Biography

I am pursuing my M.S. degree in College of Control Science and Engineering, Zhejiang University, Hangzhou, China. My major research interests include SLAM, 3DV and deep learning.

Research and Interests

• SLAM
• 3DV
• Deep learning

Publications

• Chencan Fu, Lin Li, Jianbiao Mei, Yukai Ma, Linpeng Peng, Xiangrui Zhao, and Yong Liu. A Coarse-to-Fine Place Recognition Approach using Attention-guided Descriptors and Overlap Estimation. In 2024 IEEE International Conference on Robotics and Automation (ICRA), pages 8493-8499, 2024.
  [BibTeX] [Abstract] [DOI] [PDF]

  Place recognition is a challenging but crucial task in robotics. Current description-based methods may be limited by representation capabilities, while pairwise similarity-based methods require exhaustive searches, which is time-consuming. In this paper, we present a novel coarse-to-fine approach to address these problems, which combines BEV (Bird’s Eye View) feature extraction, coarse-grained matching and fine-grained verification. In the coarse stage, our approach utilizes an attention-guided network to generate attention-guided descriptors. We then employ a fast affinity-based candidate selection process to identify the Top-K most similar candidates. In the fine stage, we estimate pairwise overlap among the narrowed-down place candidates to determine the final match. Experimental results on the KITTI and KITTI-360 datasets demonstrate that our approach outperforms state-of-the-art methods. The code will be released publicly soon.

  @inproceedings{fu2024ctf,
  title = {A Coarse-to-Fine Place Recognition Approach using Attention-guided Descriptors and Overlap Estimation},
  author = {Chencan Fu and Lin Li and Jianbiao Mei and Yukai Ma and Linpeng Peng and Xiangrui Zhao and Yong Liu},
  year = 2024,
  booktitle = {2024 IEEE International Conference on Robotics and Automation (ICRA)},
  pages = {8493-8499},
  doi = {10.1109/ICRA57147.2024.10611569},
  abstract = {Place recognition is a challenging but crucial task in robotics. Current description-based methods may be limited by representation capabilities, while pairwise similarity-based methods require exhaustive searches, which is time-consuming. In this paper, we present a novel coarse-to-fine approach to address these problems, which combines BEV (Bird's Eye View) feature extraction, coarse-grained matching and fine-grained verification. In the coarse stage, our approach utilizes an attention-guided network to generate attention-guided descriptors. We then employ a fast affinity-based candidate selection process to identify the Top-K most similar candidates. In the fine stage, we estimate pairwise overlap among the narrowed-down place candidates to determine the final match. Experimental results on the KITTI and KITTI-360 datasets demonstrate that our approach outperforms state-of-the-art methods. The code will be released publicly soon.}
  }

• Lina Liu, Xibin Song, Jiadai Sun, Xiaoyang Lyu, Lin Li, Yong Liu, and Liangjun Zhang. MFF-Net: Towards Efficient Monocular Depth Completion with Multi-Modal Feature Fusion. IEEE Robotics and Automation Letters (RA-L), 8:920-927, 2023.
  [BibTeX] [Abstract] [DOI] [PDF]

  Remarkable progress has been achieved by current depth completion approaches, which produce dense depth maps from sparse depth maps and corresponding color images. However, the performances of these approaches are limited due to the insufficient feature extractions and fusions. In this work, we propose an efficient multi-modal feature fusion based depth completion framework (MFF-Net), which can efficiently extract and fuse features with different modals in both encoding and decoding processes, thus more depth details with better performance can be obtained. In specific, the encoding process contains three branches where different modals of features from both color and sparse depth input can be extracted, and a multi-feature channel shuffle is utilized to enhance these features thus features with better representation abilities can be obtained. Meanwhile, the decoding process contains two branches to sufficiently fuse the extracted multi-modal features, and a multi-level weighted combination is employed to further enhance and fuse features with different modals, thus leading to more accurate and better refined depth maps. Extensive experiments on different benchmarks demonstrate that we achieve state-of-the-art among online methods. Meanwhile, we further evaluate the predicted dense depth by RGB-D SLAM, which is a commonly used downstream robotic perception task, and higher accuracy on vehicle’s trajectory can be obtained in KITTI odometry dataset, which demonstrates the high quality of our depth prediction and the potential of improving the related downstream tasks with depth completion results.

