Tightly Coupled Visual-Inertial-UWB Indoor Localization System With Multiple Position-Unknown Anchors

In this letter, we perform a tightly-coupled fusion of a monocular camera, a 6-DoF IMU, and multiple position-unknown Ultra-wideband (UWB) anchors to construct an indoor localization system with both accuracy and robustness. Prior to this, there have been several works that have achieved satisfactory results by fusing UWB ranging measurements with visual-inertial system. However, these approaches still have some limitations: 1) these approaches either require the UWB anchor position to be calibrated in advance or the UWB anchor position estimation method used is not robust enough; 2) these approaches do not allow for dynamic changes to the number of UWB anchors in a tightly coupled estimator. Our approach uses visual object detection algorithm to provide UWB anchor initial position and refine it in the factor graph, using chi-square test algorithm to identify UWB ranging outliers. Based on the above two ideas, we implement a tightly coupled estimator that dynamically adjusts the number of UWB anchors, i.e. adding them to the factor graph when their ranging measurements are available and discarding them when their ranging measurements are outliers. These ideas improve the efficiency and robustness of the fusion about UWB ranging measurements with the visual-inertial system, as well as the easy setup of UWB anchors. Experimental results show that the proposed method outperforms previous methods in terms of estimating anchor position and improving localization accuracy.