ROS2 equivalent of ros::package::getPath

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The closest equivalent to what ros::package::getPath() returns in ROS 1 is what we call the package's "share directory", which is essentially the package's "install prefix" plus a standard (FHS based) relative path of share/<package name>. This is where we put the package.xml and where you should install architecture independent resources like images, launch files, config files, etc...

So, as an example, if your package is called foo and you installed to /home/user/my_ros2_ws/install, then the package share directory would be /home/user/my_ros2_ws/install/share/foo. But to get to that path you need to know (at runtime) where the package was installed to.

In ROS 2 this information is provided by the resource index:

https://github.com/ament/ament_cmake/...

This index is populated at compile time (rather then by crawling the filesystem at runtime as in ROS 1).

This index can be queried in various ways, but it can be used to get the installation prefix of a package (i.e. something like /opt/ros/ardent/ or ~/my_ros2_ws/install/), if it is installed on the system. Once you know that you can easily add the relative share directory path to the install prefix yourself. However, there are convenience API's in both C++ and Python to get the "share directory" of a package directly:

Python

API:

https://github.com/ament/ament_index/...

Example:

from ament_index_python.packages import get_package_share_directory
# may raise PackageNotFoundError
package_share_directory = get_package_share_directory('my_package_name')

C++

API:

https://github.com/ament/ament_index/...

Example:

#include <ament_index_cpp/get_package_share_directory.hpp>
// may throw ament_index_cpp::PackageNotFoundError exception
std::string package_share_directory = ament_index_cpp::get_package_share_directory("my_package_name");

Command-line

With the command line you can only get the package install prefix right now, but it would be simple to add the share directory as well.

Docs (only in -h for now):

% ros2 pkg prefix -h
usage: ros2 pkg prefix [-h] package_name

Output the prefix path of a package

positional arguments:
  package_name  The package name

optional arguments:
  -h, --help    show this help message and exit

Example:

% ros2 pkg prefix rclcpp
/Users/william/ros2_ws/install_debug

I made an issue to add the share directory to the command line tool, help welcome :)

https://github.com/ros2/ros2cli/issue...