QT5 QML图表：如何仅标记特定点

Question

默认情况下，在QML Charts LineSeries中标记所有点。我只需要标明具体点，如何实现这一点？

这是我的qml文件（大项目的一部分）。 我已经为LineSeries设置了相应的属性来显示点标签，但我只需要显示几个标签而不是完整的点集。 Qml中有没有办法控制它？

import QtQuick 2.7
import QtCharts 2.2
import QtQuick.Layouts 1.3
import aa.ui.backend 1.0

Item {
property DSPBackend backend: analyzer.dsp

property alias titleV: chartV.title
property alias seriesV: lineSeriesV
property alias titleI: chartI.title
property alias seriesI: lineSeriesI

GridLayout {
    id: gridSpectrum
    anchors.fill: parent
    columns: 2
    rows: 1
    columnSpacing: 0
    flow: GridLayout.LeftToRight

    ChartView {
        id: chartV
        Layout.fillWidth: true
        Layout.fillHeight: true
        /*title: "Spectrum (V-channel)"
        titleFont.pixelSize: 10*/
        theme: ChartView.ChartThemeBlueCerulean
        antialiasing: false
        legend.visible: false
        legend.font.pointSize: 10
        margins.top: 2
        margins.left: 2
        margins.right: 2
        margins.bottom: 4

        ValueAxis {
            id: axisXV
            titleFont.pointSize: 7
            labelsFont.pointSize: 7
        }

        ValueAxis {
            id: axisYV
            titleFont.pointSize: 7
            labelsFont.pointSize: 7
        }

        LineSeries {
            id: lineSeriesV
            axisX: axisXV
            axisY: axisYV
            color: "#66cc00"
            name: "V-channel"
            pointLabelsFormat: "(@xPoint Hz, @yPoint dB)"
            pointLabelsVisible: true
            width: 3
            useOpenGL: false
        }
    }

    ChartView {
        id: chartI
        /*title: "Spectrum (I-channel)"
        titleFont.pixelSize: 10*/
        antialiasing: true
        theme: ChartView.ChartThemeBlueCerulean
        legend.visible: false
        legend.font.pointSize: 10
        margins.top: 2
        margins.left: 2
        margins.right: 2
        margins.bottom: 4
        Layout.fillWidth: true
        Layout.fillHeight: true

        ValueAxis {
            id: axisXI
            titleFont.pointSize: 7
            labelsFont.pointSize: 7
        }

        ValueAxis {
            id: axisYI
            titleFont.pointSize: 7
            labelsFont.pointSize: 7
        }

        LineSeries {
            id: lineSeriesI
            axisX: axisXI
            axisY: axisYI
            color: "#0099ff"
            name: "I-channel"
            pointLabelsFormat: "(@xPoint Hz, @yPoint dB)"
            pointLabelsVisible: true
            width: 3
            useOpenGL: false
        }

    }

}

Timer {
    id: timerSpectrum
    interval: 500
    running: true
    repeat: true
    onTriggered: {
        backend.update_spectrum(seriesV, seriesI);
    }
}

Component.onCompleted: {
    backend.setup_spectrum(axisXV, axisYV, axisXI, axisYI)
}
}