Navigate from unknown to known environment

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Just saying, if you want people to take the time to make a clear and complete answer,you should take the time to ask your question clearly. With the mistake in the first sentence and the formulation of your question, it took me more than 5minutes to really understand what you are asking for...

About your issue, in my opinion, you should make some research on odometry methods and find one adapted to your application. A SLAM method would allow you to map your previously unknown environnement but you don't need that much information, you just need to keep track on your position in your unknown environnement to be able to go back to your the known part of your world later. Odometry techniques will allow you to do so.