Category: Robot Operating System (ROS)

ROS launch is a very useful command as it is capable to: run multiple nodes at the same time. set parameters. perform rosparam commands. set execution options. ROS launch file (.launch) is an XML file which looks like below. As it is an XML, indentation matters. An example launch file that sets a parameter: In …

ROS bag is used to record ROS messages and afterwards they can be played. This is very useful to record ROS messages published by robot’s sensors in a real test and later this data can be played without a need to perform another real test. Hence, this is particularly useful when the robot programming needs …

There are three types of messages in ROS: msg : used in topic srv : used in service action : used in action The msg message is defined in an .msg file, which looks like this: data_type variable_1 data_type variable_2 One or more .msg files are typically created inside a folder called “msg”. ROS topic …

ROS parameters are parameters in a node which can be modified from their default values. By this definition, the ROS parameters are very useful to be used when we want to be able to modify them quickly, in real-time. ROS parameters can be, for example, USB port numbers, camera calibration parameters, or minimum and maximum …

Below are the steps to create a ROS1 action: Step 1: Add the following in package.xml roscpp # Use this if the action is in C++ rospy # Use this if the action is in Python actionlib std_msgs message_generation actionlib_msgs roscpp # Use this if the action is in C++ rospy # Use this if …

Different from ROS service which consists of request and response only, ROS action additionally provides feedback. An action consists off three main parts: request, feedback, and result (which is similar to response in service). While a service is appropriate to be used for a non-progressive task, an action is appropriate to be used for a …

The following are some steps to create a ROS1 service in Python: Step 1: Add the following in package.xml rospy std_msgs message_generation rospy std_msgs message_runtime Step 2: Add the following in CMakeLists.txt find_package(catkin REQUIRED COMPONENTS message_generation std_msgs rospy) add_service_files(FILES ServiceName.srv) generate_messages(DEPENDENCIES std_msgs) catkin_package( LIBRARIES package_name CATKIN_DEPENDS std_msgs rospy ) catkin_install_python(PROGRAMS script/service_server.py DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION} ) catkin_install_python(PROGRAMS …

The following are some steps to create a ROS1 service in C++: Step 1: Add the following in package.xml roscpp std_msgs message_generation roscpp std_msgs message_runtime Step 2: Add the following in CMakeLists.txt find_package(catkin REQUIRED COMPONENTS message_generation std_msgs roscpp) add_service_files(FILES ServiceName.srv) generate_messages(DEPENDENCIES std_msgs) catkin_package( LIBRARIES package_name CATKIN_DEPENDS std_msgs roscpp ) include_directories(${catkin_INCLUDE_DIRS}) add_executable(service_server src/service_server.cpp) add_dependencies(service_server ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS}) …

Different from topic, service is bidirectional communication between a service server and a service client. The service can be described as the following sequential mechanism: A service client makes a request to a service server The service server sends a response to the service client The communication between the service client and the service server …

In ROS, a node can publish a topic and subscribe (listen) to a topic. A topic is basically a unidirectional message in a certain data type containing some information. It is like a radio broadcast. The radio station is the topic publisher whereas the radio receiver is the topic subscriber. The topic is the radio …