Routine explanation -09-lines Identify straight lines

Video tutorial 13 - Shape recognition: https://singtown.com/learn/50009/

This routine is 09-feature-Detection-lines.py\ The purpose of this routine is to use the canny operator and Hough transform for line recognition.\ In the future, the official should update the Hough transform to recognize the shape function.

# 识别直线例程
#
# 这个例子展示了如何在图像中查找线条。对于在图像中找到的每个线对象，
# 都会返回一个包含线条旋转的线对象。

# 注意：线条检测是通过使用霍夫变换完成的：
# http://en.wikipedia.org/wiki/Hough_transform
# 请阅读以上关于“theta”和“rho”的更多信息。

# find_lines（）找到无限长度的线。使用find_line_segments（）
# 来查找非无限线。

enable_lens_corr = False # turn on for straighter lines...打开以获得更直的线条…
import sensor, image, time

sensor.reset()
sensor.set_pixformat(sensor.RGB565) #灰度更快
sensor.set_framesize(sensor.QQVGA)
sensor.skip_frames(time = 2000)
clock = time.clock()

# 所有的线对象都有一个`theta（）`方法来获取它们的旋转角度。
# 您可以根据旋转角度来过滤线条。

min_degree = 0
max_degree = 179

# 所有线段都有 `x1()`, `y1()`, `x2()`, and `y2()` 方法来获得他们的终点
# 一个 `line()` 方法来获得所有上述的四个元组值，可用于 `draw_line()`.

while(True):
    clock.tick()
    img = sensor.snapshot()
    if enable_lens_corr: img.lens_corr(1.8) # for 2.8mm lens...

    # `threshold` controls how many lines in the image are found. Only lines with
    # edge difference magnitude sums greater than `threshold` are detected...

    # `threshold`控制从霍夫变换中监测到的直线。只返回大于或等于阈值的
    # 直线。应用程序的阈值正确值取决于图像。注意：一条直线的大小是组成
    # 直线所有索贝尔滤波像素大小的总和。

    # `theta_margin`和`rho_margin`控件合并相似的直线。如果两直线的
    # theta和ρ值差异小于边际，则它们合并。

    for l in img.find_lines(threshold = 1000, theta_margin = 25, rho_margin = 25):
        if (min_degree <= l.theta()) and (l.theta() <= max_degree):
            img.draw_line(l.line(), color = (255, 0, 0))
            # print(l)

    print("FPS %f" % clock.fps())

# About negative rho values:
# 关于负rho值:
#
# A [theta+0:-rho] tuple is the same as [theta+180:+rho].
# A [theta+0:-rho]元组与[theta+180:+rho]相同。

original image：\

The effect of running the program is as follows:

Singtown Technology OpenMV official Chinese document function explanation: