joyplot.py

from qgis.core import Qgis, QgsMapLayer, QgsPointXY, QgsProject

from qgis.utils import iface


def create_joyplot():

    rlayer = iface.activeLayer()
    if rlayer.type() != QgsMapLayer.RasterLayer:
        iface.messageBar().pushMessage("Error", "Please select a DEM layer", level=Qgis.Critical)
        return

    crs = rlayer.crs()

    # create layer
    layer = QgsVectorLayer("Polygon?field=latitude:integer", "joy_plot", "memory")
    pr = layer.dataProvider()
    layer.setCrs(crs)

    y_steps = 60
    x_steps = 300
    vert_exag = 7

    extent = iface.mapCanvas().extent()
    height = extent.height()
    width = extent.width()
    x_min = extent.xMinimum()
    y_max = extent.yMaximum()
    y_step_size = height / y_steps
    x_step_size = width / x_steps

    for y_step in range(y_steps):
        poly = []
        y = y_max - (y_step * y_step_size)
        # create point lower so the line becomes a polygon with some depth
        first_point = QgsPointXY(x_min, y - y_step_size)
        poly.append(first_point)

        # add joyplot line for each step in y_steps
        for x_step in range(x_steps):
            x = x_min + (x_step * x_step_size)
            point = QgsPointXY(x, y)
            val, res = rlayer.dataProvider().sample(point, 1)
            if not res:
                val = 0
            if val < 0:
                val = 0
            poly.append(QgsPointXY(x, y + (val * vert_exag)))

        # add final point below to close the polygon
        last_point = poly[-1]
        last_pointx = last_point.x()
        last_pointy = y - y_step_size
        poly.append(QgsPointXY(last_pointx, last_pointy))

        out_feat = QgsFeature()
        out_feat.setGeometry(QgsGeometry.fromPolygonXY([poly]))
        out_feat.setAttributes([y_step])
        pr.addFeatures([out_feat])

    QgsProject.instance().addMapLayer(layer)

    layer.updateExtents()


create_joyplot()