python - 如何计算 QPolygon 面积
问题描述
我正在尝试获得蓝色和绿色 QPolygon 的交集,以及由蓝色 QPolygon 组成的百分比(见下图)。
我创建的多边形如下:
import PyQt5
from PyQt5 import QtWidgets,QtGui,QtCore
from PyQt5.QtWidgets import *
from PyQt5.QtGui import *
from PyQt5.QtCore import *
import sys, math
class MyWidget(QtWidgets.QWidget):
def __init__(self, parent=None):
QtWidgets.QWidget.__init__(self, parent)
self.pen1 = QtGui.QPen(QtGui.QColor(20,0,250)) # set lineColor
self.pen = QtGui.QPen(QtGui.QColor(0,0,0)) # set lineColor
self.pen2 = QtGui.QPen(QtGui.QColor(0,250,0)) # set lineColor
self.pen.setWidth(3) # set lineWidth
self.brush = QtGui.QBrush(QtGui.QColor(255,255,255,10)) # set fillColor
coords = [PyQt5.QtCore.QPointF(640.0, 334.0), PyQt5.QtCore.QPointF(626.0, 462.0), PyQt5.QtCore.QPointF(782.0, 509.0), PyQt5.QtCore.QPointF(807.0, 373.0), PyQt5.QtCore.QPointF(807.0, 333.0)]
greenpolygoncoords = [PyQt5.QtCore.QPointF(698.0, 373.0), PyQt5.QtCore.QPointF(690.0, 433.0), PyQt5.QtCore.QPointF(757.0, 376.0), PyQt5.QtCore.QPointF(713.0, 351.0), PyQt5.QtCore.QPointF(713.0, 351.0), PyQt5.QtCore.QPointF(698.0, 373.0)]
self.bluepolygon = QPolygonF(coords)
self.greenpolygon =QPolygonF(greenpolygoncoords)
self.intersection = self.bluepolygon.intersected(self.greenpolygon)
print("overlap = "+str(self.intersection.size()/self.bluepolygon.size()))
def paintEvent(self, event):
painter = QtGui.QPainter(self)
painter.setPen(self.pen1)
painter.setBrush(self.brush)
painter.drawPolygon(self.bluepolygon) #bluepolygon = Blue
painter.setPen(self.pen)
painter.drawPolygon(self.intersection) #Intersection = black
painter.setPen(self.pen2)
painter.drawPolygon(self.greenpolygon) # greenpolygon = Green
app = QtWidgets.QApplication(sys.argv)
widget = MyWidget()
widget.show()
sys.exit(app.exec_())
但是,当我尝试计算两个多边形之间的重叠时,作为蓝色多边形的百分比,我得到了一个错误的答案(它说重叠等于 1,但是,绿色多边形肯定不构成 100%蓝色多边形)。
overlap = self.intersection.size()/self.bluepolygon.size()
查看由 QPolygon.size() 计算的大小时,很明显 QPolygon.size() 返回的多边形大小不正确。
print("size of blue polygon = "+str(self.bluepolygon.size()))
print("size of greenpolygon = "+str(self.greenpolygon.size()))
print("size of intersection = "+str(self.intersection.size()))
返回:
size of blue polygon = 5
size of greenpolygon = 6
size of intersection = 5
显然出于 PyQt5 的某些原因,蓝色多边形小于绿色多边形。怎么来的?
我究竟做错了什么?
解决方案
size() 方法不返回多边形的面积,而是返回边数或顶点数。如果要计算面积,则必须使用标准方法实现它:
def calculate_area(qpolygon):
area = 0
for i in range(qpolygon.size()):
p1 = qpolygon[i]
p2 = qpolygon[(i + 1) % qpolygon.size()]
d = p1.x() * p2.y() - p2.x() * p1.y()
area += d
return abs(area) / 2
然后你评估你想要什么:
print(
"overlap = "
+ str(calculate_area(self.intersection) / calculate_area(self.bluepolygon))
)
输出:
overlap = 0.0962288941619438
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