Qt图表，如何根据其值来缩放轴

Question

我有大约600对x和y值需要绘制。它们以double形式从CSV文件中读取。

void ChartView::getData4Series()
{
QFile file(QCoreApplication::applicationDirPath() + "/../saveData/" + m_videoPath + "/" + "SaveDisplace.csv");
if (!file.open(QIODevice::ReadOnly))
{
    QMessageBox::information(0, "error", file.errorString());
}
QTextStream in(&file);
QString line;
QStringList fields;

QtCharts::QScatterSeries* series = new QtCharts::QScatterSeries;
m_seriesTy->clear();
m_seriesTz->clear();
bool checkforChar ;
while (!in.atEnd())
{
    line = in.readLine();
    fields = line.split(";");
    fields[2].toDouble(&checkforChar);
    if (checkforChar)
    {
        if (fields[2].toDouble() <= 100.0 && fields[2].toDouble() >= -5000.0)
        {
            if (fields[6].toDouble() > -100000.0)
            {
                m_seriesTy->append(fields[2].toDouble(), (fields[3].toDouble() - fields[6].toDouble()));
                m_seriesTz->append(fields[2].toDouble(), (fields[4].toDouble() - fields[7].toDouble()));
            }
        }
    }

}
file.close();
}

我通过设置轴、给出限制并添加一条额外的线（仅有2个值对）作为参考，来设置图表。

void ChartView::setZErrorCharts(QtCharts::QScatterSeries* series)
{
series->setMarkerSize(8);
QtCharts::QValueAxis *xAxis = new QtCharts::QValueAxis;
QtCharts::QValueAxis *yAxis = new QtCharts::QValueAxis;
xAxis->setRange(-5000, 0);
yAxis->setRange(-500, 500);

QtCharts::QLineSeries* lineSeries = new QtCharts::QLineSeries;
lineSeries->append(qreal(0), qreal(0));
lineSeries->append(qreal(-5000), qreal(0));

m_chartTzError = new QtCharts::QChart();

m_chartTzError->setAxisX(xAxis);
m_chartTzError->setAxisY(yAxis);
m_chartTzError->setTitle("tz error ");

m_chartTzError->legend()->hide();
m_chartTzError->addSeries(series);
m_chartTzError->addSeries(lineSeries);  

}

我所看到的是轴的值不适合实际绘制的值。我还将值作为标签绘制，它们与x和y轴的值也不同。轴的缩放如何安排？我尝试通过改变顺序，在添加数据系列之前设置轴范围或反之亦然。由红圈标记的值应该接近于0，但实际上约为-200。有什么解决办法吗？Qt参考似乎没有帮助。

- Maik

Answer 1

我曾经遇到同样的问题，解决方法如下：

1. You create the axes which you need first. For example:

   QLogValueAxis *axisX = new QLogValueAxis();  
   axisX->setTitleText("Frequency [Hz]");  
   axisX->setRange(200, 8000);  
   axisX->setMinorGridLineVisible(true);  
   axisX->setMinorTickCount(10);  
   chart->addAxis(axisX, Qt::AlignBottom);  
   
   QValueAxis *axisY = new QValueAxis();  
   axisY->setRange(20, 150);  
   axisY->setTitleText("dB");  
   chart->addAxis(axisY, Qt::AlignLeft);  
   

2. Then, you create your series':
   QLineSeries *series = new QLineSeries(chart);
   series->append(x,y);

3. Add the series to your chart:
   chart->addSeries(series);

4. Finally, attach the right axis to the series:
   series->attachAxis(axisX);
   series->attachAxis(axisY);

现在当你绘制它时：

ui->chart_view->setChart(chart);  

一切都应该按照正确的比例来展示。
我认为关键的步骤是在将系列添加到图表时附加正确的对应轴。

- Ferhat Özdogan