autoware_auto_tf2

This is the design document for the autoware_auto_tf2 package.

Purpose / Use cases

In general, users of ROS rely on tf (and its successor, tf2) for publishing and utilizing coordinate frame transforms. This is true even to the extent that the tf2 contains the packages tf2_geometry_msgs and tf2_sensor_msgs which allow for easy conversion to and from the message types defined in geometry_msgs and sensor_msgs, respectively. However, AutowareAuto contains some specialized message types which are not transformable between frames using the ROS2 library. The autoware_auto_tf2 package aims to provide developers with tools to transform applicable autoware_auto_msgs types. In addition to this, this package also provides transform tools for messages types in geometry_msgs missing in tf2_geometry_msgs.

Design

While writing tf2_some_msgs or contributing to tf2_geometry_msgs, compatibility and design intent was ensured with the following files in the existing tf2 framework:

• tf2/convert.h
• tf2_ros/buffer_interface.h

For example:

void tf2::convert( const A & a,B & b)

The method tf2::convert is dependent on the following:

template<typename A, typename B>
  B tf2::toMsg(const A& a);
template<typename A, typename B>
  void tf2::fromMsg(const A&, B& b);
 
// New way to transform instead of using tf2::doTransform() directly
tf2_ros::BufferInterface::transform(...)

Which, in turn, is dependent on the following:

void tf2::convert( const A & a,B & b)
const std::string& tf2::getFrameId(const T& t)
const ros::Time& tf2::getTimestamp(const T& t);

Current Implementation of tf2_geometry_msgs

In both ROS1 and ROS2 stamped msgs like Vector3Stamped, QuaternionStamped have associated functions like:

• getTimestamp
• getFrameId
• doTransform
• toMsg
• fromMsg

In ROS1, to support tf2::convert and need in doTransform of the stamped data, non-stamped underlying data like Vector3, Point, have implementations of the following functions:

• toMsg
• fromMsg

In ROS2, much of the doTransform method is not using toMsg and fromMsg as data types from tf2 are not used. Instead doTransform is done using KDL, thus functions relating to underlying data were not added; such as Vector3, Point, or ported in this commit ros/geometry2/commit/6f2a82. The non-stamped data with toMsg and fromMsg are Quaternion, Transform. Pose has the modified toMsg and not used by PoseStamped.

Plan for autoware_auto_msgs::msg::BoundingBoxArray

The initial rough plan was to implement some of the common tf2 functions like toMsg, fromMsg, and doTransform, as needed for all the underlying data types in BoundingBoxArray. Examples of the data types include: BoundingBox, Quaternion32, and Point32. In addition, the implementation should be done such that upstream contributions could also be made to geometry_msgs.

Assumptions / Known limits

Due to conflicts in a function signatures, the predefined template of convert.h/ transform_functions.h is not followed and compatibility with tf2::convert(..) is broken and toMsg is written differently.

// Old style
geometry_msgs::Vector3 toMsg(const tf2::Vector3& in)
geometry_msgs::Point& toMsg(const tf2::Vector3& in)
 
// New style
geometry_msgs::Point& toMsg(const tf2::Vector3& in, geometry_msgs::Point& out)

Inputs / Outputs / API

The library provides API doTransform for the following data-types that are either not available in tf2_geometry_msgs or the messages types are part of autoware_auto_msgs and are therefore custom and not inherently supported by any of the tf2 libraries. The following APIs are provided for the following data types:

• Point32

  inline void doTransform(
    const geometry_msgs::msg::Point32 & t_in,
    geometry_msgs::msg::Point32 & t_out,
    const geometry_msgs::msg::TransformStamped & transform)

• Quarternion32 (autoware_auto_msgs)

  inline void doTransform(
    const autoware_auto_msgs::msg::Quaternion32 & t_in,
    autoware_auto_msgs::msg::Quaternion32 & t_out,
    const geometry_msgs::msg::TransformStamped & transform)

• BoundingBox (autoware_auto_msgs)

  inline void doTransform(
    const BoundingBox & t_in, BoundingBox & t_out,
    const geometry_msgs::msg::TransformStamped & transform)

• BoundingBoxArray

  inline void doTransform(
    const BoundingBoxArray & t_in,
    BoundingBoxArray & t_out,
    const geometry_msgs::msg::TransformStamped & transform)

In addition, the following helper methods are also added:

• BoundingBoxArray

  inline tf2::TimePoint getTimestamp(const BoundingBoxArray & t)
   
  inline std::string getFrameId(const BoundingBoxArray & t)

Future extensions / Unimplemented parts

Challenges

• tf2_geometry_msgs does not implement doTransform for any non-stamped datatypes, but it is possible with the same function template. It is needed when transforming sub-data, with main data that does have a stamp and can call doTransform on the sub-data with the same transform. Is this a useful upstream contribution?
• tf2_geometry_msgs does not have Point, Point32, does not seem it needs one, also the implementation of non-standard toMsg would not help the convert.
• BoundingBox uses 32-bit float like Quaternion32 and Point32 to save space, as they are used repeatedly in BoundingBoxArray. While transforming is it better to convert to 64-bit Quaternion, Point, or PoseStamped, to re-use existing implementation of doTransform, or does it need to be implemented? Templatization may not be simple.