π-BA: Bundle Adjustment Hardware Accelerator based on Distribution of 3D-Point Observations

Abstract

Bundle adjustment (BA) is a fundamental optimization technique used in many crucial applications, including 3D scene reconstruction, robotic localization, camera calibration, autonomous driving, street view map generation, and even space exploration etc. Essentially, BA is a joint non-linear optimization problem, and one which can consume a significant amount of time and power, especially for large optimization problems. Previous approaches of optimizing BA performance heavily rely on parallel processing or distributed computing, which trade higher power consumption for higher performance. In this article we propose $\pi$ π -BA, the first hardware-software co-designed BA hardware accelerator that exploits custom hardware to simultaneously achieve higher performance and power efficiency. Specifically, based on our key observation that not all 3D points appear on all images in a BA problem, we designed a Co-Observation Optimization technique to accelerate BA operations with optimized usage of memory and computation resources. In addition, we developed a hardware-friendly differentiation method, which combines the analytic and forward automatic differentiation to calculate derivatives of projection function in the BA problem. We have implemented the proposed design on an embedded FPGA SoC, and experimental results confirm that $\pi$ π -BA outperforms the existing software implementations in terms of performance and power consumption.