c++qtqt5qchartqchartview

Qt: QPolarChart with categorial angular axis


I would like to replace the degrees of an angular axis in a QPolarChart with some text like shown in the attached figure (e.g instead of 90.0 -> "Cat 1"). I tried QCategoryAxis but in this case the categories appeared between the axis (e.g between 90 and 180 degree).

Now I am using the following code in order to create the polar chart:

QPolarChart *chart = new QPolarChart();

QValueAxis *angularAxis = new QValueAxis();
angularAxis->setRange(0, 360);

QLineSeries *series1 = new QLineSeries();
series1->append(0, 60);
series1->append(90, -60);
series1->append(180, 50);
series1->append(270, 62);
series1->append(360, 60);

QLineSeries *series2 = new QLineSeries();
series2->append(0, 0);
series2->append(90, 0);
series2->append(180, 0);
series2->append(270, 0);
series2->append(360, 0);

chart->addSeries(series1);
chart->addSeries(series2);
chart->addAxis(angularAxis, QPolarChart::PolarOrientationAngular);

ValueAxis *radialAxis = new QValueAxis();
radialAxis->setTickCount(9);
radialAxis->setLabelFormat("%d");
chart->addAxis(radialAxis, QPolarChart::PolarOrientationRadial);

series1->attachAxis(radialAxis);
series1->attachAxis(angularAxis);
series2->attachAxis(radialAxis);
series2->attachAxis(angularAxis);

radialAxis->setRange(-100, 100);

QChartView *chartView = new QChartView();
chartView->setChart(chart);
chartView->setRenderHint(QPainter::Antialiasing);

ui->mainPlot->addWidget(chartView);

PolarPlot


Solution

  • The solution is to use QCategoryAxis but with the labelsPosition in QCategoryAxis::AxisLabelsPositionOnValue.

    #include <QApplication>
    
    #include <QtCharts>
    using namespace QtCharts;
    
    int main(int argc, char *argv[])
    {
        QApplication a(argc, argv);
        QPolarChart *chart = new QPolarChart();
    
        QCategoryAxis *angularAxis = new QCategoryAxis;
        angularAxis->setLabelsPosition(QCategoryAxis::AxisLabelsPositionOnValue);
        angularAxis->setRange(0, 360);
        angularAxis->append("Cat 1", 90);
    
        QLineSeries *series1 = new QLineSeries();
        *series1 << QPointF(0, 60) << QPointF(90, -60) << QPointF(180, 50) << QPointF(270, 62) << QPointF(360, 60);
    
        QLineSeries *series2 = new QLineSeries();
        *series2 << QPointF(0, 0)<< QPointF(90, 0) << QPointF(180, 0) << QPointF(270, 0) << QPointF(360, 0);
    
        chart->addSeries(series1);
        chart->addSeries(series2);
        chart->addAxis(angularAxis, QPolarChart::PolarOrientationAngular);
    
        QValueAxis *radialAxis = new QValueAxis();
        radialAxis->setTickCount(9);
        radialAxis->setLabelFormat("%d");
        chart->addAxis(radialAxis, QPolarChart::PolarOrientationRadial);
    
        series1->attachAxis(radialAxis);
        series1->attachAxis(angularAxis);
        series2->attachAxis(radialAxis);
        series2->attachAxis(angularAxis);
    
        radialAxis->setRange(-100, 100);
    
        QChartView *chartView = new QChartView();
        chartView->setChart(chart);
        chartView->setRenderHint(QPainter::Antialiasing);
    
        chartView->show();
    
        return a.exec();
    }
    

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