<slide_break></slide_break> ### Simulators * Software to allow work even without actual robots * For ROS they implement a series of nodes that pretend to be a robot * publish topics that a robot would publish (e.g. /odom) * Subscribe to topics that a robot would (e.g. /cmd_vel) * Uses a "physics engine" to simulate what would happen in the real world * Simulator creates the 3d world * Maintains an imaginary x,y where the robot is right now * Uses 3-d dynamic model of the robot * Has 3-d models of obstacles like walls * Changes all these states based on motion commands it receives * Of course, much more complex * Gazebo is a complete simulation environment * Really sophisticated 3d simulator plus visualization * Can simulate all kinds of things not just our robots * I have seen Gazebo models of a complete Amazon Warehouse Floor * With multiple Robots running around * RViz can only visualize data in 3D but it is not the source of the data * While it looks similar, it is not a simulator * It "simply" visualizes topics that it subscribes * In a 3-d space <div class="callout callout-small"> <span class="callout-badge">NB</span> We will NOT be using simulators called STAGE or STDR </div>