openmv/usr/examples/18-MAVLink/mavlink_opticalflow.py
Kwabena W. Agyeman a039b5d1c7 Change skip_frames() to use a 2 second timeout.
This was necessary due to the increase in the frame rate. The previous
method did not correlate to time.

All scripts updated.
2017-05-27 19:31:41 -04:00

92 lines
2.8 KiB
Python

# MAVLink OpticalFlow Script.
#
# This script sends out OpticalFlow detections using the MAVLink protocol to
# an ArduPilot/PixHawk controller for position control using your OpenMV Cam.
#
# P4 = TXD
import image, math, pyb, sensor, struct, time
# Parameters #################################################################
uart_baudrate = 115200
MAV_system_id = 1
MAV_component_id = 0x54
MAV_OPTICAL_FLOW_confidence_threshold = 0.2
##############################################################################
# Camera Setup
sensor.reset()
sensor.set_pixformat(sensor.GRAYSCALE)
sensor.set_framesize(sensor.QQVGA)
sensor.skip_frames(time = 2000)
# 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 * 4), # up sample by 4
int(y * 10 * 4), # up sample by 4
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)
# Main Loop
clock = time.clock()
old_img = sensor.snapshot().mean_pooled(4, 4) # 160x120 -> 40x30
while(True):
clock.tick()
new_img = sensor.snapshot().mean_pooled(4, 4) # 160x120 -> 40x30
x, y, c = new_img.find_displacement(old_img)
old_img = new_img
if (not (math.isnan(x) or math.isnan(y) or math.isnan(c))) and (c > MAV_OPTICAL_FLOW_confidence_threshold):
send_optical_flow_packet(-x, -y, c)
print("dx %10f, dy %10f, confidence %10f - FPS %f" % (-x, -y, c, clock.fps()))
else:
print("FPS %f" % (clock.fps()))