  @article{liu2023mff,
  title = {MFF-Net: Towards Efficient Monocular Depth Completion with Multi-Modal Feature Fusion},
  author = {Lina Liu and Xibin Song and Jiadai Sun and Xiaoyang Lyu and Lin Li and Yong Liu and Liangjun Zhang},
  year = 2023,
  journal = {IEEE Robotics and Automation Letters (RA-L)},
  volume = 8,
  pages = {920-927},
  doi = {10.1109/LRA.2023.3234776},
  abstract = {Remarkable progress has been achieved by current depth completion approaches, which produce dense depth maps from sparse depth maps and corresponding color images. However, the performances of these approaches are limited due to the insufficient feature extractions and fusions. In this work, we propose an efficient multi-modal feature fusion based depth completion framework (MFF-Net), which can efficiently extract and fuse features with different modals in both encoding and decoding processes, thus more depth details with better performance can be obtained. In specific, the encoding process contains three branches where different modals of features from both color and sparse depth input can be extracted, and a multi-feature channel shuffle is utilized to enhance these features thus features with better representation abilities can be obtained. Meanwhile, the decoding process contains two branches to sufficiently fuse the extracted multi-modal features, and a multi-level weighted combination is employed to further enhance and fuse features with different modals, thus leading to more accurate and better refined depth maps. Extensive experiments on different benchmarks demonstrate that we achieve state-of-the-art among online methods. Meanwhile, we further evaluate the predicted dense depth by RGB-D SLAM, which is a commonly used downstream robotic perception task, and higher accuracy on vehicle's trajectory can be obtained in KITTI odometry dataset, which demonstrates the high quality of our depth prediction and the potential of improving the related downstream tasks with depth completion results.}
  }

• Tianxin Huang, Hao Zou, Jinhao Cui, Jiangning Zhang, Xuemeng Yang, Lin Li, and Yong Liu. Adaptive Recurrent Forward Network for Dense Point Cloud Completion. IEEE Transactions on Multimedia, 25:5903-5915, 2023.
  [BibTeX] [Abstract] [DOI] [PDF]

  Point cloud completion is an interesting and challenging task in 3D vision, which aims to recover complete shapes from sparse and incomplete point clouds. Existing completion networks often require a vast number of parameters and substantial computational costs to achieve a high performance level, which may limit their practical application. In this work, we propose a novel Adaptive efficient Recurrent Forward Network (ARFNet), which is composed of three parts: Recurrent Feature Extraction (RFE), Forward Dense Completion (FDC) and Raw Shape Protection (RSP). In an RFE, multiple short global features are extracted from incomplete point clouds, while a dense quantity of completed results are generated in a coarse-to-fine pipeline in the FDC. Finally, we propose the Adamerge module to preserve the details from the original models by merging the generated results with the original incomplete point clouds in the RSP. In addition, we introduce the Sampling Chamfer Distance to better capture the shapes of the models and the balanced expansion constraint to restrict the expansion distances from coarse to fine. According to the experiments on ShapeNet and KITTI, our network can achieve state-of-the-art completion performances on dense point clouds with fewer parameters, smaller model sizes, lower memory costs and a faster convergence.

  @article{huang2022arf,
  title = {Adaptive Recurrent Forward Network for Dense Point Cloud Completion},
  author = {Tianxin Huang and Hao Zou and Jinhao Cui and Jiangning Zhang and Xuemeng Yang and Lin Li and Yong Liu},
  year = 2023,
  journal = {IEEE Transactions on Multimedia},
  volume = {25},
  pages = {5903-5915},
  doi = {10.1109/TMM.2022.3200851},
  abstract = {Point cloud completion is an interesting and challenging task in 3D vision, which aims to recover complete shapes from sparse and incomplete point clouds. Existing completion networks often require a vast number of parameters and substantial computational costs to achieve a high performance level, which may limit their practical application. In this work, we propose a novel Adaptive efficient Recurrent Forward Network (ARFNet), which is composed of three parts: Recurrent Feature Extraction (RFE), Forward Dense Completion (FDC) and Raw Shape Protection (RSP). In an RFE, multiple short global features are extracted from incomplete point clouds, while a dense quantity of completed results are generated in a coarse-to-fine pipeline in the FDC. Finally, we propose the Adamerge module to preserve the details from the original models by merging the generated results with the original incomplete point clouds in the RSP. In addition, we introduce the Sampling Chamfer Distance to better capture the shapes of the models and the balanced expansion constraint to restrict the expansion distances from coarse to fine. According to the experiments on ShapeNet and KITTI, our network can achieve state-of-the-art completion performances on dense point clouds with fewer parameters, smaller model sizes, lower memory costs and a faster convergence.}
  }

