mmdet/models/task_modules/assigners/point_assigner.py

# Copyright (c) OpenMMLab. All rights reserved.
from typing import Optional

import torch
from mmengine.structures import InstanceData

from mmdet.registry import TASK_UTILS
from .assign_result import AssignResult
from .base_assigner import BaseAssigner


@TASK_UTILS.register_module()
class PointAssigner(BaseAssigner):
    """Assign a corresponding gt bbox or background to each point.

    Each proposals will be assigned with `0`, or a positive integer
    indicating the ground truth index.

    - 0: negative sample, no assigned gt
    - positive integer: positive sample, index (1-based) of assigned gt
    """

    def __init__(self, scale: int = 4, pos_num: int = 3) -> None:
        self.scale = scale
        self.pos_num = pos_num

    def assign(self,
               pred_instances: InstanceData,
               gt_instances: InstanceData,
               gt_instances_ignore: Optional[InstanceData] = None,
               **kwargs) -> AssignResult:
        """Assign gt to points.

        This method assign a gt bbox to every points set, each points set
        will be assigned with  the background_label (-1), or a label number.
        -1 is background, and semi-positive number is the index (0-based) of
        assigned gt.
        The assignment is done in following steps, the order matters.

        1. assign every points to the background_label (-1)
        2. A point is assigned to some gt bbox if
            (i) the point is within the k closest points to the gt bbox
            (ii) the distance between this point and the gt is smaller than
                other gt bboxes

        Args:
            pred_instances (:obj:`InstanceData`): Instances of model
                predictions. It includes ``priors``, and the priors can
                be anchors or points, or the bboxes predicted by the
                previous stage, has shape (n, 4). The bboxes predicted by
                the current model or stage will be named ``bboxes``,
                ``labels``, and ``scores``, the same as the ``InstanceData``
                in other places.


            gt_instances (:obj:`InstanceData`): Ground truth of instance
                annotations. It usually includes ``bboxes``, with shape (k, 4),
                and ``labels``, with shape (k, ).
            gt_instances_ignore (:obj:`InstanceData`, optional): Instances
                to be ignored during training. It includes ``bboxes``
                attribute data that is ignored during training and testing.
                Defaults to None.
        Returns:
            :obj:`AssignResult`: The assign result.
        """
        gt_bboxes = gt_instances.bboxes
        gt_labels = gt_instances.labels
        # points to be assigned, shape(n, 3) while last
        # dimension stands for (x, y, stride).
        points = pred_instances.priors

        num_points = points.shape[0]
        num_gts = gt_bboxes.shape[0]

        if num_gts == 0 or num_points == 0:
            # If no truth assign everything to the background
            assigned_gt_inds = points.new_full((num_points, ),
                                               0,
                                               dtype=torch.long)
            assigned_labels = points.new_full((num_points, ),
                                              -1,
                                              dtype=torch.long)
            return AssignResult(
                num_gts=num_gts,
                gt_inds=assigned_gt_inds,
                max_overlaps=None,
                labels=assigned_labels)

        points_xy = points[:, :2]
        points_stride = points[:, 2]
        points_lvl = torch.log2(
            points_stride).int()  # [3...,4...,5...,6...,7...]
        lvl_min, lvl_max = points_lvl.min(), points_lvl.max()

        # assign gt box
        gt_bboxes_xy = (gt_bboxes[:, :2] + gt_bboxes[:, 2:]) / 2
        gt_bboxes_wh = (gt_bboxes[:, 2:] - gt_bboxes[:, :2]).clamp(min=1e-6)
        scale = self.scale
        gt_bboxes_lvl = ((torch.log2(gt_bboxes_wh[:, 0] / scale) +
                          torch.log2(gt_bboxes_wh[:, 1] / scale)) / 2).int()
        gt_bboxes_lvl = torch.clamp(gt_bboxes_lvl, min=lvl_min, max=lvl_max)

        # stores the assigned gt index of each point
        assigned_gt_inds = points.new_zeros((num_points, ), dtype=torch.long)
        # stores the assigned gt dist (to this point) of each point
        assigned_gt_dist = points.new_full((num_points, ), float('inf'))
        points_range = torch.arange(points.shape[0])

        for idx in range(num_gts):
            gt_lvl = gt_bboxes_lvl[idx]
            # get the index of points in this level
            lvl_idx = gt_lvl == points_lvl
            points_index = points_range[lvl_idx]
            # get the points in this level
            lvl_points = points_xy[lvl_idx, :]
            # get the center point of gt
            gt_point = gt_bboxes_xy[[idx], :]
            # get width and height of gt
            gt_wh = gt_bboxes_wh[[idx], :]
            # compute the distance between gt center and
            #   all points in this level
            points_gt_dist = ((lvl_points - gt_point) / gt_wh).norm(dim=1)
            # find the nearest k points to gt center in this level
            min_dist, min_dist_index = torch.topk(
                points_gt_dist, self.pos_num, largest=False)
            # the index of nearest k points to gt center in this level
            min_dist_points_index = points_index[min_dist_index]
            # The less_than_recorded_index stores the index
            #   of min_dist that is less then the assigned_gt_dist. Where
            #   assigned_gt_dist stores the dist from previous assigned gt
            #   (if exist) to each point.
            less_than_recorded_index = min_dist < assigned_gt_dist[
                min_dist_points_index]
            # The min_dist_points_index stores the index of points satisfy:
            #   (1) it is k nearest to current gt center in this level.
            #   (2) it is closer to current gt center than other gt center.
            min_dist_points_index = min_dist_points_index[
                less_than_recorded_index]
            # assign the result
            assigned_gt_inds[min_dist_points_index] = idx + 1
            assigned_gt_dist[min_dist_points_index] = min_dist[
                less_than_recorded_index]

        assigned_labels = assigned_gt_inds.new_full((num_points, ), -1)
        pos_inds = torch.nonzero(
            assigned_gt_inds > 0, as_tuple=False).squeeze()
        if pos_inds.numel() > 0:
            assigned_labels[pos_inds] = gt_labels[assigned_gt_inds[pos_inds] -
                                                  1]

        return AssignResult(
            num_gts=num_gts,
            gt_inds=assigned_gt_inds,
            max_overlaps=None,
            labels=assigned_labels)