Gazebo plugins help us to control the robot models, sensors, world properties,
and even the way Gazebo runs. Similar to pluginlib and nodelets, Gazebo plugins are a set of C++ code, which can be dynamically loaded/unloaded from the Gazebo simulator.

Using plugins we can access all the components of Gazebo, and also it is independent of ROS, so that it can share with people who are not using ROS too.
We can mainly classify the plugins as follows:

• The world plugin: Using the world plugin, we can control the properties of a specific world in Gazebo. We can change the physics engine, the lighting, and other world properties using this plugin.
• The model plugin: The model plugin is attached to a specific model in Gazebo and controls its properties. The parameters such as joint state of the model, control of the joints, and so, on can be controlled using this plugin.
• The sensor plugin: The sensor plugins are for modeling sensors such as camera, IMU, and so on, in Gazebo.
• The system plugin: The system plugin is started along with the Gazebo startup. A user can control a system related function in Gazebo using
  this plugin.
• The visual plugin: The visual property of any Gazebo component can be accessed and controlled using the visual plugin.

Before starting development with Gazebo plugins, we might need to install some packages. If you are using ROS Indigo, the package we installed in the previous chapter is sufficient for developing Gazebo plugins. The Gazebo version installed along with ROS Indigo is 2.2.3. But if you are working with ROS Jade, the default Gazebo is Version 5, so you might need to install its development package in Ubuntu using the following command:

    $ sudo apt-get install libgazebo5-dev

The Gazebo plugins are independent of ROS and we don't need ROS libraries to build the plugin.