• Lin Li, Wendong Ding, Yongkun Wen, Yufei Liang, Yong Liu, and Guowei Wan. A Unified BEV Model for Joint Learning 3D Local Features and Overlap Estimation. In 2023 IEEE International Conference on Robotics and Automation (ICRA), pages 8341-8348, 2023.
  [BibTeX] [Abstract] [DOI] [PDF]

  Pairwise point cloud registration is a critical task for many applications, which heavily depends on finding correct correspondences from the two point clouds. However, the low overlap between input point clouds causes the registration to fail easily, leading to mistaken overlapping and mismatched correspondences, especially in scenes where non-overlapping regions contain similar structures. In this paper, we present a unified bird’s-eye view (BEV) model for jointly learning of 3D local features and overlap estimation to fulfill pairwise registration and loop closure. Feature description is performed by a sparse UNet-like network based on BEV representation, and 3D keypoints are extracted by a detection head for 2D locations, and a regression head for heights. For overlap detection, a cross-attention module is applied for interacting contextual information of input point clouds, followed by a classification head to estimate the overlapping region. We evaluate our unified model extensively on the KITTI dataset and Apollo-SouthBay dataset. The experiments demonstrate that our method significantly outperforms existing methods on overlap estimation, especially in scenes with small overlaps. It also achieves top registration performance on both datasets in terms of translation and rotation errors.

  @inproceedings{li2023bev,
  title = {A Unified BEV Model for Joint Learning 3D Local Features and Overlap Estimation},
  author = {Lin Li and Wendong Ding and Yongkun Wen and Yufei Liang and Yong Liu and Guowei Wan},
  year = 2023,
  booktitle = {2023 IEEE International Conference on Robotics and Automation (ICRA)},
  pages = {8341-8348},
  doi = {10.1109/ICRA48891.2023.10160492},
  abstract = {Pairwise point cloud registration is a critical task for many applications, which heavily depends on finding correct correspondences from the two point clouds. However, the low overlap between input point clouds causes the registration to fail easily, leading to mistaken overlapping and mismatched correspondences, especially in scenes where non-overlapping regions contain similar structures. In this paper, we present a unified bird's-eye view (BEV) model for jointly learning of 3D local features and overlap estimation to fulfill pairwise registration and loop closure. Feature description is performed by a sparse UNet-like network based on BEV representation, and 3D keypoints are extracted by a detection head for 2D locations, and a regression head for heights. For overlap detection, a cross-attention module is applied for interacting contextual information of input point clouds, followed by a classification head to estimate the overlapping region. We evaluate our unified model extensively on the KITTI dataset and Apollo-SouthBay dataset. The experiments demonstrate that our method significantly outperforms existing methods on overlap estimation, especially in scenes with small overlaps. It also achieves top registration performance on both datasets in terms of translation and rotation errors.}
  }

• Lin Li, Xin Kong, Xiangrui Zhao, Tianxin Huang, and Yong Liu. Semantic Scan Context: A Novel Semantic-based Loop-closure Method for LiDAR SLAM. Autonomous Robots, 46(4):535-551, 2022.
  [BibTeX] [Abstract] [DOI] [PDF]

  As one of the key technologies of SLAM, loop-closure detection can help eliminate the cumulative errors of the odometry. Many of the current LiDAR-based SLAM systems do not integrate a loop-closure detection module, so they will inevitably suffer from cumulative errors. This paper proposes a semantic-based place recognition method called Semantic Scan Context (SSC), which consists of the two-step global ICP and the semantic-based descriptor. Thanks to the use of high-level semantic features, our descriptor can effectively encode scene information. The proposed two-step global ICP can help eliminate the influence of rotation and translation on descriptor matching and provide a good initial value for geometric verification. Further, we built a complete loop-closure detection module based on SSC and combined it with the famous LOAM to form a full LiDAR SLAM system. Exhaustive experiments on the KITTI and KITTI-360 datasets show that our approach is competitive to the state-of-the-art methods, robust to the environment, and has good generalization ability. Our code is available at:https://github.com/lilin-hitcrt/SSC.

