Convert from Twist to orientation/heading

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I'm working on blending two headings and converting them into an 'ideal' heading for a Turtlebot. I would like to use the navigation stack's planner to get the optimal heading but it only provides me with the command velocities being sent.

Is there a way to convert the Twist messages being sent into Quaternion or Euler angles?

If not, is there a way to obtain the optimal heading from the navigation planner?