AI CityChallenge 2021 - Track 5

Public code for "All You Can Embed: Natural Language based Vehicle Retrieval with Spatio-Temporal Transformers", accepted as CVPR 2021 Workshop.
This work is our entry for the 5th AI City Challenge, Track 5: Natural-Language based Vehicle Retrieval.

[paper] [slides] [poster] [arXiv]

Model

Prerequisites

Environment

• Create a conda environment using the provided docs/environment.yml as described HERE
• To create an identical environment use docs/spec-file.txt

  conda create --name myenv --file spec-file.txt
  

Dataset

• Download AIC_2021 track 5 dataset and extract it somewhere
• Run extract_vdo_frms.py from <challenge_ds_root>/data to extract the individual frames from each video sequence (warning: you need to run the script for each S0x sequence, passed as argument).

Pre-process vehicle crops

To make the training faster the regions of the frames delimited by the tracking bounding boxes are extracted and saved.

$ cd data
$ python precompute_ego_crops.py --ds_root=<challenge_ds_root> --mode=train
$ python precompute_ego_crops.py --ds_root=<challenge_ds_root> --mode=test

Additionally, a --workers parameter can be set to parallelize the execution.

Precomputed Object-Embeddings

Object-Embeddings are part of the input to the model.

$ cd data
$ python precompute_rcnn_embs.py --ds_root=<challenge_ds_root> --mode=train
$ python precompute_rcnn_embs.py --ds_root=<challenge_ds_root> --mode=test

An additional --multi_process flag can be set to True to parallelize the execution across multiple GPUs, with a process per GPU.

Alternatively the pre-computed embeddings can be downloaded from HERE as rcnn_embs_t.tar.xz Extract the provided archive in <challenge_ds_root>.

Precomputed Language embeddings

Since the Visual Language are trained in separate stages the output of the latter is computed offline and used during the remainder of the training.

WARNING: This operation can be performed only after the training of the Language branch, alternatively you can download the pre-trained weights for the language branch, or the pre-computed Language embeddings.

$ cd data
$ python precompute_nl_embeddings.py --ds_root=<challenge_ds_root> --mode=train
$ python precompute_nl_embeddings.py --ds_root=<challenge_ds_root> --mode=test

The pre-computed embeddings can be downloaded from HERE as precomp_nl_t.tar.xz Extract the provided archive in <challenge_ds_root>.

Training

Language Branch

The training of the language branch is provided as a separate training script built with Pytorch Lightning. To reproduce the Language-Triple (LT) version used for the experiments presented on the paper:

  $ cd nlp
  $ python Bert_ft.py --ds_root=<challenge_ds_root>

This training is very phase and will take approximately 10 minutes on a single Nvidia RTX 2080Ti. When the training is finished a folder named bert_ft_experimental will ba saved into the nlp directory.

Pretrained: To instead use the pretrained weights download HERE the archive bert_finetuned.tar.xz and extract it to the nlp directory. Now you can execute the Precomputed Language embeddings procedure above.

Visual Branch

The best performing model (MRR=0.1078) has been trained on two Nvidia A100 GPUs, other hardware configurations have not been tested.

Edit the configuration file ./conf/experiments/best.yaml, the DATASET option must correspond to the absolute path to the extracted dataset, where you must also have the precomputed data.
Additionally the LOG_DIR option can be set to where you want to save training logs and checkpoints.

Run the training as follow:

  $ python main.py --exp_name=best! --seed=6969

WARNING: If you train on a different GPUs configuration please notice that the BATCH_SIZE option define the batch size for each of the available GPUs!

Inference

This operation will provide you with a .json result file in the format required for submission.

Run the training as follow:

  $ python main.py --exp_name=best --seed=6969 --mode=test

The output is saved to <LOG_DIR>/AYCE_2021/best/test_result.json

Pretrained weights

The pretrained weights for the best model are available for Download. Extract the provided archive best.zip and copy the trainin.ck file to <LOG_DIR>/AYCE_2021/best/, then perform the evaluation procedure.

Reference

@InProceedings{Scribano_2021_CVPR,
    author    = {Scribano, Carmelo and Sapienza, Davide and Franchini, Giorgia and Verucchi, Micaela and Bertogna, Marko},
    title     = {All You Can Embed: Natural Language Based Vehicle Retrieval With Spatio-Temporal Transformers},
    booktitle = {Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR) Workshops},
    month     = {June},
    year      = {2021},
    pages     = {4253-4262}
}