Question

我想绘制正弦波，但我的应用程序生成一条扁平线。当我使用来自jchartfree示例的随机系列时，一切正常。我还使用调试器来检查值是否良好。值不同于零

public void createDataset() {
    XYSeriesCollection dataset = new XYSeriesCollection();
    XYSeries series1 = new XYSeries("Object 1");

    double A = 1;                       
    double T = 1;                       
    double Fs = 10;                   
    double f = 200;                     
    int rozmiar = (int) (T*Fs);

    double[] x = new double[rozmiar];

   for (int i = 0; i < rozmiar; i++)
   {
        x[i] = A * Math.sin(2 * Math.PI * f * i / Fs);
        series1.add(i, x[i]);
   }

    dataset.addSeries(series1);

    data = dataset;
}
//...
public void createChartPanel() {
    //pWykres = new JPanel();
    //if(java.util.Arrays.asList(getComponents()).contains(pWykres)){
        //getContentPane().remove(pWykres);
    //}
    if(pWykres != null){
        pWykres.removeAll();
        pWykres.revalidate();
    }

    String chartTitle = "Objects Movement Chart";
    String xAxisLabel = "X";
    String yAxisLabel = "Y";

    JFreeChart chart = ChartFactory.createXYLineChart(chartTitle,
            xAxisLabel, yAxisLabel, dataset);

    customizeChart(chart);

    pWykres = new ChartPanel(chart);
    getContentPane().add(pWykres, BorderLayout.CENTER);
    setSize(620, 460);
    //validate();
    pWykres.repaint();
}
//endregion
//...    
//region 
private void customizeChart(JFreeChart chart) {
    XYPlot plot = chart.getXYPlot();
    XYSplineRenderer renderer;
            renderer = new XYSplineRenderer();
            renderer.setSeriesShapesVisible(0, false);

    // sets paint color for each series
    renderer.setSeriesPaint(0, Color.RED);

    // sets thickness for series (using strokes)
    renderer.setSeriesStroke(0, new BasicStroke(1.0f));

    // sets paint color for plot outlines
    //plot.setOutlinePaint(Color.BLUE);
    //plot.setOutlineStroke(new BasicStroke(2.0f));

    // sets renderer for lines
    plot.setRenderer(renderer);

    // sets plot background
    plot.setBackgroundPaint(Color.WHITE);

    // sets paint color for the grid lines
    plot.setRangeGridlinesVisible(true);
    plot.setRangeGridlinePaint(Color.BLACK);

    plot.setDomainGridlinesVisible(true);
    plot.setDomainGridlinePaint(Color.BLACK);
}

Answer 1

你正在使用的值的正弦值始终是2 * PI的整数倍，因此所有这些值都将（大约）为零，因此除非缩放显示这些值，否则图表最终会显得平坦微小的值（只是浮点错误）。

x[i] = A * Math.sin(2 * Math.PI * f * i / Fs);

其中A = 1且f/Fs = 20且i为整数

例如：

Math.sin(0)             // 0.0
Math.sin(2 * Math.PI)   // -2.4492935982947064E-16  (approximately zero)
Math.sin(4 * Math.PI)   // -4.898587196589413E-16   (approximately zero)

要查看正弦波的特征形状，您需要以更小的增量更改sin函数的输入，例如pi / 10或更低。

扁线代替波

1 个答案: