Zoom in downsampling chart

问题

I use a .NET Winform version teechart 4.1.2012.1032.

I modified the sample that you supplied. "Extended\Reducing number of points\DownSampling Additions" But When I zoom in chart, fastline's marks count is not 100 , downSampling.DisplayedPointCount. How can I resolve it?

  private void InitializeChart()
  {
        this.cursorTool1 = new Steema.TeeChart.Tools.CursorTool();//
        this.tChart1.Tools.Add(this.cursorTool1);//
        this.cursorTool1.FollowMouse = true;//
        this.cursorTool1.Style = Steema.TeeChart.Tools.CursorToolStyles.Vertical;//
        this.cursorTool1.Change += new Steema.TeeChart.Tools.CursorChangeEventHandler(this.cursorTool1_Change);//

        CreateArrays();
        tChart1.Aspect.View3D = false;
        tChart1.Zoom.Direction = ZoomDirections.Both;//.Horizontal;//
        tChart1.Series.Add(points = new Steema.TeeChart.Styles.Points());
        tChart1.Series.Add(fastLine = new Steema.TeeChart.Styles.FastLine());

        downSampling = new Steema.TeeChart.Functions.DownSampling(tChart1.Chart);
        points.Add(xValues, yValues);
        points.Active = false;

        downSampling.DisplayedPointCount = 100;
        downSampling.Method = Steema.TeeChart.Functions.DownSamplingMethod.MinMaxFirstLast;// Null;
        fastLine.TreatNulls = Steema.TeeChart.Styles.TreatNullsStyle.DoNotPaint;
        fastLine.DataSource = points;
        fastLine.Function = downSampling;

        this.tChart1.Axes.Custom.Add(new Steema.TeeChart.Axis(this.tChart1.Chart));//
        this.tChart1[1].CustomVertAxis = this.tChart1.Axes.Custom[0];//
        this.tChart1[0].CustomVertAxis = this.tChart1.Axes.Custom[0];//

        this.fastLine.Marks.Visible = true;//
    }

    private void CreateArrays()
    {
        int length = 2600000;

        xValues = new Nullable<double>[length];
        yValues = new Nullable<double>[length];

        Random rnd = new Random();
        for (int i = 0; i < length; i++)
        {
          xValues[i] = i;
          yValues[i] = i;
        }
    }

    private void tChart1_Zoomed(object sender, EventArgs e)
    {
        tChart1[1].CheckDataSource(); //series 1 is the function series
    }

回答1:

The DisplayedPointCount specifies how many points the DownSampling function should paint and displays this number as a maximum number of points. As I explained here, you may need to combine it with Tolerance property to get the results you expect. So, you could do something like this:

  public partial class Form1 : Form
  {
    public Form1()
    {
      InitializeComponent();
      InitializeChart();
    }

    private void InitializeChart()
    {
      //tChart1.Dock = DockStyle.Fill;
      tChart1.Aspect.View3D = false;
      tChart1.Zoomed += tChart1_Zoomed;

      Steema.TeeChart.Styles.Points points1 = new Steema.TeeChart.Styles.Points(tChart1.Chart);

      Random y = new Random();
      for (int i = 0; i < 10000; i++)
      {
        points1.Add(DateTime.Now.AddHours(i), y.Next());
      }

      points1.XValues.DateTime = true;
      points1.Pointer.HorizSize = 1;
      points1.Pointer.VertSize = 1;

      Steema.TeeChart.Functions.DownSampling downSampling1 = new Steema.TeeChart.Functions.DownSampling(tChart1.Chart);
      downSampling1.Method = Steema.TeeChart.Functions.DownSamplingMethod.Average;
      downSampling1.Tolerance = 100;
      downSampling1.DisplayedPointCount = Convert.ToInt32(downSampling1.Tolerance * 4);

      Steema.TeeChart.Styles.Line line1 = new Steema.TeeChart.Styles.Line(tChart1.Chart);
      line1.Function = downSampling1;
      line1.DataSource = points1;
      line1.Marks.Visible = true;
      line1.Marks.Style = MarksStyles.PointIndex;

      UpdateTitle();
    }

    void tChart1_Zoomed(object sender, EventArgs e)
    {
      tChart1[1].CheckDataSource();
      UpdateTitle();
    }

    private void UpdateTitle()
    {
      tChart1.Header.Text = (tChart1[1].Function as Steema.TeeChart.Functions.DownSampling).DisplayedPointCount.ToString();
    }
  }

来源：https://stackoverflow.com/questions/26054996/zoom-in-downsampling-chart

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