
        {
            TextObj gridlbs = new TextObj((i * 10.0).ToString("0°"), (radius + 10.0) * Math.Cos((i * 10.0 * Math.PI) / 180.0), (radius + 10.0) * Math.Sin((i * 10.0 * Math.PI) / 180.0));
            gridlbs.FontSpec.Border.IsVisible = false;
            LineObj gridlns = new LineObj(0, 0, radius * Math.Cos((i * 10.0 * Math.PI) / 180.0), radius * Math.Sin((i * 10.0 * Math.PI) / 180.0));

            myPane.GraphObjList.Add(gridlbs);
            myPane.GraphObjList.Add(gridlns);
        }

        // Draw circular grid, 5 should look okay
        for (double i = (radius / 5.0); i <= radius; i += (radius / 5.0))
        {
            EllipseObj gridcrl = new EllipseObj(-i, i, 2.0 * i, 2.0 * i);
            gridcrl.ZOrder = ZOrder.E_BehindCurves;
            myPane.GraphObjList.Add(gridcrl);
        }

        // Make sure the pane is big enough to fit the labels around the polar plot
        myPane.XAxis.Scale.Min = -(radius + 20.0);
        myPane.XAxis.Scale.Max = (radius + 20.0);
        myPane.YAxis.Scale.Min = -(radius + 20.0);
        myPane.YAxis.Scale.Max = (radius + 20.0);

        _selectedRadius = radius;
        // Keep X & Y axis in the correct ratio to avoid distorting polar circle 
        myZg_Resize((object)"Startup", EventArgs.Empty);
        myZg.Resize += new EventHandler(myZg_Resize);
        myZg.ZoomEvent  += new ZedGraphControl.ZoomEventHandler(myZg_ZoomEvent2);

        // Draw snailly curves (example)
        for (int i = 0; i < 360; i++)
        {
            double r = (double)i/360.0 * radius;
            PointPair pt = new PointPair(PointPair.Missing, r, null);
            dseries1.Add(pt);
            PointPair pt2 = new PointPair(PointPair.Missing, radius - r, null);
            dseries2.Add(pt2);
        }

        // Curves are somple LineItem
        FirstCurve = myPane.AddCurve("Snail", dseries1, Color.Blue, SymbolType.None);
        SecondCurve = myPane.AddCurve("antiSnail", dseries2, Color.Red, SymbolType.None);

        // Rotate the lists to aling with labels
        dseries1.Rotation = 0;
        dseries2.Rotation = 0;

I had to make sure that the graph is not distorted when the form/control resizes, so I added this in the Resize Event:

    protected void myZg_Resize(object sender, EventArgs e)
    {
        GraphPane pane = myZg.GraphPane;
        myZg.AxisChange();
        bool IsXMin = ( pane.Rect.Width < pane.Rect.Height ) ? true : false;
        if (IsXMin)
        {   
            // Scale based on X (width)
            pane.XAxis.Scale.Max = (radius + 20.0); pane.XAxis.Scale.Min = -(radius + 20.0);
            double xPixPerUnit = (double)pane.Chart.Rect.Width / (pane.XAxis.Scale.Max - pane.XAxis.Scale.Min);
            pane.YAxis.Scale.Max = (double)pane.Chart.Rect.Height / xPixPerUnit / 2.0;
            pane.YAxis.Scale.Min = -pane.YAxis.Scale.Max;
            myZg.AxisChange();
        }
        else
        {
            // Scale based on Y (height)
            pane.YAxis.Scale.Max = (radius + 20.0); pane.YAxis.Scale.Min = -(radius + 20.0);
            double yPixPerUnit = (double)pane.Chart.Rect.Height / (pane.YAxis.Scale.Max - pane.YAxis.Scale.Min);
            pane.XAxis.Scale.Max = (double)pane.Chart.Rect.Width / yPixPerUnit / 2.0;
            pane.XAxis.Scale.Min = -pane.XAxis.Scale.Max;
            myZg.AxisChange();
        }
    }

Also, I decided to block the user from any zooming actions:

    protected void myZg_ZoomEvent2(ZedGraphControl sender, ZoomState oldState, ZoomState newState)
    {
        myZg_Resize("zoomevent", EventArgs.Empty);
    }

The output looks like the picture below:

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