使用DroneKit与PX4通讯

官网英文原文地址：http://dev.px4.io/dronekit-example.html

DroneKit可以帮助创建强大的无人机应用。这些应用运行在无人机的协同计算机上，通过执行计算密集但又需要低延迟的任务（计算机视觉）来增强飞控计算机。

DroneKit和PX4目前致力于获得完全兼容。截止DroneKit-python 2.2.0，仅提供任务处理和状态监控这样的基本支持。

配置DroneKit

首先，从当前主分支安装DroneKit-python

  1. git clone https://github.com/dronekit/dronekit-python.git
  2. cd ./dronekit-python
  3. sudo python setup.py build
  4. sudo python setup.py install

创建一个新的python文件并导入DroneKit, pymavlink和基本模块

  1. # Import DroneKit-Python
  2. from dronekit import connect, Command, LocationGlobal
  3. from pymavlink import mavutil
  4. import time, sys, argparse, math

连接到无人机或模拟器的MAVLink端口

  1. # Connect to the Vehicle
  2. print "Connecting"
  3. connection_string = '127.0.0.1:14540'
  4. vehicle = connect(connection_string, wait_ready=True)

显示一些基本的状态信息

  1. # Display basic vehicle state
  2. print " Type: %s" % vehicle._vehicle_type
  3. print " Armed: %s" % vehicle.armed
  4. print " System status: %s" % vehicle.system_status.state
  5. print " GPS: %s" % vehicle.gps_0
  6. print " Alt: %s" % vehicle.location.global_relative_frame.alt

