#IOU come reward
    if action == 6 and self.end:
        if current_iou >= 0.5:
            reward += 100 * current_iou
            terminated = True
            step_info = f"SUCCESS IoU: {current_iou:.2f}"
        else:
            reward -= 20
            terminated = True
            step_info = f"FALSE_ALARM IoU: {current_iou:.2f}"
    elif action == 6:
        if current_iou >= 0.5:
            reward = 100 * current_iou      # IoU = 0.6 * 80→ reward = 48
            terminated = True
            step_info = f"SUCCESS IoU: {current_iou:.2f}"
        else:
            reward = -20                   # big penalty to avoid early trigger
            terminated = True
            step_info = f"FALSE_ALARM IoU: {current_iou:.2f}"
    else:
        delta_iou = current_iou - self.prev_iou

        # Encourage improvement
        reward = 30 * delta_iou            # if IoU increases +0.1 * 10→ reward = +1

        # If object not visible, use distance shaping
        if current_iou == 0:
            delta_dist = prev_dist - curr_dist
            reward += 10 * delta_dist    # avoid too large values