QtCharts test

test_qtcharts.py

from qgis.core import QgsVectorLayer, QgsFeatureRequest, QgsExpression

from PyQt5.QtCore import QPointF, QVariant, Qt
from PyQt5.QtWidgets import QWidget, QVBoxLayout, QHBoxLayout, QPushButton

from PyQt5.QtChart import QLineSeries, QChart, QChartView, QDateTimeAxis, QValueAxis

import numpy as np

def series_to_polyline(xdata, ydata):
    """Convert series data to QPolygon(F) polyline
    
    This code is derived from PythonQwt's function named 
    `qwt.plot_curve.series_to_polyline`"""
    size = len(xdata)
    polyline = QPolygonF(size)
    pointer = polyline.data()
    dtype, tinfo = np.float, np.finfo  # integers: = np.int, np.iinfo
    pointer.setsize(2*polyline.size()*tinfo(dtype).dtype.itemsize)
    memory = np.frombuffer(pointer, dtype)
    memory[:(size-1)*2+1:2] = xdata
    memory[1:(size-1)*2+2:2] = ydata
    return polyline

class MyPlot(QWidget):
    def __init__(self, parent=None):
        QWidget.__init__(self, parent)
        vbox = QVBoxLayout()
        hbox = QHBoxLayout()
        self.__zoom_in_btn = QPushButton("Zoom In")
        self.__zoom_out_btn = QPushButton("Zoom Out")

        self.__zoom_in_btn.clicked.connect(self.on_zoom_in)
        self.__zoom_out_btn.clicked.connect(self.on_zoom_out)

        self.__chart = QChart()
        self.__chart.legend().hide()
        chart_view = QChartView(self.__chart, self)

        hbox.addWidget(self.__zoom_in_btn)
        hbox.addWidget(self.__zoom_out_btn)
        vbox.addLayout(hbox)
        vbox.addWidget(chart_view)

        self.setLayout(vbox)
        self.resize(800,400)

    def add_data(self, data):
        series = QLineSeries(self)
        print("append data")
        for dt, val in data:
            if isinstance(dt, QVariant) and dt.isNull():
                continue
            series.append(QPointF(dt.toMSecsSinceEpoch(), val))

        self.__chart.addSeries(series)
        self.__chart.setTitle("Water conductivity over time")

        date_axis = QDateTimeAxis()
        date_axis.setFormat("dd/MM/yyyy HH:mm")
        self.__chart.addAxis(date_axis, Qt.AlignBottom)
        series.attachAxis(date_axis)

        value_axis = QValueAxis()
        value_axis.setMin(0.0)
        value_axis.setMax(1.0)
        self.__chart.addAxis(value_axis, Qt.AlignLeft)
        series.attachAxis(value_axis)

        #series.setPointLabelsFormat("@yPoint")
        #series.setPointLabelsVisible(True)
        series.setUseOpenGL(True)        

    def on_zoom_in(self):
        self.__chart.zoomIn()
    def on_zoom_out(self):
        self.__chart.zoomOut()
        

if __name__=='__main__':
    import sys

    from qgis.core import QgsApplication
    from PyQt5.QtWidgets import QApplication

    app = QgsApplication([s.encode('utf8') for s in sys.argv], True)
    #app = QApplication(sys.argv)
    QgsApplication.initQgis()

    measure_layer = QgsVectorLayer('service=bdlhes key="station_id,measure_time" table="measure"."water_conductivity"', "measure_layer", "postgres")
    req = QgsFeatureRequest(QgsExpression("station_id={}".format(2)))
    print("data from db")
    data = [(f["measure_time"], f["measure"]) for f in measure_layer.getFeatures(req)]

    p = MyPlot()
    p.add_data(data)

    print("render")
    p.show()
        
    app.exec_()

    QgsApplication.exitQgis()