【ROS学习】ROS param 的使用

文章目录

• • 一、rosparam 命令行操作
  • 二、launch 文件载入param
  • 三、c++ 中操作 param
  • 四、python 中操作 param
  • 五、操作 param 时注意命名空间

参数服务器 Parammeter Server
参数服务器维护的是一个字典，里面存储的是key、value，每一个key对应一个value。

一、rosparam 命令行操作

1. 列出当前的所有参数：

rosparam list

2. 显示某个参数的值

rosparam get param_key

3. 设置某个参数的值

rosparam set param_key param_value

4. 保存参数到文件

rosparam dump file_name

5. 从文件读取参数

rosparam load file_name

注意这里的文件必须是YAML格式：YAML格式举例：
name：‘ZhangSan’
age:20
gender:‘M’
score:{Chinese:80, Math:90}
score_history:[85,82,88,90]

6. 删除某个参数

rosparam delete param_key

二、launch 文件载入param

1. 通过param 标签设置参数的值

<launch><param name="publish_frequency" value="20.0"/>
launch>

2. 通过加载yaml文件来设置param：
   下面这句指令也就是执行了 load 命令来实现装载文件的命令。

<launch><rosparam file="$(find robot_sim_demo)/param/xbot-u_control.yaml" command="load"/>
launch>

3. 加载URDF 文件
   下面这句指令是 xacro.py 执行了 robot.xacro 之后输出的结果作为值赋给 robot_description。

<launch><param name="robot_description" command="$(find xacro)/xacro.py $(find robot_sim_demo)/urdf/robot.xacro" />
launch>

launch 文件操作param 示例：

<launch><param name="param1" value="1" /><param name="param2" value="2" /><rosparam>   param3: 3param4: 4param5: 5rosparam><node pkg="param_demo" type="param_demo" name="param_demo" output="screen" >node>
launch>

三、c++ 中操作 param

#includeint main(int argc, char **argv){ros::init(argc, argv, "param_demo");ros::NodeHandle nh;int parameter1, parameter2, parameter3, parameter4, parameter5;//Get Param的三种方法//① ros::param::get()获取参数“param1”的value，写入到parameter1上bool ifget1 = ros::param::get("param1", parameter1);//② ros::NodeHandle::getParam()获取参数，与①作用相同bool ifget2 = nh.getParam("param2",parameter2);//③ ros::NodeHandle::param()类似于①和②//但如果get不到指定的param，它可以给param指定一个默认值(如33333)nh.param("param3", parameter3, 33333);//parameter3 = nh.param("param3", 33333); //这两种方式都可以获取参数if(ifget1)ROS_INFO("Get param1 = %d", parameter1);elseROS_WARN("Didn't retrieve param1");if(ifget2)ROS_INFO("Get param2 = %d", parameter2);elseROS_WARN("Didn't retrieve param2");if(nh.hasParam("param3"))ROS_INFO("Get param3 = %d", parameter3);elseROS_WARN("Didn't retrieve param3");//Set Param的两种方法//① ros::param::set()设置参数parameter4 = 4;ros::param::set("param4", parameter4);//② ros::NodeHandle::setParam()设置参数parameter5 = 5;nh.setParam("param5",parameter5);ROS_INFO("Param4 is set to be %d", parameter4);ROS_INFO("Param5 is set to be %d", parameter5);//Check Param的两种方法//① ros::NodeHandle::hasParam()bool ifparam5 = nh.hasParam("param5");//② ros::param::has()bool ifparam6 = ros::param::has("param6");if(ifparam5) ROS_INFO("Param5 exists");elseROS_INFO("Param5 doesn't exist");if(ifparam6) ROS_INFO("Param6 exists");elseROS_INFO("Param6 doesn't exist");//Delete Param的两种方法//① ros::NodeHandle::deleteParam()bool ifdeleted5 = nh.deleteParam("param5");//② ros::param::del()bool ifdeleted6 = ros::param::del("param6");if(ifdeleted5)ROS_INFO("Param5 deleted");elseROS_INFO("Param5 not deleted");if(ifdeleted6)ROS_INFO("Param6 deleted");elseROS_INFO("Param6 not deleted");ros::Rate rate(0.3);while(ros::ok()){int parameter = 0;ROS_INFO("=============Loop==============");//roscpp中尚未有ros::param::getallparams()之类的方法if(ros::param::get("param1", parameter))ROS_INFO("parameter param1 = %d", parameter);if(ros::param::get("param2", parameter))ROS_INFO("parameter param2 = %d", parameter);if(ros::param::get("param3", parameter))ROS_INFO("parameter param3 = %d", parameter);if(ros::param::get("param4", parameter))ROS_INFO("parameter param4 = %d", parameter);if(ros::param::get("param5", parameter))ROS_INFO("parameter param5 = %d", parameter);if(ros::param::get("param6", parameter))ROS_INFO("parameter param6 = %d", parameter);rate.sleep();}
}

