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1. Names

1.1 Graph Resource Names

Graph Resource Names provide a hierarchical naming structure that is used for all resources in a ROS Computation Graph, such as:

  • Nodes
  • Parameters
  • Topics
  • Services

1.1.1 Resolving Name

There are four types of Graph Resource Names in ROS with the following syntax

  • base
  • relative/name
  • /global/name
  • ~private/name

1.2 Package Resource Names

Package Resource Names are used in ROS with Filesystem-Level concepts to simplify the process of referring to files and data types on disk. Examples:

  • Message (msg) types. For example, the name "std_msgs/String" refers to the "String" message type in the "std_msgs" Package.
  • Service (srv) types
  • Node types

2. Remapping Arguments

Any Graph Resource Names within a node can be remapped when it is launched at the command-line, This lets you launch the same node with multiple configurations from the command-line. syntax is name:=new_name

This will remap the topic chat to chatter

rosrun tutorials talker  chat:=/chatter

remapping so that the new node ends up subscribing to /needed_topic when it thinks it is subscribing to /different_topic

<remap from="/different_topic" to="/needed_topic"/>

Refs: 1

3. Special keys

  • __name: name of the node
  • __log: designates the location that the node's log file
  • __ip: and __hostname: substitutes for ROS_IP and ROS_HOSTNAME.
  • __master: substitute for ROS_MASTER_URI.
  • __ns: substitute for ROS_NAMESPACE. The ROS_NAMESPACE lets you push down a Node into a namespace. All of the names in the Node will be resolved relative to this value, including remapped names.

Example: This let you launch robot1 and robot2 start sedning their message (i.e. their position)

rosrun tutorials talker  __ns:=robot1  
rosrun tutorials talker  __ns:=robot2

rosrun tutorials listener __ns:=robot1
rosrun tutorials listener __ns:=robot2

or you can run a node in a namespace, simply add the ns attribute to a tag. For example

<node pkg="foo" type="bar" name="my_node" ns="my_namespace" />

Refs: 1

NodeHandles

  1. public: /namespace/topic
ros::NodeHandle nh=ros::NodeHandle();

This will look for your parameter in the global namespace,it will find /my_param

  1. private: /namespace/node/topic
ros::NodeHandle nh=ros::NodeHandle("~my_private_namespace");

This will look under the nested namespaces of the node itself and will find /namespace/my_node_name/my_param.

  1. namespaced: /namespace/node/topic
ros::NodeHandle nh=ros::NodeHandle("my_namespace");
  1. global: /topic
ros::NodeHandle nh=ros::NodeHandle("/my_global_namespace");

Refs: 1, 2, 3

Publishers and Subscribers

Refs: 1

Roslaunch

roslaunch tutorials display.launch model:=urdf/01-myfirst.urdf

URDF

urdf tutorial

Refs: 1

rosrun xacro xacro path/to/file.xacro > model.urdf

check_urdf model.urdf

Frames are attached to the links. Every link has an origin located in its center of mass which is called **link origin **. For instance for a cylinder it is in the center of that. Visual, inertia and collision can have offset relative to that. If a link is child of a joint, the **link origin ** is the ** joint origin **. joint origin is its parent link origin.

For instance here we have right_leg

    <link name="right_leg">
        <visual>
            <geometry>
                <box size="0.6 0.1 0.2"/>
            </geometry>
            <origin rpy="0 0 0" xyz="1 0 0"/>
        </visual>
    </link>

and

    <joint name="base_to_right_leg" type="fixed">
        <parent link="base_link"/>
        <child link="right_leg"/>
        <origin rpy="0 0 0" xyz="0 1 1"/>
    </joint>







roslaunch tutorials complete_model.launch

Refs: 1, 2, 3 , 4

Publishing the State

Refs: 1, 2

Differential Drive Wheel Systems

Refs: 1, 2

ROS best practices

Refs: 1, 2

move_base

Refs: 1

ROS Odometery Model

Refs: 1, 2, 3

ROS State Estimation

Refs: 1, 2, 3, 4, 5, 6

tf2 with ROS

ROS1

rosrun tf static_transform_publisher x y z qx qy qz qw parent_frame child_frame period_in_ms

ROS2

ros2 run tf2_ros static_transform_publisher 1 2 3 0.5 0.1 -1.0 <parent-frame> <child-frame>

Refs: 1

EKF Implementations

Refs: 1, 2

Filtering ROS bag

To extract a part of a ROS bag:

rosbag filter example.bag sliced.bag "t.secs >= 1702474496 and t.secs <= 1702474660"

Representing Robot Pose

Refs: 1

catkin

always call catkin_make in the root of your catkin workspace

cd ~/catkin_ws
catkin_make

The above command will build any packages located in ~/catkin_ws/src. The equivalent commands to do this manually would be:

 cd ~/catkin_ws
 cd src
 catkin_init_workspace
 cd ..
 mkdir build
 cd build
 cmake ../src -DCMAKE_INSTALL_PREFIX=../install -DCATKIN_DEVEL_PREFIX=../devel
 make

Refs: 1

Docker Installation

docker pull osrf/ros:noetic-desktop-full

allow GUI

export containerId=$(docker ps -l -q)

and

xhost +local: docker inspect --format='{{ .Config.Hostname }}' $containerId

then:

docker run -it --privileged \
  --env=LOCAL_USER_ID="$(id -u)" \
  -v /home/behnam:/home/behnam:rw \
  -v /tmp/.X11-unix:/tmp/.X11-unix:ro \
  -e DISPLAY=$DISPLAY \
  --network host \
  --name=ros1 osrf/ros:noetic-desktop-full