完整的任务示例

下面的python脚本文件给出了使用DroneKit和PX4的完整任务范例。目前还不完全支持模式切换，因此我们发送自定义的模式切换指令。

  1. ################################################################################################
  2. # @File DroneKitPX4.py
  3. # Example usage of DroneKit with PX4
  4. #
  5. # @author Sander Smeets <sander@droneslab.com>
  6. #
  7. # Code partly based on DroneKit (c) Copyright 2015-2016, 3D Robotics.
  8. ################################################################################################
  10. # Import DroneKit-Python
  11. from dronekit import connect, Command, LocationGlobal
  12. from pymavlink import mavutil
  13. import time, sys, argparse, math
  16. ################################################################################################
  17. # Settings
  18. ################################################################################################
  20. connection_string       = '127.0.0.1:14540'
  21. MAV_MODE_AUTO   = 4
  22. # https://github.com/PX4/Firmware/blob/master/Tools/mavlink_px4.py
  25. # Parse connection argument
  26. parser = argparse.ArgumentParser()
  27. parser.add_argument("-c", "--connect", help="connection string")
  28. args = parser.parse_args()
  30. if args.connect:
  31.     connection_string = args.connect
  34. ################################################################################################
  35. # Init
  36. ################################################################################################
  38. # Connect to the Vehicle
  39. print "Connecting"
  40. vehicle = connect(connection_string, wait_ready=True)
  42. def PX4setMode(mavMode):
  43.     vehicle._master.mav.command_long_send(vehicle._master.target_system, vehicle._master.target_component,
  44.                                                mavutil.mavlink.MAV_CMD_DO_SET_MODE, 0,
  45.                                                mavMode,
  46.                                                0, 0, 0, 0, 0, 0)
  50. def get_location_offset_meters(original_location, dNorth, dEast, alt):
  51.     """
  52.     Returns a LocationGlobal object containing the latitude/longitude `dNorth` and `dEast` metres from the
  53.     specified `original_location`. The returned Location has the same `alt` value
  54.     as `original_location`.
  55.     The function is useful when you want to move the vehicle around specifying locations relative to
  56.     the current vehicle position.
  57.     The algorithm is relatively accurate over small distances (10m within 1km) except close to the poles.
  58.     For more information see:
  59.     http://gis.stackexchange.com/questions/2951/algorithm-for-offsetting-a-latitude-longitude-by-some-amount-of-meters
  60.     """
  61.     earth_radius=6378137.0 #Radius of "spherical" earth
  62.     #Coordinate offsets in radians
  63.     dLat = dNorth/earth_radius
  64.     dLon = dEast/(earth_radius*math.cos(math.pi*original_location.lat/180))
  66.     #New position in decimal degrees
  67.     newlat = original_location.lat + (dLat * 180/math.pi)
  68.     newlon = original_location.lon + (dLon * 180/math.pi)
  69.     return LocationGlobal(newlat, newlon,original_location.alt+alt)
  75. ################################################################################################
  76. # Listeners
  77. ################################################################################################
  79. home_position_set = False
  81. #Create a message listener for home position fix
  82. @vehicle.on_message('HOME_POSITION')
  83. def listener(self, name, home_position):
  84.     global home_position_set
  85.     home_position_set = True
  89. ################################################################################################
  90. # Start mission example
  91. ################################################################################################
  93. # wait for a home position lock
  94. while not home_position_set:
  95.     print "Waiting for home position..."
  96.     time.sleep(1)
  98. # Display basic vehicle state
  99. print " Type: %s" % vehicle._vehicle_type
  100. print " Armed: %s" % vehicle.armed
  101. print " System status: %s" % vehicle.system_status.state
  102. print " GPS: %s" % vehicle.gps_0
  103. print " Alt: %s" % vehicle.location.global_relative_frame.alt
  105. # Change to AUTO mode
  106. PX4setMode(MAV_MODE_AUTO)
  107. time.sleep(1)
  109. # Load commands
  110. cmds = vehicle.commands
  111. cmds.clear()
  113. home = vehicle.location.global_frame
  115. # takeoff to 10 meters
  116. wp = get_location_offset_meters(home, 0, 0, 10);
  117. cmd = Command(0,0,0, mavutil.mavlink.MAV_FRAME_GLOBAL_RELATIVE_ALT, mavutil.mavlink.MAV_CMD_NAV_TAKEOFF, 0, 1, 0, 0, 0, 0, wp.lat, wp.lon, wp.alt)
  118. cmds.add(cmd)
  120. # move 10 meters north
  121. wp = get_location_offset_meters(wp, 10, 0, 0);
  122. cmd = Command(0,0,0, mavutil.mavlink.MAV_FRAME_GLOBAL_RELATIVE_ALT, mavutil.mavlink.MAV_CMD_NAV_WAYPOINT, 0, 1, 0, 0, 0, 0, wp.lat, wp.lon, wp.alt)
  123. cmds.add(cmd)
  125. # move 10 meters east
  126. wp = get_location_offset_meters(wp, 0, 10, 0);
  127. cmd = Command(0,0,0, mavutil.mavlink.MAV_FRAME_GLOBAL_RELATIVE_ALT, mavutil.mavlink.MAV_CMD_NAV_WAYPOINT, 0, 1, 0, 0, 0, 0, wp.lat, wp.lon, wp.alt)
  128. cmds.add(cmd)
  130. # move 10 meters south
  131. wp = get_location_offset_meters(wp, -10, 0, 0);
  132. cmd = Command(0,0,0, mavutil.mavlink.MAV_FRAME_GLOBAL_RELATIVE_ALT, mavutil.mavlink.MAV_CMD_NAV_WAYPOINT, 0, 1, 0, 0, 0, 0, wp.lat, wp.lon, wp.alt)
  133. cmds.add(cmd)
  135. # move 10 meters west
  136. wp = get_location_offset_meters(wp, 0, -10, 0);
  137. cmd = Command(0,0,0, mavutil.mavlink.MAV_FRAME_GLOBAL_RELATIVE_ALT, mavutil.mavlink.MAV_CMD_NAV_WAYPOINT, 0, 1, 0, 0, 0, 0, wp.lat, wp.lon, wp.alt)
  138. cmds.add(cmd)
  140. # land
  141. wp = get_location_offset_meters(home, 0, 0, 10);
  142. cmd = Command(0,0,0, mavutil.mavlink.MAV_FRAME_GLOBAL_RELATIVE_ALT, mavutil.mavlink.MAV_CMD_NAV_LAND, 0, 1, 0, 0, 0, 0, wp.lat, wp.lon, wp.alt)
  143. cmds.add(cmd)
  145. # Upload mission
  146. cmds.upload()
  147. time.sleep(2)
  149. # Arm vehicle
  150. vehicle.armed = True
  152. # monitor mission execution
  153. nextwaypoint = vehicle.commands.next
  154. while nextwaypoint < len(vehicle.commands):
  155.     if vehicle.commands.next > nextwaypoint:
  156.         display_seq = vehicle.commands.next+1
  157.         print "Moving to waypoint %s" % display_seq
  158.         nextwaypoint = vehicle.commands.next
  159.     time.sleep(1)
  161. # wait for the vehicle to land
  162. while vehicle.commands.next > 0:
  163.     time.sleep(1)
  166. # Disarm vehicle
  167. vehicle.armed = False
  168. time.sleep(1)
  170. # Close vehicle object before exiting script
  171. vehicle.close()
  172. time.sleep(1)