The <group> tag
The <group> tag makes it easier to apply settings to a group of nodes. It has an ns attribute that lets you push the group of nodes into a separate namespace. You can also use the <remap> tag to apply remap setting across the group.
- Assign the group of nodes to the specified namespace. The namespace can be global or relative, though global namespaces are discouraged.
Delete all parameters in the group's namespace before launch. This feature is very dangerous and should be used with caution. ns must be specified.
The <group> tag is equivalent to the top-level <launch> tag and simply acts as a container for the tags within. This means that you can use any tag as you would normally use it within a <launch> tag.
- Launch a node.
Set a parameter on the Parameter Server
- Declare a name remapping.
- Declare a machine to use for launching.
Set ROS parameters for the launch using a rosparam file.
Include other roslaunch files.
- Specify an environment variable for launched nodes.
Launch a test node (see rostest).
- Declare an argument.