我想要识别矩形，并测出旋转角度，如何实现

# Find Rects Example
#
# 这个例子展示了如何使用april标签代码中的四元检测代码在图像中找到矩形。 四元检测算法以非常稳健的方式检测矩形，并且比基于Hough变换的方法好得多。 例如，即使镜头失真导致这些矩形看起来弯曲，它仍然可以检测到矩形。 圆角矩形是没有问题的！
# (但是，这个代码也会检测小半径的圆)...

import sensor, image, time
from pyb import UART
import json

sensor.reset()
sensor.set_pixformat(sensor.RGB565) # 灰度更快(160x120 max on OpenMV-M7)
sensor.set_framesize(sensor.QQVGA)
sensor.skip_frames(time = 2000)
clock = time.clock()
uart = UART(3, 115200)
uart.init(115200,bits=8,parity=None,stop=1,timeout_char=1000)

while(True):
    clock.tick()
    img = sensor.snapshot()

    # 下面的`threshold`应设置为足够高的值，以滤除在图像中检测到的具有
    # 低边缘幅度的噪声矩形。最适用与背景形成鲜明对比的矩形。

    for r in img.find_rects(threshold = 10000):
        img.draw_rectangle(r.rect(), color = (255, 0, 0))
        for p in r.corners(): img.draw_circle(p[0], p[1], 5, color = (0, 255, 0))
        #print(r)
        data = r.corners()
        print(data)
        uart.write(data)
    
    #print("FPS %f" % clock.fps())

import sensor, image, time, math

threshold=(60, 255, -20, 20, -20, 20) # 激光灯在纸上颜色的阈值，可以执行调节
from pyb import Pin
sensor.reset()
sensor.set_auto_gain(False)
sensor.set_pixformat(sensor.GRAYSCALE) # or sensor.RGB565
sensor.set_framesize(sensor. QVGA) # or sensor.QVGA (or others)
sensor.skip_frames(time=900) # Let new settings take affect.
sensor.set_auto_exposure(False, 1000)#在这里调节曝光度，调节完可以比较清晰地看清激光点
sensor.set_auto_whitebal(False) # turn this off.
sensor.set_auto_gain(False) # 关闭增益（色块识别时必须要关）
clock = time.clock() # Tracks FPS.

def color_blob(threshold):

blobs = img.find_blobs([threshold,x_stride=1, y_stride=1, area_threshold=0, pixels_threshold=0,merge=False,margin=1])

if len(blobs)>=1 :#有色块
    # Draw a rect around the blob.
    b = blobs[0]
    img.draw_rectangle(b[0:4]) # rect
    cx = b[5]
    cy = b[6]
    for i in range(len(blobs)-1):
        img.draw_rectangle(b[0:4]) # rect
        cx = blobs[i][5]+cx
        cy = blobs[i][6]+cy
    cx=int(cx/len(blobs))
    cy=int(cy/len(blobs))
    img.draw_cross(cx, cy) # cx, cy
    print(cx,cy)
    return int(cx), int(cy)
return -1, -1 #表示没有找到

while(True):
clock.tick() # Track elapsed milliseconds between snapshots().
img = sensor.snapshot() # Take a picture and return the image.

blobs = img.find_blobs([threshold])
if blobs:
    max_blob = color_blob(threshold)
    pan_error = max_blob.cx()-img.width()/2
    tilt_error = max_blob.cy()-img.height()/2

    print("pan_error: ", pan_error)

    img.draw_rectangle(max_blob.rect()) # rect
    img.draw_cross(max_blob.cx(), max_blob.cy()) # cx, cy

    pan_output=pan_pid.get_pid(pan_error,1)/2
    tilt_output=tilt_pid.get_pid(tilt_error,1)
    print("pan_output",pan_output)
    pan_servo.angle(pan_servo.angle()+pan_output)
    tilt_servo.angle(tilt_servo.angle()-tilt_output)

blobs = img.find_blobs([threshold,x_stride=1, y_stride=1, area_threshold=0, pixels_threshold=0,merge=False,margin=1])