2. Getting Started

2.1. Pre-requisites

Before you can start compiling the SlicerROS2 module, you will need:

  • Some knowledge of Linux, CMake and ROS 2.

  • Ubuntu Linux with ROS 2. This module has been developed and tested using Ubuntu 20.04 with ROS Galactic. It might also work on Ubuntu 22.04 with ROS Humble.

  • Slicer 3D built from source is required to build an extension.

    • Ubuntu 20.04 only. Instructions from the Slicer site recommend to install a newer version of Qt on Ubuntu 20.04. This makes the builds with ROS2 quite difficult so instead, we recommend to use Slicer versions up to 5.2.2 and use the Qt libraries installed by default along Ubuntu. After you cloned the Slicer sources, make sure you checkout 5.2.2 using git checkout v5.2.2.

    • Before you start compiling Slicer, make sure we use the system/native OpenSSL libraries otherwise you’ll get some errors when compiling the Slicer ROS 2 module. You will need to do the following after you ran CMake for the first time. In the Slicer build directory, set Slicer_USE_SYSTEM_OpenSLL to ON using cmake . -DSlicer_USE_SYSTEM_OpenSSL=ON -DCMAKE_BUILD_TYPE=Release or ccmake.

    See Slicer build instructions.

  • Remember the build directory for Slicer, it will be needed to compile the Slicer ROS 2 module.

Note

If you need to build Slicer from old sources, make sure CMAKE_CXX_STANDARD is set to 14 (required to compile Slicer code along ROS 2).

2.2. Compilation

This code should be built with colcon as a ROS 2 package. colcon is usually installed along ROS 2 but if it isn’t, install it with sudo apt install python3-colcon-common-extensions. For now, we will assume the ROS workspace directory is ~/ros2_ws and the source code for this module has been cloned under ~/ros2_ws/src/slicer_ros2_module.

You will first need to “source” the ROS setup script for ROS 2 (Galactic in this example):

source /opt/ros/galactic/setup.bash
mkdir -p ~/ros2_ws/src
cd ~/ros2_ws/src
git clone https://github.com/rosmed/slicer_ros2_module

Then build the module using colcon while providing the path to your Slicer build directory Slicer_DIR:

cd ~/ros2_ws
colcon build --cmake-args -DSlicer_DIR:PATH=/home/your_user_name_here/something_something/Slicer-SuperBuild-Debug/Slicer-build -DCMAKE_BUILD_TYPE=Release

The option --cmake-args -DSlicer_DIR... is only needed for the first colcon call. For future builds, you can revert back to just using colcon build.

Note that the build directory name is ROS2, not slicer_ros2_module. You will see some CMake warnings mentioning that the module’s name (ROS2) doesn’t follow the ROS2 package naming convention. ROS2 expects all packages to use the “snake_case” naming convention but we decided to ignore this to follow the VTK/Slicer naming convention, i.e. “CamelCase”.

If the Slicer_DIR is not set properly (or you simply forgot), you should see the following error messages”

Could not find a package configuration file provided by "Slicer" with any
of the following names:

SlicerConfig.cmake
slicer-config.cmake

At that point, you don’t need to clean your ROS workspace. You can fix the issue by running CMake on the build directory for the Slicer module (ROS2) ccmake ~/ros2_ws/build/ROS2. In CMake, set Slicer_DIR to point to your Slicer build directory then hit c to configure until you can hit g to generate the makefiles. If you prefer a graphical interface, you can use cmake-gui instead of ccmake. Once Slicer_DIR is set, try colcon build again (after cd ~/ros2_ws).

2.3. Loading the module

You will first need to make sure the environment variables are set properly so the Slicer ROS 2 module can locate all the ROS 2 resources (dynamic libraries and other ROS 2 packages you might need to access):

source ~/ros2_ws/install/setup.bash # or whatever your ROS 2 workspace is

In the same terminal navigate (cd) to your Slicer inner build directory and start Slicer. If you followed the Slicer build instructions, this should look like:

cd ~/something_something/Slicer-SuperBuild/Slicer-build
./Slicer

The first time you run Slicer, you need to add the module directory in the application settings so that the module can be dynamically loaded.

To do so, open Slicer and navigate through the menus: Edit → Application Settings → Modules → Additional module paths → Add. The path to add is based on your ROS workspace location as well as the Slicer version (5.3 in this example). It should look like:

~ros2_ws/build/ROS2/lib/Slicer-5.3/qt-loadable-modules

At that point, Slicer will offer to restart. Do so and then load the module using the drop down menu: Modules → IGT → ROS2