ROS中IMU消息的定义：
sensor_msgs/Imu.msg
# This is a message to hold data from an IMU (Inertial Measurement Unit)
#
# Accelerations should be in m/s^2 (not in g's), and rotational velocity should be in rad/sec
#
# If the covariance of the measurement is known, it should be filled in (if all you know is the
# variance of each measurement, e.g. from the datasheet, just put those along the diagonal)
# A covariance matrix of all zeros will be interpreted as "covariance unknown", and to use the
# data a covariance will have to be assumed or gotten from some other source
#
# If you have no estimate for one of the data elements (e.g. your IMU doesn't produce an orientation
# estimate), please set element 0 of the associated covariance matrix to -1
# If you are interpreting this message, please check for a value of -1 in the first element of each
# covariance matrix, and disregard the associated estimate.
Header header
geometry_msgs/Quaternion orientation
float64[9] orientation_covariance # Row major about x, y, z axes
geometry_msgs/Vector3 angular_velocity
float64[9] angular_velocity_covariance # Row major about x, y, z axes
geometry_msgs/Vector3 linear_acceleration
float64[9] linear_acceleration_covariance # Row major x, y z
有点不明白的是这里明明写着Quaternion，但是有人却直接给orientation赋值欧拉角，找了一些资料，发现好像都可以，也就是说ROS内部会自行转换。
我们是在2D进行导航，那么：quaternion中（x,y,z,w），x，y可以直接赋0，z和w赋相应的值。
2
获取到imu数据之后，发布Imu消息
robot_pose_ekf接收imu消息和odometry消息，进行融合后发布
