Is this necessry to learn ros for ros 2?

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Theoretically it should not be required to learn ROS before diving into ROS2, but I would strongly recommend it.

ROS2 is still quite new so there are not too many resources available that will teach you everything about ROS2 from the point of view of someone who does not know ROS.

This tutorial from Erle Robotics is one of the few that covers the basic of ROS2 without requiring ROS. http://docs.erlerobotics.com/robot_op...

However, it's definitely not as complete as the official ROS tutorial http://wiki.ros.org/

Note that from the user application point of view, most of the basic concepts are the same between ROS and ROS2. At a first glance it may appear that only the APIs have changed (even if also the recommended design patterns are). For this reason, given the current state of ROS2 (perfectly working, but under heavy development) also the official ROS2 tutorials focus only on highlighting the differences between ROS and ROS2. https://index.ros.org/doc/ros2/Tutori...