Apparatus and methods for displaying a three-dimensional model image of a portion of a target object. An imaging device is equipped with an inertial measurement unit (IMU) and a processor configured to execute a three-dimensional (3-D) visualization application. The IMU is used to track movement of the imaging device relative to a known initial location in a frame of reference of the target object. Imaging device position offsets are computed using relative position and orientation information acquired by a dead-reckoning process. The processor is configured to execute an algorithm that combines orientation data from the IMU with walking step information to produce a piecewise linear approximation for relative motion measurement. The resulting relative location data can then be used by the 3-D visualization application to provide an estimated 3-D viewpoint to display a 3-D model of a feature in the imaged area of interest.