# Center-based 3D Object Detection and Tracking

## Abstract

<!-- [ABSTRACT] -->

Three-dimensional objects are commonly represented as 3D boxes in a point-cloud. This representation mimics the well-studied image-based 2D bounding-box detection but comes with additional challenges. Objects in a 3D world do not follow any particular orientation, and box-based detectors have difficulties enumerating all orientations or fitting an axis-aligned bounding box to rotated objects. In this paper, we instead propose to represent, detect, and track 3D objects as points. Our framework, CenterPoint, first detects centers of objects using a keypoint detector and regresses to other attributes, including 3D size, 3D orientation, and velocity. In a second stage, it refines these estimates using additional point features on the object. In CenterPoint, 3D object tracking simplifies to greedy closest-point matching. The resulting detection and tracking algorithm is simple, efficient, and effective. CenterPoint achieved state-of-the-art performance on the nuScenes benchmark for both 3D detection and tracking, with 65.5 NDS and 63.8 AMOTA for a single model. On the Waymo Open Dataset, CenterPoint outperforms all previous single model method by a large margin and ranks first among all Lidar-only submissions.

<!-- [IMAGE] -->

<div align=center>
<img src="https://user-images.githubusercontent.com/30491025/143854976-11af75ae-e828-43ad-835d-ac1146f99925.png" width="800"/>
</div>

<!-- [PAPER_TITLE: Center-based 3D Object Detection and Tracking] -->
<!-- [PAPER_URL: https://arxiv.org/abs/2006.11275] -->

## Introduction

<!-- [ALGORITHM] -->

We implement CenterPoint and provide the result and checkpoints on nuScenes dataset.

We follow the below style to name config files. Contributors are advised to follow the same style.
`{xxx}` is required field and `[yyy]` is optional.

`{model}`: model type like `centerpoint`.

`{model setting}`: voxel size and voxel type like `01voxel`, `02pillar`.

`{backbone}`: backbone type like `second`.

`{neck}`: neck type like `secfpn`.

`[dcn]`: Whether to use deformable convolution.

`[circle]`: Whether to use circular nms.

`[batch_per_gpu x gpu]`: GPUs and samples per GPU, 4x8 is used by default.

`{schedule}`: training schedule, options are 1x, 2x, 20e, etc. 1x and 2x means 12 epochs and 24 epochs respectively. 20e is adopted in cascade models, which denotes 20 epochs. For 1x/2x, initial learning rate decays by a factor of 10 at the 8/16th and 11/22th epochs. For 20e, initial learning rate decays by a factor of 10 at the 16th and 19th epochs.

`{dataset}`: dataset like nus-3d, kitti-3d, lyft-3d, scannet-3d, sunrgbd-3d. We also indicate the number of classes we are using if there exist multiple settings, e.g., kitti-3d-3class and kitti-3d-car means training on KITTI dataset with 3 classes and single class, respectively.

```
@article{yin2021center,
  title={Center-based 3D Object Detection and Tracking},
  author={Yin, Tianwei and Zhou, Xingyi and Kr{\"a}henb{\"u}hl, Philipp},
  journal={CVPR},
  year={2021},
}
```

