需求描述

• 在一张CAD图上需要知道墙角，并且标注出来，设想先检测出两面墙壁，即两条直线，然后计算线的交点即可

解决过程

1. 首先要在python里面opencv库，之后读取图片，然后是直线检测前常规性的转灰度图、高斯模糊、边缘检测，再用获夫变换检测直线。

# -*- coding: UTF-8 -*-
import cv2
import numpy as np
#图片路径
imgPath="xxx.png"
img=cv2.imread(imgPath)
#转灰度图
gray=cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
#高斯模糊
gray=cv2.GaussianBlur(gray,(3,3),0)
#边缘检测
edges = cv2.Canny(gray, 400, 400)
#霍夫变换
lines = cv2.HoughLinesP(edges, 1, np.pi / 180, 25, minLineLength=650, maxLineGap=8)

2. 计算两条直线的交点函数

def cross_point(line1, line2):  # 计算交点函数
    #是否存在交点
    point_is_exist=False
    x=0
    y=0
    x1 = line1[0]  # 取四点坐标
    y1 = line1[1]
    x2 = line1[2]
    y2 = line1[3]

    x3 = line2[0]
    y3 = line2[1]
    x4 = line2[2]
    y4 = line2[3]

    if (x2 - x1) == 0:
        k1 = None
    else:
        k1 = (y2 - y1) * 1.0 / (x2 - x1)  # 计算k1,由于点均为整数，需要进行浮点数转化
        b1 = y1 * 1.0 - x1 * k1 * 1.0  # 整型转浮点型是关键

    if (x4 - x3) == 0:  # L2直线斜率不存在操作
        k2 = None
        b2 = 0
    else:
        k2 = (y4 - y3) * 1.0 / (x4 - x3)  # 斜率存在操作
        b2 = y3 * 1.0 - x3 * k2 * 1.0

    if k1 is None:
        if not k2 is None:
            x = x1
            y = k2 * x1 + b2
            point_is_exist=True
    elif k2 is None:
        x=x3
        y=k1*x3+b1
    elif not k2==k1:
        x = (b2 - b1) * 1.0 / (k1 - k2)
        y = k1 * x * 1.0 + b1 * 1.0
        point_is_exist=True
    return point_is_exist,[x, y]

3. 完整代码

# -*- coding: UTF-8 -*-
import cv2
import numpy as np
def cross_point(line1, line2):  # 计算交点函数
    #是否存在交点
    point_is_exist=False
    x=0
    y=0
    x1 = line1[0]  # 取四点坐标
    y1 = line1[1]
    x2 = line1[2]
    y2 = line1[3]

    x3 = line2[0]
    y3 = line2[1]
    x4 = line2[2]
    y4 = line2[3]

    if (x2 - x1) == 0:
        k1 = None
    else:
        k1 = (y2 - y1) * 1.0 / (x2 - x1)  # 计算k1,由于点均为整数，需要进行浮点数转化
        b1 = y1 * 1.0 - x1 * k1 * 1.0  # 整型转浮点型是关键

    if (x4 - x3) == 0:  # L2直线斜率不存在操作
        k2 = None
        b2 = 0
    else:
        k2 = (y4 - y3) * 1.0 / (x4 - x3)  # 斜率存在操作
        b2 = y3 * 1.0 - x3 * k2 * 1.0

    if k1 is None:
        if not k2 is None:
            x = x1
            y = k2 * x1 + b2
            point_is_exist=True
    elif k2 is None:
        x=x3
        y=k1*x3+b1
    elif not k2==k1:
        x = (b2 - b1) * 1.0 / (k1 - k2)
        y = k1 * x * 1.0 + b1 * 1.0
        point_is_exist=True
    return point_is_exist,[x, y]
#图片路径
imgPath="xxx.png"
img=cv2.imread(imgPath)
#转灰度图
gray=cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
#高斯模糊
gray=cv2.GaussianBlur(gray,(3,3),0)
#边缘检测
edges = cv2.Canny(gray, 400, 400)
#霍夫变换
lines = cv2.HoughLinesP(edges, 1, np.pi / 180, 25, minLineLength=650, maxLineGap=8)
lines1 =lines[:, 0, :]# 提取为二维
for x1, y1, x2, y2 in lines1[:]:
    cv2.line(img, (x1, y1), (x2, y2), (0, 0, 255), 2)

for x1, y1, x2, y2 in lines1[:]:
    for x3,y3,x4,y4 in lines1[:]:
        point_is_exist, [x, y]=cross_point([x1, y1, x2, y2],[x3,y3,x4,y4])
        if point_is_exist:
            cv2.circle(img,(int(x),int(y)),5,(0,0,255),3)
cv2.imshow('Result', img)
cv2.waitKey (0)

遗留问题

• 直线检测部分本来想尝试LSD直线检测算法，网上找到的代码如下

lsd=cv2.createLineSegmentDetector(0)
lines=lsd.detect(img)[0]
drawn_img=lsd.drawSegments(img,lines)
cv2.imshow("LSD",drawn_img )
cv2.waitKey(0)

但是运行的时候会遇到如下问题，以后有机会可以尝试去解决一下。

Traceback (most recent call last):
  File "LineDetect.py", line 61, in <module>
    lsd=cv2.createLineSegmentDetector(0)
cv2.error: OpenCV(4.1.0) /Users/travis/build/skvark/opencv-python/opencv/modules/imgproc/src/lsd.cpp:143: error: (-213:The function/feature is not implemented) Implementation has been removed due original code license issues in function 'LineSegmentDetectorImpl'