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Modern smartphones have all the sensing capabilities required for accurate and robust navigation and tracking. In specific environments some data streams may be absent, less reliable, or flat out wrong. In particular, the GNSS signal can become flawed or silent inside buildings or in streets with tall buildings. In this application paper, we aim to advance the current state-of-the-art in motion estimation using inertial measurements in combination with partial GNSS data on standard smartphones. We show how iterative estimation methods help refine the positioning path estimates in retrospective use cases that can cover both fixed-interval and fixed-lag scenarios. We compare estimation results provided by global iterated Kalman filtering methods to those of a visual-inertial tracking scheme (Apple ARKit). The practical applicability is demonstrated on real-world use cases on empirical data acquired from both smartphones and tablet devices.

One example path captured by an Apple iPad. (a) GNSS/platform location positions with uncertainty radius. The samples in green were removed for the gap experiment. (b) The visual-inertial odometry (Apple ARKit) track that was captured for reference/validation. The ARKit fuses information from the IMU and device camera. The path has been manually aligned to the starting point and orientation. (c) Our iterative solution of the gap experiment, where we fuse the iPad IMU readings with the blue GNSS locations in (a). Note that the lines straighten along the roads and the corners are square. (d) Example frames along the path showing the test environment. Associated camera poses shown in (b).

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