## Usage

### Test time augmentation

We have supported double-flip and scale augmentation during test time. To use test time augmentation, users need to modify the
`test_pipeline` and `test_cfg` in the config.
For example, we change `centerpoint_0075voxel_second_secfpn_circlenms_4x8_cyclic_20e_nus.py` to the following.

```python
_base_ = './centerpoint_0075voxel_second_secfpn_circlenms' \
         '_4x8_cyclic_20e_nus.py'

model = dict(
    test_cfg=dict(
        pts=dict(
            use_rotate_nms=True,
            max_num=83)))

point_cloud_range = [-54, -54, -5.0, 54, 54, 3.0]
file_client_args = dict(backend='disk')
class_names = [
    'car', 'truck', 'construction_vehicle', 'bus', 'trailer', 'barrier',
    'motorcycle', 'bicycle', 'pedestrian', 'traffic_cone'
]

test_pipeline = [
    dict(
        type='LoadPointsFromFile',
        load_dim=5,
        use_dim=5,
        file_client_args=file_client_args),
    dict(
        type='LoadPointsFromMultiSweeps',
        sweeps_num=9,
        use_dim=[0, 1, 2, 3, 4],
        file_client_args=file_client_args,
        pad_empty_sweeps=True,
        remove_close=True),
    dict(
        type='MultiScaleFlipAug3D',
        img_scale=(1333, 800),
        pts_scale_ratio=[0.95, 1.0, 1.05],
        flip=True,
        pcd_horizontal_flip=True,
        pcd_vertical_flip=True,
        transforms=[
            dict(
                type='GlobalRotScaleTrans',
                rot_range=[0, 0],
                scale_ratio_range=[1., 1.],
                translation_std=[0, 0, 0]),
            dict(type='RandomFlip3D', sync_2d=False),
            dict(
                type='PointsRangeFilter', point_cloud_range=point_cloud_range),
            dict(
                type='DefaultFormatBundle3D',
                class_names=class_names,
                with_label=False),
            dict(type='Collect3D', keys=['points'])
        ])
]

data = dict(
    val=dict(pipeline=test_pipeline), test=dict(pipeline=test_pipeline))

