This repo contains an official implementation of MegBA.

MegBA is a fast and distributed library for large-scale Bundle Adjustment (BA). MegBA has a novel end-to-end vectorised BA algorithm which can fully exploit the massive parallel cores on GPUs, thus speeding up the entire BA computation. It also has a novel distributed BA algorithm that can automatically partition BA problems, and solve BA sub-problems using distributed GPUs. The GPUs synchronise intermediate solving state using network-efficient collective communication, and the synchronisation is designed to minimise communication cost. MegBA has a memory-efficient GPU runtime and it exposes g2o-compatible APIs. Experiments show that MegBA can out-perform state-of-the-art BA libraries (i.e., Ceres and DeepLM) by ~50x and ~5x respectively, in public large-scale BA benchmarks.

• 2021/12/06 Beta version released! It corresponds to this paper
• 2022/02/18 Stable version released! We have refactored MegBA and fixed some existing bugs, e.g., incorrect rollback in the LM reject step.
• 2022/02/25 Analytical differentiation module available; We also provide BAL_X_analytical.cpp under examples/. Compared with automatic diff, time and space are reduced by ~30% and ~40%, respectively.

• memory-efficient version with implicit Hessian (TBD)
• IMU factor, prior factor (TBD)

Paper: https://arxiv.org/abs/2112.01349 (updated version)

Dependencies:

• C++14
• CMake (>= 3.15)
• CUDA (>= 11.2)
• gflags
• NCCL2 (if you need Distributed features) https://developer.nvidia.com/nccl/nccl-download

You can also easily install all dependencies with script: script

Demo with BAL dataset:

• Download any pre.txt.bz2 file from BAL Dataset: https://grail.cs.washington.edu/projects/bal/ and uncompressed.

• Compile

  If you want to use the distributed feature, use cmake -DMEGBA_ENABLE_NCCL .. instead of cmake ...

  git submodule update --init
  mkdir build
  cd build
  cmake ..  # enable nccl by using cmake -DMEGBA_ENABLE_NCCL ..
  make -j4 BAL_Double

• Run the demo (Venice-1778)

  cd examples
  ./BAL_Double --path /path/to/your/dataset --world_size 2 --max_iter 100 --solver_tol 1e-1 --solver_refuse_ratio 1 --solver_max_iter 100 --tau 1e4 --epsilon1 1 --epsilon2 1e-10

  • world_size: number of GPUs available
  • max_iter: the maximal number of LM iteration
  • epsilon1 & epsilon2: threshold in LM
  • solver_tol: tolerance of solver (distributed PCG solver)
  • solver_refuse_ratio: early stop for the solver
  • solver_max_iter: the maximal iteration of solver
  • tau: the initial region

• Currently, MegBA implements automatic differentiation only for generalizability. Please consider implementing your own analytical differentiation module. Analytical differentiation module is provided.
• If you use devices without modern inter-device communication (i.e., NVLinks..), you might find the data transfer is the bottleneck.
• Empirically, we found it is necessary to customize the LM trust-region strategies and tune its hyper-parameters to further boost the performance.

Under doc/ (Coming soon...)

Please check here for MegBA's future plan.

If you are interested in MegBA and want to collaborate, you can:

• Sorry, we can no longer host Interns.
• As an external collaborator (coding), just fork this repo and send PRs. We will review your PR carefully (and merge it into MegBA).
• As an algorithm/novelty contributor, please send an email to MegBA@googlegroups.com.
• Any new feature request, you can send an email to MegBA@googlegroups.com as well. Note that it is not guaranteed the requested feature will be added or added soon

Contact Information:

• Jie Ren jieren9806@gmail.com
• Wenteng Liang wenteng_liang@163.com
• Ran Yan yanran@megvii.com
• Shiwen Liu lswbblue@163.com
• Xiao Liu liuxiao@foxmail.com

If you find MegBA useful for your project, please consider citing:

@inproceedings{2021megba,
  title={MegBA: A GPU-Based Distributed Library for Large-Scale Bundle Adjustment}, 
  author={Jie Ren and Wenteng Liang and Ran Yan and Luo Mai and Shiwen Liu and Xiao Liu},
  booktitle={European Conference on Computer Vision},
  year={2022}
}

MegBA is licensed under the Apache License, Version 2.0.