  @article{li2022ssc,
  title = {Semantic Scan Context: A Novel Semantic-based Loop-closure Method for LiDAR SLAM},
  author = {Lin Li and Xin Kong and Xiangrui Zhao and Tianxin Huang and Yong Liu},
  year = 2022,
  journal = {Autonomous Robots},
  volume = {46},
  number = {4},
  pages = {535-551},
  doi = {10.1007/s10514-022-10037-w},
  abstract = {As one of the key technologies of SLAM, loop-closure detection can help eliminate the cumulative errors of the odometry. Many of the current LiDAR-based SLAM systems do not integrate a loop-closure detection module, so they will inevitably suffer from cumulative errors. This paper proposes a semantic-based place recognition method called Semantic Scan Context (SSC), which consists of the two-step global ICP and the semantic-based descriptor. Thanks to the use of high-level semantic features, our descriptor can effectively encode scene information. The proposed two-step global ICP can help eliminate the influence of rotation and translation on descriptor matching and provide a good initial value for geometric verification. Further, we built a complete loop-closure detection module based on SSC and combined it with the famous LOAM to form a full LiDAR SLAM system. Exhaustive experiments on the KITTI and KITTI-360 datasets show that our approach is competitive to the state-of-the-art methods, robust to the environment, and has good generalization ability. Our code is available at:https://github.com/lilin-hitcrt/SSC.}
  }

• Lin Li, Xin Kong, Xiangrui Zhao, Tianxin Huang, Wanlong li, Feng Wen, Hongbo Zhang, and Yong Liu. RINet: Efficient 3D Lidar-Based Place Recognition Using Rotation Invariant Neural Network. IEEE Robotics and Automation Letters (RA-L), 7(2):4321-4328, 2022.
  [BibTeX] [Abstract] [DOI] [PDF]

  LiDAR-based place recognition (LPR) is one of the basic capabilities of robots, which can retrieve scenes from maps and identify previously visited locations based on 3D point clouds. As robots often pass the same place from different views, LPR methods are supposed to be robust to rotation, which is lacking in most current learning-based approaches. In this letter, we propose a rotation invariant neural network structure that can detect reverse loop closures even training data is all in the same direction. Specifically, we design a novel rotation equivariant global descriptor, which combines semantic and geometric features to improve description ability. Then a rotation invariant siamese neural network is implemented to predict the similarity of descriptor pairs. Our network is lightweight and can operate more than 8000 FPS on an i7-9700 CPU. Exhaustive evaluations and robustness tests on the KITTI, KITTI-360, and NCLT datasets show that our approach can work stably in various scenarios and achieve state-of-the-art performance.

  @article{li2022rinet,
  title = {RINet: Efficient 3D Lidar-Based Place Recognition Using Rotation Invariant Neural Network},
  author = {Lin Li and Xin Kong and Xiangrui Zhao and Tianxin Huang and Wanlong li and Feng Wen and Hongbo Zhang and Yong Liu},
  year = 2022,
  journal = {IEEE Robotics and Automation Letters (RA-L)},
  volume = {7},
  number = {2},
  pages = {4321-4328},
  doi = {10.1109/LRA.2022.3150499},
  abstract = {LiDAR-based place recognition (LPR) is one of the basic capabilities of robots, which can retrieve scenes from maps and identify previously visited locations based on 3D point clouds. As robots often pass the same place from different views, LPR methods are supposed to be robust to rotation, which is lacking in most current learning-based approaches. In this letter, we propose a rotation invariant neural network structure that can detect reverse loop closures even training data is all in the same direction. Specifically, we design a novel rotation equivariant global descriptor, which combines semantic and geometric features to improve description ability. Then a rotation invariant siamese neural network is implemented to predict the similarity of descriptor pairs. Our network is lightweight and can operate more than 8000 FPS on an i7-9700 CPU. Exhaustive evaluations and robustness tests on the KITTI, KITTI-360, and NCLT datasets show that our approach can work stably in various scenarios and achieve state-of-the-art performance.}
  }

• Lin Li, Xin Kong, Xiangrui Zhao, Tianxin Huang, and Yong Liu. SSC: Semantic Scan Context for Large-Scale Place Recognition. In 2021 IEEE/RSJ International Conference on Intelligent Robots and Systems, pages 2092-2099, 2021.
  [BibTeX] [Abstract] [DOI] [PDF]

  Place recognition gives a SLAM system the ability to correct cumulative errors. Unlike images that contain rich texture features, point clouds are almost pure geometric information which makes place recognition based on point clouds challenging. Existing works usually encode low-level features such as coordinate, normal, reflection intensity, etc., as local or global descriptors to represent scenes. Besides, they often ignore the translation between point clouds when matching descriptors. Different from most existing methods, we explore the use of high-level features, namely semantics, to improve the descriptor’s representation ability. Also, when matching descriptors, we try to correct the translation between point clouds to improve accuracy. Concretely, we propose a novel global descriptor, Semantic Scan Context, which explores semantic information to represent scenes more effectively. We also present a two-step global semantic ICP to obtain the 3D pose (x, y, yaw) used to align the point cloud to improve matching performance. Our experiments on the KITTI dataset show that our approach outperforms the state-of-the-art methods with a large margin. Our code is available at: https://github.com/lilin-hitcrt/SSC.

