例程讲解18-MAVLink->mavlink_opticalflow 通过mavlink实现光流

# 通过mavlink实现光流
#
# 该脚本使用MAVLink协议向ArduPilot / PixHawk控制器发送光流检测，以使用您的OpenMV Cam进行位置控制。
#
# P4 = TXD

import image, math, pyb, sensor, struct, time

# 参数#################################################################

uart_baudrate = 115200

MAV_system_id = 1
MAV_component_id = 0x54
MAV_OPTICAL_FLOW_confidence_threshold = 0.1  
# 低于0.1左右（YMMV），结果只是噪音。

##############################################################################

# Link Setup

uart = pyb.UART(3, uart_baudrate, timeout_char = 1000)

# Helper Stuff

packet_sequence = 0

def checksum(data, extra): # https://github.com/mavlink/c_library_v1/blob/master/checksum.h
    output = 0xFFFF
    for i in range(len(data)):
        tmp = data[i] ^ (output & 0xFF)
        tmp = (tmp ^ (tmp << 4)) & 0xFF
        output = ((output >> 8) ^ (tmp << 8) ^ (tmp << 3) ^ (tmp >> 4)) & 0xFFFF
    tmp = extra ^ (output & 0xFF)
    tmp = (tmp ^ (tmp << 4)) & 0xFF
    output = ((output >> 8) ^ (tmp << 8) ^ (tmp << 3) ^ (tmp >> 4)) & 0xFFFF
    return output

MAV_OPTICAL_FLOW_message_id = 100
MAV_OPTICAL_FLOW_id = 0 # unused
MAV_OPTICAL_FLOW_extra_crc = 175

# http://mavlink.org/messages/common#OPTICAL_FLOW
# https://github.com/mavlink/c_library_v1/blob/master/common/mavlink_msg_optical_flow.h
def send_optical_flow_packet(x, y, c):
    global packet_sequence
    temp = struct.pack("<qfffhhbb",
                       0,
                       0,
                       0,
                       0,
                       int(x * 10),
                       int(y * 10),
                       MAV_OPTICAL_FLOW_id,
                       int(c * 255))
    temp = struct.pack("<bbbbb26s",
                       26,
                       packet_sequence & 0xFF,
                       MAV_system_id,
                       MAV_component_id,
                       MAV_OPTICAL_FLOW_message_id,
                       temp)
    temp = struct.pack("<b31sh",
                       0xFE,
                       temp,
                       checksum(temp, MAV_OPTICAL_FLOW_extra_crc))
    packet_sequence += 1
    uart.write(temp)

sensor.reset()                      # Reset and initialize the sensor.
sensor.set_pixformat(sensor.RGB565) # Set pixel format to RGB565 (or GRAYSCALE)
sensor.set_framesize(sensor.B64X32) # Set frame size to 64x32... (or 64x64)...
sensor.skip_frames(time = 2000)     # Wait for settings take effect.
clock = time.clock()                # Create a clock object to track the FPS.

# 从主帧缓冲区的RAM中取出以分配第二帧缓冲区。
# 帧缓冲区中的RAM比MicroPython堆中的RAM多得多。
# 但是，在执行此操作后，您的某些算法的RAM会少得多......
# 所以，请注意现在摆脱RAM问题要容易得多。
extra_fb = sensor.alloc_extra_fb(sensor.width(), sensor.height(), sensor.RGB565)
extra_fb.replace(sensor.snapshot())

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

    displacement = extra_fb.find_displacement(img)
    extra_fb.replace(img)

    # 没有滤波，偏移结果是嘈杂的，所以我们降低了一些精度。
    sub_pixel_x = int(displacement.x_translation() * 5) / 5.0
    sub_pixel_y = int(displacement.y_translation() * 5) / 5.0

    if(displacement.response() > MAV_OPTICAL_FLOW_confidence_threshold):
        send_optical_flow_packet(sub_pixel_x, sub_pixel_y, displacement.response())

        print("{0:+f}x {1:+f}y {2} {3} FPS".format(sub_pixel_x, sub_pixel_y,
              displacement.response(),
              clock.fps()))
    else:
        print(clock.fps())

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