I've never worked on Mecanum wheels before so I researched a bit. One of the first things I look for is there has to be a way to combine all of the encoder velocity measurements. Apparently, Jacobian equation can be used for that (I believe it is H_encoder in your question).
You can calculate system's velocity by
Usually, robot's float a topic (eg /mobile_base/commands/reset_odometry for TurtleBot) to reset the odometry.
The URDF for the Rosbot2.0 uses Skid Steer plugin. This plugin does not expose a method for resetting the odometry of the robot. So you can't reset odometry by calling a topic or from launch file.
But nothing stops you from internally keeping track ...