按照这样的配置运行launch文件，输出结果为：

[ INFO] [1599227480.007106576]: Get param1 = 1
[ INFO] [1599227480.007183637]: Get param2 = 2
[ INFO] [1599227480.008421688]: Get param3 = 3
[ INFO] [1599227480.013664463]: Param4 is set to be 4
[ INFO] [1599227480.013728307]: Param5 is set to be 5
[ INFO] [1599227480.016448700]: Param5 exists
[ INFO] [1599227480.016485628]: Param6 doesn't exist
[ INFO] [1599227480.018160277]: Param5 deleted
[ INFO] [1599227480.018213034]: Param6 not deleted
[ INFO] [1599227480.018256838]: =============Loop==============
[ INFO] [1599227480.019019334]: parameter param1 = 1
[ INFO] [1599227480.019704553]: parameter param2 = 2
[ INFO] [1599227480.020431854]: parameter param3 = 3
[ INFO] [1599227480.021171333]: parameter param4 = 4
[ INFO] [1599227483.351733159]: =============Loop==============
[ INFO] [1599227483.354448047]: parameter param1 = 1
[ INFO] [1599227483.355546242]: parameter param2 = 2
[ INFO] [1599227483.356730625]: parameter param3 = 3
[ INFO] [1599227483.357654706]: parameter param4 = 4
.......

四、python 中操作 param

#!/usr/bin/env python
# coding:utf-8import rospydef param_demo():rospy.init_node("param_demo")rate = rospy.Rate(1)while(not rospy.is_shutdown()):#get paramparameter1 = rospy.get_param("/param1")parameter2 = rospy.get_param("/param2", default=222)rospy.loginfo('Get param1 = %d', parameter1)rospy.loginfo('Get param2 = %d', parameter2)#delete paramrospy.delete_param('/param2')#set paramrospy.set_param('/param2',2)#check paramifparam3 = rospy.has_param('/param3')if(ifparam3):rospy.loginfo('/param3 exists')else:rospy.loginfo('/param3 does not exist')#get all param namesparams = rospy.get_param_names()rospy.loginfo('param list: %s', params)rate.sleep()if __name__=="__main__":param_demo()

运行这个python脚本文件输出结果为：

[INFO] [1599227816.193803]: Get param1 = 1
[INFO] [1599227816.194120]: Get param2 = 2
[INFO] [1599227816.198019]: /param3 exists
[INFO] [1599227816.199841]: param list: ['/roslaunch/uris/host_wong_inspiron_3558__37695', '/rosversion', '/run_id', '/param5', '/param4', '/param3', '/param2', '/param1', '/rosdistro']
[INFO] [1599227817.197727]: Get param1 = 1
[INFO] [1599227817.199030]: Get param2 = 2
[INFO] [1599227817.208759]: /param3 exists
[INFO] [1599227817.211776]: param list: ['/roslaunch/uris/host_wong_inspiron_3558__37695', '/rosversion', '/run_id', '/param5', '/param4', '/param3', '/param2', '/param1', '/rosdistro']
........

五、操作 param 时注意命名空间

在 c++ 操作参数的时候，我们经常会看到
ros::NodeHandle nh; 和 ros::NodeHandle nh("~"); 两种用法。
主要是全局命名空间和局部命名空间的不同。
ros::NodeHandle nh; 是 全局命名空间，
ros::NodeHandle nh("~"); 是 局部命名空间。

<launch><param name="param1" value="1" /><param name="param2" value="2" /><node pkg="param_demo" type="param_demo" name="param_demo" output="screen" ><param name="param3" value="3" /><param name="param4" value="4" />node>
launch>

那么对应到cpp中，对于这两种param的获取方式有所不同：

#includeint main(int argc, char **argv){ros::init(argc, argv, "param_demo");ros::NodeHandle nh_global;ros::NodeHandle nh_local("~");int parameter1, parameter2, parameter3, parameter4;parameter1 = nh_global.param("param1", 1111);parameter3 = nh_global.param("param_demo/param3", 1111);	//获取局部参数，需要增加包名parameter2 = nh_local.param("/param2", 2222);	//获取全局参数，需要增加 "/""parameter4 = nh_local.param("param4", 2222);ROS_INFO("parameter param1 = %d", parameter1);ROS_INFO("parameter param2 = %d", parameter2);ROS_INFO("parameter param3 = %d", parameter3);ROS_INFO("parameter param4 = %d", parameter4);ros::spin();return 0;
}

按照这样的配置运行launch文件，输出结果为：

[ INFO] [1599231214.229291485]: parameter param1 = 1
[ INFO] [1599231214.229367939]: parameter param2 = 2
[ INFO] [1599231214.229398017]: parameter param3 = 3
[ INFO] [1599231214.229421101]: parameter param4 = 4

参考链接：
[1] 中科院软件所-机器人操作系统入门（ROS入门教程）- P15-4.2 Parammeter Server： https://www.bilibili.com/video/BV1mJ411R7Ni?p=15
[2] Changkun -github :https://github.com/sychaichangkun/ROS-Academy-for-Beginners

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