Example: Create Attribute in App¶

#!/usr/bin/env python
# -*- coding: utf-8 -*-

"""
© Copyright 2015-2016, 3D Robotics.

create_attribute.py:

Demonstrates how to create attributes from MAVLink messages within your DroneKit-Python script 
and use them in the same way as the built-in Vehicle attributes.

The code adds a new attribute to the Vehicle class, populating it with information from RAW_IMU messages 
intercepted using the message_listener decorator.

Full documentation is provided at http://python.dronekit.io/examples/create_attribute.html
"""
from __future__ import print_function

from dronekit import connect, Vehicle
from my_vehicle import MyVehicle #Our custom vehicle class
import time



#Set up option parsing to get connection string
import argparse  
parser = argparse.ArgumentParser(description='Demonstrates how to create attributes from MAVLink messages. ')
parser.add_argument('--connect', 
                   help="Vehicle connection target string. If not specified, SITL automatically started and used.")
args = parser.parse_args()

connection_string = args.connect
sitl = None


#Start SITL if no connection string specified
if not connection_string:
    import dronekit_sitl
    sitl = dronekit_sitl.start_default()
    connection_string = sitl.connection_string()


# Connect to the Vehicle
print('Connecting to vehicle on: %s' % connection_string)
vehicle = connect(connection_string, wait_ready=True, vehicle_class=MyVehicle)

# Add observer for the custom attribute

def raw_imu_callback(self, attr_name, value):
    # attr_name == 'raw_imu'
    # value == vehicle.raw_imu
    print(value)

vehicle.add_attribute_listener('raw_imu', raw_imu_callback)

print('Display RAW_IMU messages for 5 seconds and then exit.')
time.sleep(5)

#The message listener can be unset using ``vehicle.remove_message_listener``

#Close vehicle object before exiting script
print("Close vehicle object")
vehicle.close()

# Shut down simulator if it was started.
if sitl is not None:
    sitl.stop()

#!/usr/bin/env python
# -*- coding: utf-8 -*-

"""
© Copyright 2015-2016, 3D Robotics.

my_vehicle.py:

Custom Vehicle subclass to add IMU data.
"""

from dronekit import Vehicle


class RawIMU(object):
    """
    The RAW IMU readings for the usual 9DOF sensor setup. 
    This contains the true raw values without any scaling to allow data capture and system debugging.
    
    The message definition is here: https://mavlink.io/en/messages/common.html#RAW_IMU
    
    :param time_boot_us: Timestamp (microseconds since system boot). #Note, not milliseconds as per spec
    :param xacc: X acceleration (mg)
    :param yacc: Y acceleration (mg)
    :param zacc: Z acceleration (mg)
    :param xgyro: Angular speed around X axis (millirad /sec)
    :param ygyro: Angular speed around Y axis (millirad /sec)
    :param zgyro: Angular speed around Z axis (millirad /sec)
    :param xmag: X Magnetic field (milli tesla)
    :param ymag: Y Magnetic field (milli tesla)
    :param zmag: Z Magnetic field (milli tesla)    
    """
    def __init__(self, time_boot_us=None, xacc=None, yacc=None, zacc=None, xygro=None, ygyro=None, zgyro=None, xmag=None, ymag=None, zmag=None):
        """
        RawIMU object constructor.
        """
        self.time_boot_us = time_boot_us
        self.xacc = xacc
        self.yacc = yacc
        self.zacc = zacc
        self.xgyro = zgyro
        self.ygyro = ygyro
        self.zgyro = zgyro
        self.xmag = xmag        
        self.ymag = ymag
        self.zmag = zmag      
        
    def __str__(self):
        """
        String representation used to print the RawIMU object. 
        """
        return "RAW_IMU: time_boot_us={},xacc={},yacc={},zacc={},xgyro={},ygyro={},zgyro={},xmag={},ymag={},zmag={}".format(self.time_boot_us, self.xacc, self.yacc,self.zacc,self.xgyro,self.ygyro,self.zgyro,self.xmag,self.ymag,self.zmag)

   
class MyVehicle(Vehicle):
    def __init__(self, *args):
        super(MyVehicle, self).__init__(*args)

        # Create an Vehicle.raw_imu object with initial values set to None.
        self._raw_imu = RawIMU()

        # Create a message listener using the decorator.   
        @self.on_message('RAW_IMU')
        def listener(self, name, message):
            """
            The listener is called for messages that contain the string specified in the decorator,
            passing the vehicle, message name, and the message.
            
            The listener writes the message to the (newly attached) ``vehicle.raw_imu`` object 
            and notifies observers.
            """
            self._raw_imu.time_boot_us=message.time_usec
            self._raw_imu.xacc=message.xacc
            self._raw_imu.yacc=message.yacc
            self._raw_imu.zacc=message.zacc
            self._raw_imu.xgyro=message.xgyro
            self._raw_imu.ygyro=message.ygyro
            self._raw_imu.zgyro=message.zgyro
            self._raw_imu.xmag=message.xmag
            self._raw_imu.ymag=message.ymag
            self._raw_imu.zmag=message.zmag
            
            # Notify all observers of new message (with new value)
            #   Note that argument `cache=False` by default so listeners
            #   are updated with every new message
            self.notify_attribute_listeners('raw_imu', self._raw_imu) 

    @property
    def raw_imu(self):
        return self._raw_imu