  @inproceedings{li2021ssc,
  title = {SSC: Semantic Scan Context for Large-Scale Place Recognition},
  author = {Lin Li and Xin Kong and Xiangrui Zhao and Tianxin Huang and Yong Liu},
  year = 2021,
  booktitle = {2021 IEEE/RSJ International Conference on Intelligent Robots and Systems},
  pages = {2092-2099},
  doi = {https://doi.org/10.1109/IROS51168.2021.9635904},
  abstract = {Place recognition gives a SLAM system the ability to correct cumulative errors. Unlike images that contain rich texture features, point clouds are almost pure geometric information which makes place recognition based on point clouds challenging. Existing works usually encode low-level features such as coordinate, normal, reflection intensity, etc., as local or global descriptors to represent scenes. Besides, they often ignore the translation between point clouds when matching descriptors. Different from most existing methods, we explore the use of high-level features, namely semantics, to improve the descriptor’s representation ability. Also, when matching descriptors, we try to correct the translation between point clouds to improve accuracy. Concretely, we propose a novel global descriptor, Semantic Scan Context, which explores semantic information to represent scenes more effectively. We also present a two-step global semantic ICP to obtain the 3D pose (x, y, yaw) used to align the point cloud to improve matching performance. Our experiments on the KITTI dataset show that our approach outperforms the state-of-the-art methods with a large margin. Our code is available at: https://github.com/lilin-hitcrt/SSC.}
  }

• Lin Li, Xin Kong, Xiangrui Zhao, and Yong Liu. SA-LOAM: Semantic-aided LiDAR SLAM with Loop Closure. In 2021 IEEE International Conference on Robotics and Automation, pages 7627-7634, 2021.
  [BibTeX] [Abstract] [DOI] [PDF]

  LiDAR-based SLAM system is admittedly more accurate and stable than others, while its loop closure de-tection is still an open issue. With the development of 3D semantic segmentation for point cloud, semantic information can be obtained conveniently and steadily, essential for high-level intelligence and conductive to SLAM. In this paper, we present a novel semantic-aided LiDAR SLAM with loop closure based on LOAM, named SA-LOAM, which leverages semantics in odometry as well as loop closure detection. Specifically, we propose a semantic-assisted ICP, including semantically matching, downsampling and plane constraint, and integrates a semantic graph-based place recognition method in our loop closure detection module. Benefitting from semantics, we can improve the localization accuracy, detect loop closures effec-tively, and construct a global consistent semantic map even in large-scale scenes. Extensive experiments on KITTI and Ford Campus dataset show that our system significantly improves baseline performance, has generalization ability to unseen data and achieves competitive results compared with state-of-the-art methods.

  @inproceedings{li2021ssa,
  title = {SA-LOAM: Semantic-aided LiDAR SLAM with Loop Closure},
  author = {Lin Li and Xin Kong and Xiangrui Zhao and Yong Liu},
  year = 2021,
  booktitle = {2021 IEEE International Conference on Robotics and Automation},
  pages = {7627-7634},
  doi = {https://doi.org/10.1109/ICRA48506.2021.9560884},
  abstract = {LiDAR-based SLAM system is admittedly more accurate and stable than others, while its loop closure de-tection is still an open issue. With the development of 3D semantic segmentation for point cloud, semantic information can be obtained conveniently and steadily, essential for high-level intelligence and conductive to SLAM. In this paper, we present a novel semantic-aided LiDAR SLAM with loop closure based on LOAM, named SA-LOAM, which leverages semantics in odometry as well as loop closure detection. Specifically, we propose a semantic-assisted ICP, including semantically matching, downsampling and plane constraint, and integrates a semantic graph-based place recognition method in our loop closure detection module. Benefitting from semantics, we can improve the localization accuracy, detect loop closures effec-tively, and construct a global consistent semantic map even in large-scale scenes. Extensive experiments on KITTI and Ford Campus dataset show that our system significantly improves baseline performance, has generalization ability to unseen data and achieves competitive results compared with state-of-the-art methods.}
  }