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  Real time data and smooth scrolling
Posted by Todd on Jul-20-2011 01:56
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I am trying to create a real time scrolling window, similar to the example in the NetWinCharts sample.  Instead of dates for the X axis, I'm using doubles.

The problem is, my graph is very jumpy.  The X axis wants to round to the nearest 5 or 10 or 20 mark, which causes it to lurch as it adds data points.

The sample provided is very smooth and the graph lines are always flush with the edges of the graph.  I can't figure out what is different in my code that is causing this.

Any help would be appreciated.  The code is included below.

Todd

    public partial class Form1 : Form
    {
        Random r = new Random();

        public Form1()
        {
            InitializeComponent();

            InitializeRealTimeData();
            DrawChart();
            timer1.Enabled = true;
        }

        public const double point_count = 100;
        public double start_x = -point_count;
        public double next_y = 50.0;
        List<double> data = new List<double>();

        private void InitializeRealTimeData()
        {
            data.Clear();
            for (int i = 0; i < point_count; i++)
                data.Add(double.NaN);
        }

        private void UpdateRealtimeData()
        {
            data.Add(next_y);
            next_y += (r.Next(10) / 10.0 - 0.45);

            if (data.Count > point_count)
            {
                data.RemoveAt(0);
                start_x++;
            }
        }

        private void DrawChart()
        {
            Size new_control_size = winChartViewer1.Size;

            int chart_height = new_control_size.Height;
            int chart_width = new_control_size.Width;

            ChartDirector.XYChart chart = new ChartDirector.XYChart(chart_width, chart_height);

            chart.setPlotArea(45, 35, chart_width - 80, chart_height - 70, -1, -1, -1, -1, -1);
            chart.setClipping();

            chart.xAxis().setLinearScale(start_x, start_x + point_count);

            ChartDirector.LineLayer layer = chart.addLineLayer2();

            layer.addDataSet(data.ToArray(), 0x0000ff, "Apples");

            List<double> xData = new List<double>();
            for (int i = 0; i < data.Count; i++)
                xData.Add(i + (int)start_x);

            layer.setXData(xData.ToArray());

            winChartViewer1.Chart = chart;
        }

        private void timer1_Tick(object sender, EventArgs e)
        {
            UpdateRealtimeData();
            DrawChart();
        }

        private void startStop_Click(object sender, EventArgs e)
        {
            timer1.Enabled = !timer1.Enabled;
        }
    }

  Re: Real time data and smooth scrolling
Posted by Peter Kwan on Jul-20-2011 03:44
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Hi Todd,

The issue you see is probably caused by axis rounding. By default, ChartDirector will make sure the axis starts and ends at a "tick" position. (For example, instead of an axis range of 83.4498 to 115.982, ChartDirector may choose 80 to 120, assuming there is a tick every 10 units.)

If the above is the cause of the problem, disabling axis rounding should solve the problem:

c.xAxis().setRounding(false, false);

Hope this can help.

Regards
Peter Kwan