  As the current initialization method in the state-of-the-art Stereo
Visual-Inertial SLAM framework, ORB-SLAM3 has limitations. Its success depends
on the performance of the pure stereo SLAM system and is based on the
underlying assumption that pure visual SLAM can accurately estimate the camera
trajectory, which is essential for inertial parameter estimation. Meanwhile,
the further improved initialization method for ORB-SLAM3, known as Stereo-NEC,
is time-consuming due to applying keypoint tracking to estimate gyroscope bias
with normal epipolar constraints. To address the limitations of previous
methods, this paper proposes a method aimed at enhancing translation accuracy
during the initialization stage. The fundamental concept of our method is to
improve the translation estimate with a 3 Degree-of-Freedom (DoF) Bundle
Adjustment (BA), independently, while the rotation estimate is fixed, instead
of using ORB-SLAM3's 6-DoF BA. Additionally, the rotation estimate will be
updated by considering IMU measurements and gyroscope bias, unlike ORB-SLAM3's
rotation, which is directly obtained from stereo visual odometry and may yield
inferior results when operating in challenging scenarios. We also conduct
extensive evaluations on the public benchmark, the EuRoC dataset, demonstrating
that our method excels in accuracy.
