Abstract: In one embodiment, a technique for determining a position of a user inside of a structure is disclosed. Acceleration and orientation data is captured by an inertial motion unit (IMU) affixed to the user. Range data is captured by one or more range finders affixed to the user. An estimate of the user's relative displacement is produced based on the acceleration and orientation data captured by the IMU. A cloud of particles is generated within a model of the structure based on the estimated relative displacement. One or more particle filters are applied to the cloud of particles to eliminate any particles of the cloud of particles that violate physical constraints and to eliminate any particles of the cloud of particles that are inconsistent with the range data. Then a statistical function is applied to the cloud of particles to determine a calculated position of the user.