Cool project.
I have tried using both wifi and IMU motion sensors for mapping indoor and it's not really that impressive yet. This is still a very hard problem to solve.
Google seems to be working on it: https://www.google.com/atap/project-tango/
For now, External distance cameras (Kinect-like) seems to be the most accurate and usable method. Something like what these quadcopters use: https://www.youtube.com/watch?v=AiCFtmdrvHM
There have also been many other projects like http://wearnotch.com/
For now, External distance cameras (Kinect-like) seems to be the most accurate and usable method. Something like what these quadcopters use: https://www.youtube.com/watch?v=AiCFtmdrvHM