This dataset is curated for the Natural Language (NL) Based Vehicle Retrieval Challenge Track of the 2021 AI City Workshop.

The workshop summary paper is available on ArXiv: https://arxiv.org/abs/2104.12233

@inproceedings{naphade2021AIC21,
author = {Milind Naphade and Shuo Wang and David C. Anastasiu and Zheng Tang and Ming-Ching Chang and Xiaodong Yang and Yue Yao and Liang Zheng
and Pranamesh Chakraborty and Anuj Sharma and Qi Feng and Vitaly Ablavsky and Stan Sclaroff},
title = {The 5th AI City Challenge},
booktitle = {The IEEE Conference on Computer Vision and Pattern Recognition (CVPR) Workshops},
month = {June},
year = {2021},
}

data/extract_vdo_frms.py is a Python script that is used to extract frames from videos provided in Challenge Track 3 (MTMC). Please use this script to extract frames, so that the path configurations in JSON files are consistent.

data/train-tracks.json is a dictionary of all 2,498 vehicle tracks in the training split. Each vehicle track is annotated with three natural language descriptions of the target and is assigned a universally unique identifier (UUID). The file is structured as

{
  "track-uuid-1": {
    "frames": ["file-1.jpg", ..., "file-n.jpg"],
    "boxes": [[742, 313, 171, 129], ..., [709, 304, 168, 125]],
    "nl": [
      "A gray pick-up truck goes ...", 
      "A dark pick-up runs ...", 
      "Pick-up truck that goes ..."
    ]
  },
  "track-uuid-2": ...
}

The files under the frames attribute are paths in the CityFlow Benchmark [2] used in Challenge Track 2 of the 2021 AI City Challenge.

data/test-tracks.json contains 530 tracks of target vehicles. The structure of this file is identical to the training split, except that the natural language descriptions are removed.

data/test-queries.json contains 530 queries. Each consists of three natural language descriptions of the vehicle target annotated by different annotators. Each query is assigned a UUID that is later used in results submission. The structure of this file is as follows:

{
  "query-uuid-1": [
    "A dark red SUV drives straight through an intersection.",
    "A red MPV crosses an empty intersection.",
    "A red SUV going straight down the street."
  ],
  "query-uuid-2": ...
}

The baseline/ directory contains a baseline model that measures the similarity between language descriptions and frame crops in a track. Details of this model can be found in [1].

Teams should retrieve and rank the provided vehicle tracks for each of the queries. A baseline retrieval model is provided as a demo for a start point for participating teams.

For each query, teams should submit a list of the testing tracks ranked by their retrieval model. One JSON file should be submitted containing a dictionary in the following format:

{
  "query-uuid-1": ["track-uuid-i", ..., "track-uuid-j"],
  "query-uuid-2": ["track-uuid-m", ..., "track-uuid-n"],
  ...
}

A sample JSON file of submission for the baseline model is available in baseline/baseline-results.json.

The Vehicle Retrieval by NL Descriptions task is evaluated using standard metrics for retrieval tasks. We use the Mean Reciprocal Rank (MRR) [3] as the main evaluation metric. Recall @ 5, Recall @ 10, and Recall @ 25 are also evaluated for all submissions.

The provided baseline model’s MRR is 0.0269, Recall @ 5 is 0.0264, Recall @ 10 is 0.0491, Recall @ 25 is 0.1113.

Please cite this work:

[1] Feng, Qi, et al. "CityFlow-NL: Tracking and Retrieval of Vehicles at City Scale by Natural Language Descriptions." arXiv preprint. arXiv:2101.04741.

[2] Tang, Zheng, et al. "CityFlow: A city-scale benchmark for multi-target multi-camera vehicle tracking and re-identification." CVPR. 2019.

[3] Voorhees, Ellen M. "The TREC-8 question answering track report." Trec. Vol. 99. 1999.