```

## Results

### CenterPoint

|Backbone|  Voxel type (voxel size)   |Dcn|Circular nms| Mem (GB) | Inf time (fps) | mAP |NDS| Download |
| :---------: |:-----: |:-----: | :------: | :------------: | :----: |:----: | :------: |:------: |
|[SECFPN](./centerpoint_01voxel_second_secfpn_circlenms_4x8_cyclic_20e_nus.py)|voxel (0.1)|✗|✓|4.9| |56.19|64.43|[model](https://download.openmmlab.com/mmdetection3d/v0.1.0_models/centerpoint/centerpoint_01voxel_second_secfpn_circlenms_4x8_cyclic_20e_nus/centerpoint_01voxel_second_secfpn_circlenms_4x8_cyclic_20e_nus_20201001_135205-5db91e00.pth) &#124; [log](https://download.openmmlab.com/mmdetection3d/v0.1.0_models/centerpoint/centerpoint_01voxel_second_secfpn_circlenms_4x8_cyclic_20e_nus/centerpoint_01voxel_second_secfpn_circlenms_4x8_cyclic_20e_nus_20201001_135205.log.json)|
|above w/o circle nms|voxel (0.1)|✗|✗| | |56.56|64.46||
|[SECFPN](./centerpoint_01voxel_second_secfpn_dcn_circlenms_4x8_cyclic_20e_nus.py)|voxel (0.1)|✓|✓|5.2| |56.34|64.81|[model](https://download.openmmlab.com/mmdetection3d/v0.1.0_models/centerpoint/centerpoint_01voxel_second_secfpn_dcn_circlenms_4x8_cyclic_20e_nus/centerpoint_01voxel_second_secfpn_dcn_circlenms_4x8_cyclic_20e_nus_20201004_075317-26d8176c.pth) &#124; [log](https://download.openmmlab.com/mmdetection3d/v0.1.0_models/centerpoint/centerpoint_01voxel_second_secfpn_dcn_circlenms_4x8_cyclic_20e_nus/centerpoint_01voxel_second_secfpn_dcn_circlenms_4x8_cyclic_20e_nus_20201004_075317.log.json)|
|above w/o circle nms|voxel (0.1)|✓|✗| | |56.60|64.90||
|[SECFPN](./centerpoint_0075voxel_second_secfpn_circlenms_4x8_cyclic_20e_nus.py)|voxel (0.075)|✗|✓|7.8| |57.34|65.23|[model](https://download.openmmlab.com/mmdetection3d/v0.1.0_models/centerpoint/centerpoint_0075voxel_second_secfpn_circlenms_4x8_cyclic_20e_nus/centerpoint_0075voxel_second_secfpn_circlenms_4x8_cyclic_20e_nus_20200925_230905-358fbe3b.pth) &#124; [log](https://download.openmmlab.com/mmdetection3d/v0.1.0_models/centerpoint/centerpoint_0075voxel_second_secfpn_circlenms_4x8_cyclic_20e_nus/centerpoint_0075voxel_second_secfpn_circlenms_4x8_cyclic_20e_nus_20200925_230905.log.json)|
|above w/o circle nms|voxel (0.075)|✗|✗| | |57.63|65.39| |
|[SECFPN](./centerpoint_0075voxel_second_secfpn_dcn_circlenms_4x8_cyclic_20e_nus.py)|voxel (0.075)|✓|✓|8.5| |57.27|65.58|[model](https://download.openmmlab.com/mmdetection3d/v0.1.0_models/centerpoint/centerpoint_0075voxel_second_secfpn_dcn_circlenms_4x8_cyclic_20e_nus/centerpoint_0075voxel_second_secfpn_dcn_circlenms_4x8_cyclic_20e_nus_20200930_201619-67c8496f.pth) &#124; [log](https://download.openmmlab.com/mmdetection3d/v0.1.0_models/centerpoint/centerpoint_0075voxel_second_secfpn_dcn_circlenms_4x8_cyclic_20e_nus/centerpoint_0075voxel_second_secfpn_dcn_circlenms_4x8_cyclic_20e_nus_20200930_201619.log.json)|
|above w/o circle nms|voxel (0.075)|✓|✗| | |57.43|65.63||
|above w/ double flip|voxel (0.075)|✓|✗| | |59.73|67.39||
|above w/ scale tta|voxel (0.075)|✓|✗| | |60.43|67.65||
|above w/ circle nms w/o scale tta|voxel (0.075)|✓|✗| | |59.52|67.24||
|[SECFPN](./centerpoint_02pillar_second_secfpn_circlenms_4x8_cyclic_20e_nus.py)|pillar (0.2)|✗|✓|4.4| |49.07|59.66|[model](https://download.openmmlab.com/mmdetection3d/v0.1.0_models/centerpoint/centerpoint_02pillar_second_secfpn_circlenms_4x8_cyclic_20e_nus/centerpoint_02pillar_second_secfpn_circlenms_4x8_cyclic_20e_nus_20201004_170716-a134a233.pth) &#124; [log](https://download.openmmlab.com/mmdetection3d/v0.1.0_models/centerpoint/centerpoint_02pillar_second_secfpn_circlenms_4x8_cyclic_20e_nus/centerpoint_02pillar_second_secfpn_circlenms_4x8_cyclic_20e_nus_20201004_170716.log.json)|
|above w/o circle nms|pillar (0.2)|✗|✗| | |49.12|59.66||
|[SECFPN](./centerpoint_02pillar_second_secfpn_dcn_4x8_cyclic_20e_nus.py)|pillar (0.2)|✓|✗| 4.6| |48.8 |59.67 |[model](https://download.openmmlab.com/mmdetection3d/v0.1.0_models/centerpoint/centerpoint_02pillar_second_secfpn_dcn_4x8_cyclic_20e_nus/centerpoint_02pillar_second_secfpn_dcn_4x8_cyclic_20e_nus_20200930_103722-3bb135f2.pth) &#124; [log](https://download.openmmlab.com/mmdetection3d/v0.1.0_models/centerpoint/centerpoint_02pillar_second_secfpn_dcn_4x8_cyclic_20e_nus/centerpoint_02pillar_second_secfpn_dcn_4x8_cyclic_20e_nus_20200930_103722.log.json)|
|above w/ circle nms|pillar (0.2)|✓|✓| | |48.79|59.65||
