Nodes

The SlicerROS2 module always creates a default ROS node (internally a rclcpp::node). This node is both a ROS node and a MRML node, hence the unfortunate name vtkMRMLROS2NodeNode. This node is added to the MRML scene and should be used to add your custom vtkMRMLROS2 nodes (topics, parameter…). It is possible to add more ROS nodes in SlicerROS2 but this feature has not been tested extensively for the first release.

To retrieve the default ROS node:

rosLogic = slicer.util.getModuleLogic('ROS2')
rosNode = rosLogic.GetDefaultROS2Node()

If you’re modifying the Slicer ROS module, you can access the default ROS node directly using the GetDefaultROS2Node method.

vtkMRMLROS2NodeNode * rosNode = this->GetDefaultROS2Node();

If you’re working on a new module that relies on the SlicerROS2 module, you can use the GetModuleLogic method and then the GetDefaultROS2Node.

vtkMRMLAbstractLogic * logic = this->GetModuleLogic("ROS2");
if (logic == nullptr) {
  vtkErrorMacro(<< "ROS 2 logic not found");
} else {
 vtkSlicerROS2Logic * rosLogic =
      vtkSlicerROS2Logic::SafeDownCast(logic);
  if (rosLogic == nullptr) {
    vtkErrorMacro(<< "Found what should be the default ROS 2 logic but the type is wrong");
  } else {
    vtkMRMLROS2NodeNode * rosNode = rosLogic->GetDefaultROS2Node();
    // now we can use the node
  }
}

For all other cases, you can use node ID of the default ROS node (vtkMRMLROS2NodeNode1) to retrieve it from the MRML scene.

vtkMRMLNode * node = scene->GetNodeByID("vtkMRMLROS2NodeNode1");
if (node == nullptr) {
  vtkErrorMacro(<< "ROS 2 default node not in scene");
} else {
  vtkMRMLROS2NodeNode * rosNode =
      vtkMRMLROS2NodeNode::SafeDownCast(node);
  if (rosNode == nullptr) {
    vtkErrorMacro(<< "Found what should be the default ROS 2 node but the type is wrong");
  } else {
    // now we can use the node
  }
}