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tf_transformations library

ROS / ros world / ros tf

tf_transformations is a Python utility library in ROS that provides functions for working with 3D rotations and transformations. converting between different orientation formats like Euler angles, quaternions, and transformation matrices.

install
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sudo apt install ros-$ROS_DISTRO-tf-transformations

Quaternion <-> Euler

  • quaternion_from_euler
  • euler_from_quaternion
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from tf_transformations import quaternion_from_euler, euler_from_quaternion
import math

# euler default axis rpy ("sxyz")
# quaternion [x, y, z, w]
q = quaternion_from_euler(0, 0, math.pi/2)
roll, pitch, yaw = euler_from_quaternion([x, y, z, w])

Rotation Axes

Euler angles describe a 3D rotation as a sequence of three rotations around three orthogonal axes. the axes parameter is 4 character string, defines the specific convention of Euler angles you are using.

Static (Extrinsic) Rotations
  • Character: The axes string starts with 's'.
  • Description: Each rotation is performed about a fixed, global coordinate system's axes. The axes do not move with the object.
Rotating (Intrinsic) Rotations
  • Character: The axes string starts with 'r'.
  • Description: Each rotation is performed about the object's own moving coordinate system's axes. The axes change their orientation after each preceding rotation.
Common Conventions

Roll-Pith-Yaw (RPY)

  • Roll: Rotation around the X-axis
  • Pitch: Rotation around the Y-axis
  • Yaw: Rotation around the Z-axis
Extrinsic Rotating
alt text alt text
sxyz rxyz
quaternion = quaternion_from_euler(yaw_rad, pitch_rad, roll_rad, axes='sxyz') quaternion = quaternion_from_euler(yaw_rad, pitch_rad, roll_rad, axes='rxyz')

quaternion_about_axis

This function creates a quaternion that represents a rotation around a single axis by a given angle.

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import tf_transformations
import numpy as np

angle = np.radians(90)
axis = [1, 0, 0]  # X axis

q = tf_transformations.quaternion_about_axis(angle, axis)
print("Quaternion:", q)