Here is a Python node I wrote that subscribes to quaternions, converts quaternions to Euler angles, and then publish the Euler angles. The Euler angles are in a custom message, `my_pkg/msg/Eulers.msg`

:

```
Header header
float64 roll
float64 pitch
float64 yaw
```

Then create the file `my_pkg/quat_to_euler.py`

:

```
#!/usr/bin/python
# -*- coding: utf-8 -*-
# Start up ROS pieces.
PKG = 'my_pkg'
import roslib; roslib.load_manifest(PKG)
import rospy
import tf
# ROS messages.
from nav_msgs.msg import Odometry
from sensor_msgs.msg import Imu
from my_pkg.msg import Eulers
class QuatToEuler():
def __init__(self):
self.got_new_msg = False
self.euler_msg = Eulers()
# Create subscribers and publishers.
sub_imu = rospy.Subscriber("imu", Imu, self.imu_callback)
sub_odom = rospy.Subscriber("odom", Odometry, self.odom_callback)
pub_euler = rospy.Publisher("euler", Eulers)
# Main while loop.
while not rospy.is_shutdown():
# Publish new data if we got a new message.
if self.got_new_msg:
pub_euler.publish(self.euler_msg)
self.got_new_msg = False
# Odometry callback function.
def odom_callback(self, msg):
# Convert quaternions to Euler angles.
(r, p, y) = tf.transformations.euler_from_quaternion([msg.pose.pose.orientation.x, msg.pose.pose.orientation.y, msg.pose.pose.orientation.z, msg.pose.pose.orientation.w])
self.fill_euler_msg(msg, r, p, y)
# IMU callback function.
def imu_callback(self, msg):
# Convert quaternions to Euler angles.
(r, p, y) = tf.transformations.euler_from_quaternion([msg.orientation.x, msg.orientation.y, msg.orientation.z, msg.orientation.w])
self.fill_euler_msg(msg, r, p, y)
# Fill in Euler angle message.
def fill_euler_msg(self, msg, r, p, y):
self.got_new_msg = True
self.euler_msg.header.stamp = msg.header.stamp
self.euler_msg.roll = r
self.euler_msg.pitch = p
self.euler_msg.yaw = y
# Main function.
if __name__ == '__main__':
# Initialize the node and name it.
rospy.init_node('quat_to_euler')
# Go to class functions that do all the heavy lifting. Do error checking.
try:
quat_to_euler = QuatToEuler()
except rospy.ROSInterruptException: pass
```

In my launch file I start it with:

```
<node pkg="my_pkg" type="quat_to_euler.py" name="imu_euler_angles">
<remap from="imu" to="microstrain/data"/>
<remap from="euler" to="microstrain/euler"/>
</node>
<node pkg="my_pkg" type="quat_to_euler.py" name="kf_euler_angles">
<remap from="odom" to="kf/odom"/>
<remap from="euler" to="kf/euler"/>
</node>
```

Then you can plot your IMU roll vs. your KF roll (for example):

```
rxplot /microstrain/euler/roll:/kf/euler/roll
```