Just found this website that includes a methodology to produce very accurate indoor navigation. They combine a technique called Rolling Shutter with IMU sensor fusion.
Here's the paper covering her methodology: http://www.ee.ucr.edu/~mourikis/papers/Li2013ICRA.pdf
Don't be intimidated by the quaternion math because Invensense solves them for us in the MPU 6050.
I haven't yet found the source code but will post it here when I do. Here's some source code from Hannes Ovren who is integrating Rolling Shutter with gyro data: github.com/hovren/crisp
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