例程讲解23-April-Tags->find_apriltags 寻找Apriltag

视频教程11 - AprilTag标记追踪：https://singtown.com/learn/49590/

视频教程21 - 追其他物体的小车：https://singtown.com/learn/50041/

# AprilTags 示例
#
# 此示例显示了OpenMV Cam在OpenMV Cam M7上检测April标签的强大功能。
# OpenMV2 M4版本无法检测April标签。

import sensor, image, time, math

sensor.reset()
sensor.set_pixformat(sensor.RGB565)
sensor.set_framesize(sensor.QQVGA) # we run out of memory if the resolution is much bigger...
sensor.skip_frames(time = 2000)
sensor.set_auto_gain(False)  # must turn this off to prevent image washout...
sensor.set_auto_whitebal(False)  # must turn this off to prevent image washout...
clock = time.clock()

# 注意！与find_qrcodes不同，find_apriltags方法不需要对图像进行镜头校正

# apriltag代码最多支持可以同时处理6种tag家族。
# 返回的tag标记对象，将有其tag标记家族及其在tag标记家族内的id。

tag_families = 0
tag_families |= image.TAG16H5 # comment out to disable this family
tag_families |= image.TAG25H7 # comment out to disable this family
tag_families |= image.TAG25H9 # comment out to disable this family
tag_families |= image.TAG36H10 # comment out to disable this family
tag_families |= image.TAG36H11 # comment out to disable this family (default family)
tag_families |= image.ARTOOLKIT # comment out to disable this family

#标签系列有什么区别？ 那么，例如，TAG16H5家族实际上是一个4x4的方形标签。 
#所以，这意味着可以看到比6x6的TAG36H11标签更长的距离。 
#然而，较低的H值（H5对H11），意味着4x4标签的假阳性率远高于6x6标签。 
#所以，除非你有理由使用其他标签系列，否则使用默认族TAG36H11。



def family_name(tag):
    if(tag.family() == image.TAG16H5):
        return "TAG16H5"
    if(tag.family() == image.TAG25H7):
        return "TAG25H7"
    if(tag.family() == image.TAG25H9):
        return "TAG25H9"
    if(tag.family() == image.TAG36H10):
        return "TAG36H10"
    if(tag.family() == image.TAG36H11):
        return "TAG36H11"
    if(tag.family() == image.ARTOOLKIT):
        return "ARTOOLKIT"

while(True):
    clock.tick()
    img = sensor.snapshot()
    for tag in img.find_apriltags(families=tag_families): # defaults to TAG36H11 without "families".
        img.draw_rectangle(tag.rect(), color = (255, 0, 0))
        img.draw_cross(tag.cx(), tag.cy(), color = (0, 255, 0))
        print_args = (family_name(tag), tag.id(), (180 * tag.rotation()) / math.pi)
        print("Tag Family %s, Tag ID %d, rotation %f (degrees)" % print_args)
    print(clock.fps())

星瞳科技OpenMV官方中文文档函数讲解：

扩展阅读：

• 来自星瞳实验室APP: Apriltag识别中，怎么定位/测距？输出的tx ty tz的单位是什么？怎么就得到实际的距离了？https://forum.singtown.com/topic/52