ROS Message Types Reference

This skill provides comprehensive information about ROS message types commonly used in robotics applications.

Quick Message Lookup

Use these commands to inspect any message type:

bash

# Show message structure
rosmsg show sensor_msgs/Imu

# List all messages in a package
rosmsg package sensor_msgs

# Find messages by name pattern
rosmsg list | grep -i imu

sensor_msgs - Sensor Data Messages

sensor_msgs/Imu

IMU (Inertial Measurement Unit) data.

code

std_msgs/Header header
  uint32 seq
  time stamp
  string frame_id
geometry_msgs/Quaternion orientation
  float64 x, y, z, w
float64[9] orientation_covariance
geometry_msgs/Vector3 angular_velocity
  float64 x, y, z
float64[9] angular_velocity_covariance
geometry_msgs/Vector3 linear_acceleration
  float64 x, y, z
float64[9] linear_acceleration_covariance

Units:

•angular_velocity: rad/s
•linear_acceleration: m/s^2
•orientation: quaternion (unitless)

Covariance: Row-major 3x3 matrix. Set first element to -1 if data not available.

Example - Publishing IMU:

python

from sensor_msgs.msg import Imu
msg = Imu()
msg.header.stamp = rospy.Time.now()
msg.header.frame_id = "imu_link"
msg.linear_acceleration.z = 9.81  # gravity
msg.angular_velocity.x = 0.0
# Set covariance[0] = -1 if orientation not provided
msg.orientation_covariance[0] = -1

sensor_msgs/LaserScan

2D LIDAR scan data.

code

std_msgs/Header header
float32 angle_min        # start angle [rad]
float32 angle_max        # end angle [rad]
float32 angle_increment  # angular step [rad]
float32 time_increment   # time between measurements [s]
float32 scan_time        # time for full scan [s]
float32 range_min        # minimum range [m]
float32 range_max        # maximum range [m]
float32[] ranges         # range data [m]
float32[] intensities    # intensity data (optional)

sensor_msgs/Image

Camera image data.

code

std_msgs/Header header
uint32 height            # image height (rows)
uint32 width             # image width (columns)
string encoding          # pixel encoding (rgb8, bgr8, mono8, etc.)
uint8 is_bigendian       # endianness
uint32 step              # row length in bytes
uint8[] data             # actual image data

Common encodings: rgb8, bgr8, rgba8, mono8, mono16, 32FC1

sensor_msgs/PointCloud2

3D point cloud data.

code

std_msgs/Header header
uint32 height
uint32 width
sensor_msgs/PointField[] fields
bool is_bigendian
uint32 point_step        # bytes per point
uint32 row_step          # bytes per row
uint8[] data
bool is_dense            # true if no invalid points

sensor_msgs/NavSatFix

GPS/GNSS data.

code

std_msgs/Header header
sensor_msgs/NavSatStatus status
float64 latitude         # degrees
float64 longitude        # degrees
float64 altitude         # meters above ellipsoid
float64[9] position_covariance
uint8 position_covariance_type

sensor_msgs/JointState

Robot joint state.

code

std_msgs/Header header
string[] name            # joint names
float64[] position       # radians or meters
float64[] velocity       # rad/s or m/s
float64[] effort         # Nm or N

geometry_msgs - Geometric Primitives

geometry_msgs/Twist

Velocity in free space (linear + angular).

code

geometry_msgs/Vector3 linear
  float64 x, y, z        # m/s
geometry_msgs/Vector3 angular
  float64 x, y, z        # rad/s

Usage: Robot velocity commands, typically on /cmd_vel.

Example - Sending velocity command:

python

from geometry_msgs.msg import Twist
cmd = Twist()
cmd.linear.x = 0.5   # forward 0.5 m/s
cmd.angular.z = 0.1  # rotate 0.1 rad/s
pub.publish(cmd)

geometry_msgs/Pose

Position + orientation in 3D.

code

geometry_msgs/Point position
  float64 x, y, z        # meters
geometry_msgs/Quaternion orientation
  float64 x, y, z, w     # quaternion

geometry_msgs/PoseStamped

Pose with header (timestamped and framed).

code

std_msgs/Header header
geometry_msgs/Pose pose

geometry_msgs/Transform

Coordinate frame transformation.

code

geometry_msgs/Vector3 translation
  float64 x, y, z        # meters
geometry_msgs/Quaternion rotation
  float64 x, y, z, w     # quaternion

geometry_msgs/TransformStamped

Stamped transform with parent/child frames.

code

std_msgs/Header header
string child_frame_id
geometry_msgs/Transform transform

geometry_msgs/Wrench

Force/torque in free space.

code

geometry_msgs/Vector3 force
  float64 x, y, z        # Newtons
geometry_msgs/Vector3 torque
  float64 x, y, z        # Newton-meters

nav_msgs - Navigation Messages

nav_msgs/Odometry

Robot odometry (pose + velocity estimate).

code

std_msgs/Header header
string child_frame_id
geometry_msgs/PoseWithCovariance pose
  geometry_msgs/Pose pose
  float64[36] covariance   # 6x6 pose covariance
geometry_msgs/TwistWithCovariance twist
  geometry_msgs/Twist twist
  float64[36] covariance   # 6x6 velocity covariance

nav_msgs/Path

Planned path (sequence of poses).

code

std_msgs/Header header
geometry_msgs/PoseStamped[] poses

nav_msgs/OccupancyGrid

2D occupancy map.

code

std_msgs/Header header
nav_msgs/MapMetaData info
  time map_load_time
  float32 resolution      # meters/cell
  uint32 width, height    # cells
  geometry_msgs/Pose origin
int8[] data              # occupancy: 0=free, 100=occupied, -1=unknown

std_msgs - Standard Primitives

std_msgs/Header

Standard message header.

code

uint32 seq               # sequence ID
time stamp               # timestamp
string frame_id          # coordinate frame

Common Types

Type	Description
Bool	true/false
Int8, Int16, Int32, Int64	Signed integers
UInt8, UInt16, UInt32, UInt64	Unsigned integers
Float32, Float64	Floating point
String	UTF-8 string
Time	ROS time (secs + nsecs)
Duration	ROS duration
Empty	Empty message (for triggers)

Unit Conventions

Quantity	Unit	Notes
Linear distance	meters	Always SI
Angular distance	radians	Not degrees
Linear velocity	m/s
Angular velocity	rad/s
Linear acceleration	m/s^2
Force	Newtons (N)
Torque	Newton-meters (Nm)
Time	seconds.nanoseconds	ROS Time format
Temperature	Kelvin or Celsius	Depends on message

Covariance Matrices

Many messages include covariance as a flat array:

•6x6 matrices (pose): 36 elements, row-major
•3x3 matrices (3D vector): 9 elements, row-major

Index mapping for 3x3:

code

[0  1  2 ]   [xx xy xz]
[3  4  5 ] = [yx yy yz]
[6  7  8 ]   [zx zy zz]

Unknown covariance: Set all to 0 Data not available: Set [0] to -1