> For the complete documentation index, see [llms.txt](https://pcl.gitbook.io/tutorial/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://pcl.gitbook.io/tutorial/part-1/part01-chapter03/part01-chapter03-practice.md).

# ROS 실습 (90%)

[![Alt text](https://img.youtube.com/vi/wM7EYNyzejQ/0.jpg)](https://www.youtube.com/watch?v=wM7EYNyzejQ)

실습에서는 **PCL-Python 기반 관심영역 설정**에서 정의한 `do_passthrough()`를 사용하여 수신된 Raw데이터에서 관심영역 설정 하여 출력 해보도록 하겠습니다.

관심 영역은 중앙 로비 부분 이며 상하좌우는 모두 제거 하였습니다. 기본 구조는 이전챕터에서 살펴본 \[ROS 기반 I/O]와 동일 합니다.

```python
#!/usr/bin/env python3
# coding: utf-8

import rospy
from sensor_msgs.msg import PointCloud2
import sensor_msgs.point_cloud2 as pc2

import pcl
import pcl_helper

def do_passthrough(pcl_data,filter_axis,axis_min,axis_max):
    '''
    Create a PassThrough  object and assigns a filter axis and range.
    :param pcl_data: point could data subscriber
    :param filter_axis: filter axis
    :param axis_min: Minimum  axis to the passthrough filter object
    :param axis_max: Maximum axis to the passthrough filter object
    :return: passthrough on point cloud
    '''
    passthrough = pcl_data.make_passthrough_filter()
    passthrough.set_filter_field_name(filter_axis)
    passthrough.set_filter_limits(axis_min, axis_max)
    return passthrough.filter()

def callback(input_ros_msg):
    cloud = pcl_helper.ros_to_pcl(input_ros_msg)    

    # 실행 코드 부분 
    filter_axis = 'x'
    axis_min = 1.0
    axis_max = 20.0
    cloud = do_passthrough(cloud, filter_axis, axis_min, axis_max)

    filter_axis = 'y'
    axis_min = -7.0
    axis_max = 5.5
    cloud = do_passthrough(cloud, filter_axis, axis_min, axis_max)

    cloud_new = pcl_helper.pcl_to_ros(cloud) #PCL을 ROS 메시지로 변경     
    pub.publish(cloud_new)

if __name__ == "__main__":
    rospy.init_node('tutorial', anonymous=True)

    rospy.Subscriber('velodyne_points', PointCloud2, callback)
    pub = rospy.Publisher("/velodyne_points_new", PointCloud2, queue_size=1)

    rospy.spin()
```


---

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