Extract predicted keypoint locations from heatmaps. Output has shape
    (#rois, 4, #keypoints) with the 4 rows corresponding to (x, y, logit, prob)
    for each keypoint.

def heatmaps_to_keypoints(maps, rois):
    """Extract predicted keypoint locations from heatmaps. Output has shape
    (#rois, 4, #keypoints) with the 4 rows corresponding to (x, y, logit, prob)
    for each keypoint.
    """
    # This function converts a discrete image coordinate in a HEATMAP_SIZE x
    # HEATMAP_SIZE image to a continuous keypoint coordinate. We maintain
    # consistency with keypoints_to_heatmap_labels by using the conversion from
    # Heckbert 1990: c = d + 0.5, where d is a discrete coordinate and c is a
    # continuous coordinate.
    offset_x = rois[:, 0]
    offset_y = rois[:, 1]

    widths = rois[:, 2] - rois[:, 0]
    heights = rois[:, 3] - rois[:, 1]
    widths = np.maximum(widths, 1)
    heights = np.maximum(heights, 1)
    widths_ceil = np.ceil(widths)
    heights_ceil = np.ceil(heights)

    # NCHW to NHWC for use with OpenCV
    maps = np.transpose(maps, [0, 2, 3, 1])
    min_size = 0  # cfg.KRCNN.INFERENCE_MIN_SIZE
    num_keypoints = maps.shape[3]
    xy_preds = np.zeros((len(rois), 3, num_keypoints), dtype=np.float32)
    end_scores = np.zeros((len(rois), num_keypoints), dtype=np.float32)
    for i in range(len(rois)):
        if min_size > 0:
            roi_map_width = int(np.maximum(widths_ceil[i], min_size))
            roi_map_height = int(np.maximum(heights_ceil[i], min_size))
        else:
            roi_map_width = widths_ceil[i]
            roi_map_height = heights_ceil[i]
        width_correction = widths[i] / roi_map_width
        height_correction = heights[i] / roi_map_height
        roi_map = cv2.resize(
            maps[i], (roi_map_width, roi_map_height), interpolation=cv2.INTER_CUBIC
        )
        # Bring back to CHW
        roi_map = np.transpose(roi_map, [2, 0, 1])
        # roi_map_probs = scores_to_probs(roi_map.copy())
        w = roi_map.shape[2]
        pos = roi_map.reshape(num_keypoints, -1).argmax(axis=1)
        x_int = pos % w
        y_int = (pos - x_int) // w
        # assert (roi_map_probs[k, y_int, x_int] ==
        #         roi_map_probs[k, :, :].max())
        x = (x_int + 0.5) * width_correction
        y = (y_int + 0.5) * height_correction
        xy_preds[i, 0, :] = x + offset_x[i]
        xy_preds[i, 1, :] = y + offset_y[i]
        xy_preds[i, 2, :] = 1
        end_scores[i, :] = roi_map[np.arange(num_keypoints), y_int, x_int]

    return np.transpose(xy_preds, [0, 2, 1]), end_scores