# 线段检测

## code


# Find Line Segments Example
#
# This example shows off how to find line segments in the image. For each line object
# found in the image a line object is returned which includes the line's rotation.

# Note: Line detection is done by using the Hough Transform:
# http://en.wikipedia.org/wiki/Hough_transform
# Please read about it above for more information on what theta and rho are.

enable_lens_corr = True # turn on for straighter lines...

import sensor, image, time

sensor.reset()
sensor.set_pixformat(sensor.RGB565) # grayscale is faster
sensor.set_framesize(sensor.QQVGA)
sensor.skip_frames(time = 2000)
clock = time.clock()

# All lines also have x1(), y1(), x2(), and y2() methods to get their end-points
# and a line() method to get all the above as one 4 value tuple for 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...

# More about threshold - each pixel in the image contributes a magnitude value
# to a line. The sum of all contributions is the magintude for that line. Then
# when lines are merged their magnitudes are added togheter. Note that threshold
# filters out lines with low magnitudes before merging. To see the magnitude of
# un-merged lines set theta_margin and rho_margin to 0...

# theta_margin and rho_margin control merging similar lines. If two lines
# theta and rho value differences are less than the margins then they are merged.

# Setting both the above to zero will greatly increase segment detection at the
# cost of a lot of FPS. This is because when less lines are merged more pixels
# are tested... which takes longer but covers more possibilities...

# segment_threshold controls line segment extraction. It's a threshold on the
# magnitude response per pixel under an infinite line. Pixels with a magnitude
# above threshold are added to the line segment.

# find_line_segments merges detected lines that are no more than 5 pixels apart
# and no more than 15 degrees different to create nice continous line segments.

for l in img.find_line_segments(threshold = 1000, theta_margin = 15, rho_margin = 15, segment_threshold = 100):
img.draw_line(l.line(), color = (255, 0, 0))
# print(l)

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