Is Iteration Worth It? Revisit its Impact in Sliding-Window VIO

Visual-inertial odometry (VIO), which fuses noisy inertial readings and camera measurements to provide 3D motion tracking, is a foundational component in many autonomous applications. With the increasing use of next-generation edge devices (e.g., AR/VR devices, nano drones, and mobile robotics) that are constrained by limited power, resources, and multitasking demands, balancing computational efficiency and accuracy in VIO estimators has become more critical than ever. Historically, state estimation algorithms have been developed using either optimization or filtering-based methods, with the key distinction being the ability to relinearize measurements and correct state estimates iteratively. It has been widely claimed that iterative methods improve accuracy by allowing for the reduction of error through relinearization at a higher computational demand. Conversely, filtering methods are more efficient but may suffer from significant linearization errors. However, these trade-offs have not been thoroughly examined in the context of visual-inertial motion tracking. In this paper, we conduct the first comprehensive study on the impact of iterative algorithms in sliding-window VIO. We analyze the relinearization of IMU and camera measurements separately, providing insights into how each affects system performance. By considering key factors such as system observability and measurement processes, we offer a deeper understanding of VIO estimator behavior. Our findings, backed by real-world tests, offer practical guidelines for balancing accuracy and efficiency, helping practitioners determine when to prioritize iterative methods or simpler filtering approaches while encouraging researchers and engineers to rethink VIO design for optimal resource allocation.