Source code for mmrotate.core.bbox.samplers.rotate_random_sampler

# Copyright (c) OpenMMLab. All rights reserved.
import torch
from mmdet.core.bbox.samplers.base_sampler import BaseSampler
from mmdet.core.bbox.samplers.sampling_result import SamplingResult

from ..builder import ROTATED_BBOX_SAMPLERS


@ROTATED_BBOX_SAMPLERS.register_module()
class RRandomSampler(BaseSampler):
    """Random sampler.

    Args:
        num (int): Number of samples
        pos_fraction (float): Fraction of positive samples
        neg_pos_up (int, optional): Upper bound number of negative and
            positive samples. Defaults to -1.
        add_gt_as_proposals (bool, optional): Whether to add ground truth
            boxes as proposals. Defaults to True.
    """

    def __init__(self,
                 num,
                 pos_fraction,
                 neg_pos_ub=-1,
                 add_gt_as_proposals=True,
                 **kwargs):
        from mmdet.core.bbox import demodata
        super(RRandomSampler, self).__init__(num, pos_fraction, neg_pos_ub,
                                             add_gt_as_proposals)
        self.rng = demodata.ensure_rng(kwargs.get('rng', None))

    def random_choice(self, gallery, num):
        """Random select some elements from the gallery.

        If `gallery` is a Tensor, the returned indices will be a Tensor;
        If `gallery` is a ndarray or list, the returned indices will be a
        ndarray.

        Args:
            gallery (Tensor | ndarray | list): indices pool.
            num (int): expected sample num.

        Returns:
            Tensor or ndarray: sampled indices.
        """
        assert len(gallery) >= num

        is_tensor = isinstance(gallery, torch.Tensor)
        if not is_tensor:
            gallery = torch.tensor(
                gallery, dtype=torch.long, device=torch.cuda.current_device())
        perm = torch.randperm(gallery.numel(), device=gallery.device)[:num]
        rand_inds = gallery[perm]
        if not is_tensor:
            rand_inds = rand_inds.cpu().numpy()
        return rand_inds

    def _sample_pos(self, assign_result, num_expected, **kwargs):
        """Randomly sample some positive samples."""
        pos_inds = torch.nonzero(assign_result.gt_inds > 0, as_tuple=False)
        if pos_inds.numel() != 0:
            pos_inds = pos_inds.squeeze(1)
        if pos_inds.numel() <= num_expected:
            return pos_inds
        else:
            return self.random_choice(pos_inds, num_expected)

    def _sample_neg(self, assign_result, num_expected, **kwargs):
        """Randomly sample some negative samples."""
        neg_inds = torch.nonzero(assign_result.gt_inds == 0, as_tuple=False)
        if neg_inds.numel() != 0:
            neg_inds = neg_inds.squeeze(1)
        if len(neg_inds) <= num_expected:
            return neg_inds
        else:
            return self.random_choice(neg_inds, num_expected)

    def sample(self,
               assign_result,
               bboxes,
               gt_bboxes,
               gt_labels=None,
               **kwargs):
        """Sample positive and negative bboxes.

        This is a simple implementation of bbox sampling given candidates,
        assigning results and ground truth bboxes.

        Args:
            assign_result (:obj:`AssignResult`): Bbox assigning results.
            bboxes (torch.Tensor): Boxes to be sampled from.
            gt_bboxes (torch.Tensor): Ground truth bboxes.
            gt_labels (Tensor, optional): Class labels of ground truth bboxes.

        Returns:
            :obj:`SamplingResult`: Sampling result.

        Example:
            >>> from mmdet.core.bbox import RandomSampler
            >>> from mmdet.core.bbox import AssignResult
            >>> from mmdet.core.bbox.demodata import ensure_rng, random_boxes
            >>> rng = ensure_rng(None)
            >>> assign_result = AssignResult.random(rng=rng)
            >>> bboxes = random_boxes(assign_result.num_preds, rng=rng)
            >>> gt_bboxes = random_boxes(assign_result.num_gts, rng=rng)
            >>> gt_labels = None
            >>> self = RandomSampler(num=32, pos_fraction=0.5, neg_pos_ub=-1,
            >>>                      add_gt_as_proposals=False)
            >>> self = self.sample(assign_result, bboxes, gt_bboxes, gt_labels)
        """
        if len(bboxes.shape) < 2:
            bboxes = bboxes[None, :]

        bboxes = bboxes[:, :5]

        gt_flags = bboxes.new_zeros((bboxes.shape[0], ), dtype=torch.uint8)
        if self.add_gt_as_proposals and len(gt_bboxes) > 0:
            if gt_labels is None:
                raise ValueError(
                    'gt_labels must be given when add_gt_as_proposals is True')
            bboxes = torch.cat([gt_bboxes, bboxes], dim=0)
            assign_result.add_gt_(gt_labels)
            gt_ones = bboxes.new_ones(gt_bboxes.shape[0], dtype=torch.uint8)
            gt_flags = torch.cat([gt_ones, gt_flags])

        num_expected_pos = int(self.num * self.pos_fraction)
        pos_inds = self.pos_sampler._sample_pos(
            assign_result, num_expected_pos, bboxes=bboxes, **kwargs)
        # We found that sampled indices have duplicated items occasionally.
        # (may be a bug of PyTorch)
        pos_inds = pos_inds.unique()
        num_sampled_pos = pos_inds.numel()
        num_expected_neg = self.num - num_sampled_pos
        if self.neg_pos_ub >= 0:
            _pos = max(1, num_sampled_pos)
            neg_upper_bound = int(self.neg_pos_ub * _pos)
            if num_expected_neg > neg_upper_bound:
                num_expected_neg = neg_upper_bound
        neg_inds = self.neg_sampler._sample_neg(
            assign_result, num_expected_neg, bboxes=bboxes, **kwargs)
        neg_inds = neg_inds.unique()

        sampling_result = SamplingResult(pos_inds, neg_inds, bboxes, gt_bboxes,
                                         assign_result, gt_flags)
        return sampling_result