Repository for our TIV 2023 paper "Occupancy-MAE: Self-supervised Pre-training Large-scale LiDAR Point Clouds with Masked Occupancy Autoencoders".

Mask-based pre-training has achieved great success for self-supervised learning in images and languages without manually annotated supervision. However, it has not yet been studied for large-scale point clouds with redundant spatial information. In this research, we propose a mask voxel autoencoder network for pre-training large-scale point clouds, dubbed Voxel-MAE. Our key idea is to transform the point clouds into voxel representations and classify whether the voxel contains point clouds. This simple but effective strategy makes the network voxel-aware of the object shape, thus improving the performance of downstream tasks, such as 3D object detection. Our Voxel-MAE, with even a 90% masking ratio, can still learn representative features for the high spatial redundancy of large-scale point clouds. We also validate the effectiveness of Voxel-MAE on unsupervised domain adaptative tasks, which proves the generalization ability of Voxel-MAE. Our Voxel-MAE proves that it is feasible to pre-train large-scale point clouds without data annotations to enhance the perception ability of the autonomous vehicle. Extensive experiments show great effectiveness of our pre-training method with 3D object detectors (SECOND, CenterPoint, and PV-RCNN) on three popular datasets (KITTI, Waymo, and nuScenes).

Flowchart of Voxel-MAE

Please refer to INSTALL.md for the installation of OpenPCDet(v0.5).

Please refer to GETTING_STARTED.md .

KITTI:

Train with multiple GPUs:
bash ./scripts/dist_train_voxel_mae.sh ${NUM_GPUS}  --cfg_file cfgs/kitti_models/voxel_mae_kitti.yaml --batch_size ${BATCH_SIZE}

Train with a single GPU:
python3 train_voxel_mae.py  --cfg_file cfgs/kitti_models/voxel_mae_kitti.yaml --batch_size ${BATCH_SIZE}

Waymo:

python3 train_voxel_mae.py  --cfg_file cfgs/kitti_models/voxel_mae_waymo.yaml --batch_size ${BATCH_SIZE}

nuScenes:

python3 train_voxel_mae.py  --cfg_file cfgs/kitti_models/voxel_mae_nuscenes.yaml --batch_size ${BATCH_SIZE}

Same as OpenPCDet with pre-trained model from our Voxel-MAE.

bash ./scripts/dist_train.sh ${NUM_GPUS}  --cfg_file cfgs/kitti_models/second.yaml --batch_size ${BATCH_SIZE} --pretrained_model ../output/kitti/voxel_mae/ckpt/check_point_10.pth

The results are the 3D detection performance of moderate difficulty on the val set of KITTI dataset. Results of OpenPCDet are from here .

Similar to OpenPCDet , all models are trained with a single frame of 20% data (~32k frames) of all the training samples , and the results of each cell here are mAP/mAPH calculated by the official Waymo evaluation metrics on the whole validation set (version 1.2).

Our codes are released under the Apache 2.0 license.

This repository is based on OpenPCDet.

If you find this project useful in your research, please consider cite:

@article{min2023occupancy,
  title={Occupancy-MAE: Self-Supervised Pre-Training Large-Scale LiDAR Point Clouds With Masked Occupancy Autoencoders},
  author={Min, Chen and Xiao, Liang and Zhao, Dawei and Nie, Yiming and Dai, Bin},
  journal={IEEE Transactions on Intelligent Vehicles},
  year={2023},
  publisher={IEEE}
}