PyQt5：QPolygonF 的中心线

Question

我正在尝试获取 QPolygonF 对象的中心线，这意味着对于从最小到最大的每个 y 坐标，位于最小和最大 X 坐标中间的线。

所需的输出将是一条中心线，但由于某种原因，绘制的对象/中心线有面积。为什么会这样？我应该怎么做才能获得中心线？如下图黑线粗略估计

代码如下：

import PyQt5
from PyQt5 import QtGui
from PyQt5.QtWidgets import QApplication,QWidget, QMainWindow,QVBoxLayout, QGraphicsScene, QGraphicsPixmapItem,QGraphicsView
from PyQt5.QtGui import QPixmap,QPolygonF
from PyQt5.QtCore import Qt,QPointF
import sys
import time
class MainWindow(QMainWindow):

    def __init__(self, *args, **kwargs):
        super(MainWindow, self).__init__(*args, **kwargs)
        self.setFixedSize(1200, 800)

        self.ImageDisplay = QGraphicsView()

        self.qwidget = QWidget()

        qpixmap = QPixmap()
        qpixmap2 = qpixmap.scaledToWidth(self.ImageDisplay.width())
        qgraphicsitem = QGraphicsPixmapItem(qpixmap2)
        qscene = QGraphicsScene(self.ImageDisplay)
        qscene.addItem(qgraphicsitem)
        self.ImageDisplay.setScene(qscene)
        self.ImageDisplay.setMouseTracking(True)
        self.ImageDisplay.setTransformationAnchor(QGraphicsView.AnchorUnderMouse)
        self.ImageDisplay.setResizeAnchor(QGraphicsView.AnchorUnderMouse)
        self.ImageDisplay.setVerticalScrollBarPolicy(Qt.ScrollBarAlwaysOff)
        self.ImageDisplay.setHorizontalScrollBarPolicy(Qt.ScrollBarAlwaysOff)
        start = time.time()

        poly = QPolygonF([QPointF(400, 400), QPointF(100, 10), QPointF(20, 100), QPointF(0, 400)])#, QPointF(105, 5), QPointF(9, 300)])

        min_y, max_y = poly.boundingRect().y(), poly.boundingRect().y() + poly.boundingRect().height()
        min_x,max_x =  poly.boundingRect().x(), poly.boundingRect().x() + poly.boundingRect().width()
        print("min_y="+str(min_y)+", max_y="+str(max_y))
        print("min_x=" + str(min_x) + ", max_x=" + str(max_x))
        end = time.time()
        print(f"runtime: {end - start}")

        middle_points= []
        for y in range(int(min_y),int(max_y)):
           # for x in range(int(min_x),int(max_x)):
            polyline = QPolygonF([QPointF(min_x,y),QPointF(max_x,y),QPointF(min_x,y+0.1),QPointF(max_x,y+0.1)])

            intersection_points = poly.intersected(polyline)


            intersection_points = intersection_points.boundingRect()

            middle_point = QPointF(intersection_points.x()+intersection_points.width()/2,intersection_points.y()+intersection_points.height()/2)
            middle_points.append(middle_point)


        middle_poly = QPolygonF(middle_points)
        self.ImageDisplay.scene().addPolygon(middle_poly, QtGui.QColor(20, 0, 255, 28),
                                             QtGui.QColor(20, 0, 255, 28))

        end = time.time()
        print(f"runtime: {end - start}")






        self.vlayout = QVBoxLayout()
        self.vlayout.addWidget(self.ImageDisplay)

        self.qwidget.setLayout(self.vlayout)

        self.setCentralWidget(self.qwidget)


app = QApplication(sys.argv)
window = MainWindow()
window.show()
app.exec_()

Answer 1

你必须考虑到：

当添加 QPolygon 时，将绘制一个闭合图形。
不是一条中心线，而是一条由线段组成的中心曲线
代码 for y in range(int(min_y),int(max_y)): 适用于 (ymax-ymin) 大于 1 但在其他情况下失败。

要绘制中心曲线，除了使用np.arange().

外，还必须使用QPainterPath

import sys

from PyQt5.QtCore import QPointF, QRectF
from PyQt5.QtGui import QPainterPath, QPolygonF
from PyQt5.QtWidgets import QApplication, QGraphicsScene, QGraphicsView

import numpy as np


def build_center_line(polygon):
    points = []
    minx, miny, maxx, maxy = polygon.boundingRect().getCoords()
    dy = (maxy - miny) / 200
    for y in np.arange(miny, maxy, dy):
        polyline = QPolygonF(
            QRectF(QPointF(minx, y - dy / 2), QPointF(maxx, y + dy / 2))
        )
        p = polygon.intersected(polyline).boundingRect().center()
        points.append(p)
    return points


def main():
    app = QApplication(sys.argv)
    polygon = QPolygonF(
        [QPointF(400, 400), QPointF(100, 10), QPointF(20, 100), QPointF(0, 400)]
    )

    points = build_center_line(polygon)
    path = QPainterPath()
    if points:
        path.moveTo(points[0])
        for point in points[1:]:
            path.lineTo(point)

    scene = QGraphicsScene()
    view = QGraphicsView(scene)
    scene.addPolygon(polygon)
    scene.addPath(path)
    view.resize(640, 480)
    view.show()

    sys.exit(app.exec_())


if __name__ == "__main__":
    main()

PyQt5：QPolygonF 的中心线

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