def load_lvis_json(json_file, image_root, dataset_name=None, extra_annotation_keys=None):
    """
    Load a json file in LVIS's annotation format.

    Args:
        json_file (str): full path to the LVIS json annotation file.
        image_root (str): the directory where the images in this json file exists.
        dataset_name (str): the name of the dataset (e.g., "lvis_v0.5_train").
            If provided, this function will put "thing_classes" into the metadata
            associated with this dataset.
        extra_annotation_keys (list[str]): list of per-annotation keys that should also be
            loaded into the dataset dict (besides "bbox", "bbox_mode", "category_id",
            "segmentation"). The values for these keys will be returned as-is.

    Returns:
        list[dict]: a list of dicts in Detectron2 standard format. (See
        `Using Custom Datasets </tutorials/datasets.html>`_ )

    Notes:
        1. This function does not read the image files.
           The results do not have the "image" field.
    """
    from lvis import LVIS

    json_file = PathManager.get_local_path(json_file)

    timer = Timer()
    lvis_api = LVIS(json_file)
    if timer.seconds() > 1:
        logger.info("Loading {} takes {:.2f} seconds.".format(json_file, timer.seconds()))

    if dataset_name is not None:
        meta = get_lvis_instances_meta(dataset_name)
        MetadataCatalog.get(dataset_name).set(**meta)

    # sort indices for reproducible results
    img_ids = sorted(lvis_api.imgs.keys())
    # imgs is a list of dicts, each looks something like:
    # {'license': 4,
    #  'url': 'http://farm6.staticflickr.com/5454/9413846304_881d5e5c3b_z.jpg',
    #  'file_name': 'COCO_val2014_000000001268.jpg',
    #  'height': 427,
    #  'width': 640,
    #  'date_captured': '2013-11-17 05:57:24',
    #  'id': 1268}
    imgs = lvis_api.load_imgs(img_ids)
    # anns is a list[list[dict]], where each dict is an annotation
    # record for an object. The inner list enumerates the objects in an image
    # and the outer list enumerates over images. Example of anns[0]:
    # [{'segmentation': [[192.81,
    #     247.09,
    #     ...
    #     219.03,
    #     249.06]],
    #   'area': 1035.749,
    #   'image_id': 1268,
    #   'bbox': [192.81, 224.8, 74.73, 33.43],
    #   'category_id': 16,
    #   'id': 42986},
    #  ...]
    anns = [lvis_api.img_ann_map[img_id] for img_id in img_ids]

    # Sanity check that each annotation has a unique id
    ann_ids = [ann["id"] for anns_per_image in anns for ann in anns_per_image]
    assert len(set(ann_ids)) == len(ann_ids), "Annotation ids in '{}' are not unique".format(
        json_file
    )

    imgs_anns = list(zip(imgs, anns))

    logger.info("Loaded {} images in the LVIS format from {}".format(len(imgs_anns), json_file))

    if extra_annotation_keys:
        logger.info(
            "The following extra annotation keys will be loaded: {} ".format(extra_annotation_keys)
        )
    else:
        extra_annotation_keys = []

    def get_file_name(img_root, img_dict):
        # Determine the path including the split folder ("train2017", "val2017", "test2017") from
        # the coco_url field. Example:
        #   'coco_url': 'http://images.cocodataset.org/train2017/000000155379.jpg'
        split_folder, file_name = img_dict["coco_url"].split("/")[-2:]
        return os.path.join(img_root + split_folder, file_name)

    dataset_dicts = []

    for (img_dict, anno_dict_list) in imgs_anns:
        record = {}
        record["file_name"] = get_file_name(image_root, img_dict)
        record["height"] = img_dict["height"]
        record["width"] = img_dict["width"]
        record["not_exhaustive_category_ids"] = img_dict.get("not_exhaustive_category_ids", [])
        record["neg_category_ids"] = img_dict.get("neg_category_ids", [])
        image_id = record["image_id"] = img_dict["id"]

        objs = []
        for anno in anno_dict_list:
            # Check that the image_id in this annotation is the same as
            # the image_id we're looking at.
            # This fails only when the data parsing logic or the annotation file is buggy.
            assert anno["image_id"] == image_id
            obj = {"bbox": anno["bbox"], "bbox_mode": BoxMode.XYWH_ABS}
            # LVIS data loader can be used to load COCO dataset categories. In this case `meta`
            # variable will have a field with COCO-specific category mapping.
            if dataset_name is not None and "thing_dataset_id_to_contiguous_id" in meta:
                obj["category_id"] = meta["thing_dataset_id_to_contiguous_id"][anno["category_id"]]
            else:
                obj["category_id"] = anno["category_id"] - 1  # Convert 1-indexed to 0-indexed
            segm = anno["segmentation"]  # list[list[float]]
            # filter out invalid polygons (< 3 points)
            valid_segm = [poly for poly in segm if len(poly) % 2 == 0 and len(poly) >= 6]
            assert len(segm) == len(
                valid_segm
            ), "Annotation contains an invalid polygon with < 3 points"
            assert len(segm) > 0
            obj["segmentation"] = segm
            for extra_ann_key in extra_annotation_keys:
                obj[extra_ann_key] = anno[extra_ann_key]
            objs.append(obj)
        record["annotations"] = objs
        dataset_dicts.append(record)

    return dataset_dicts

    Load a json file in LVIS's annotation format.

    Args:
        json_file (str): full path to the LVIS json annotation file.
        image_root (str): the directory where the images in this json file exists.
        dataset_name (str): the name of the dataset (e.g., "lvis_v0.5_train").
            If provided, this function will put "thing_classes" into the metadata
            associated with this dataset.
        extra_annotation_keys (list[str]): list of per-annotation keys that should also be
            loaded into the dataset dict (besides "bbox", "bbox_mode", "category_id",
            "segmentation"). The values for these keys will be returned as-is.

    Returns:
        list[dict]: a list of dicts in Detectron2 standard format. (See
        `Using Custom Datasets </tutorials/datasets.html>`_ )

    Notes:
        1. This function does not read the image files.
           The results do not have the "image" field.
    
EVA-02/det/detectron2/data/datasets/lvis.py