ROS with V-rep (2) (ROS學習筆記五）

昨晚完成了將ROS與V-rep的橋接，雖然沒有讀出有效消息，但已經從rostopic中看到了相應的ropic出現，今天經過簡單的調試，果然可以實現對V-rep中的消息在ROS中的接收與發送。

一、在V-rep中創建ROS話題

接着昨天的工作，仔細研究LUA中的函數參數後修改昨天的LUA代碼中的那三行如下：

sensorPub = simExtROS_enablePublisher('/frontUS',1000,simros_strmcmd_read_proximity_sensor,hFrontUS,-1,'std_msgs/Float64')

rightPub = simExtROS_enableSubscriber('/right_cmd',1000,simros_strmcmd_set_joint_target_velocity,hRightMotor,-1,'std_msgs/Float64')

leftPub = simExtROS_enableSubscriber('/left_cmd',1000,simros_strmcmd_set_joint_target_velocity,hRightMotor,-1,'std_msgs/Float64')

以上三個函數其實就是整個工程搭橋的核心部分了，這三個函數不論是從函數名還是參數上都比較難搞，經過一番研究我理解的如下：

sensorPub等號前面的其實只是一個在Vrep中的變量，隨便命名不影響在ROS中的調用。

三個函數的第一個參數即爲需要發送/接收的話題名稱，如果沒有這個話題，進程便會在ROS中建立一個話題，並向其中發送/接收消息，

第二個參數爲消息隊列，在這裏如果消息頻率沒有問題則問題不大。

第三個參數最爲重要，意味着V-rep以什麼消息類型去接收/發送消息，這裏其實需要的是一個number型參數，但V-rep中已經定義好了一些變量，如“simros_strmcmd_set_joint_target_velocity”就是一個stdmsg::Float64 型參數，於是他創建的話題中需要去接收這樣一個消息，來控制輪子的轉動。

第四個參數決定了將接收到的消息傳送給V-rep中的哪個部件，這個參數就是之前從V-rep中get到的Handle，這樣就可以將目標handle 與ROS話題鏈接起來

第五個參數參考上篇中的最後一個參考資料，如果不需要則爲-1。

第六個參數目前我還沒有搞得很清楚，似乎是一個字符串就可以正常運行，不知道具體用在哪裏，但不影響運行。

二、在ROS中讀取消息

有了（一）中的工作，我們其實topic中已經有傳感器的輸出與等待輸入的topic了。

我們固然可以直接rostopic pub來控制兩輪轉速，但對proximity 的讀取則無法直接echo出來，因爲我們並沒有定義這個消息類型，這是需要找到Vrep_common/Pro...Data.msg，將其複製到我們自己工作區中創建的msg文件夾中，然後修改CMakeList與package文件，具體可以參考以下內容：

爲了更好的控制，我寫了一個myrobot_control.cpp來控制小車轉動，代碼如下：

#include<ros/ros.h>
#include<string>
#include "std_msgs/Float64.h"
#include "geometry_msgs/Twist.h"

using namespace std;

int main(int argc, char** argv){
	ros::init(argc, argv, "controller");
	ros::NodeHandle n;
	
	ros::Publisher leftwheel_pub = n.advertise<std_msgs::Float64>("left_vel",1000);
	ros::Publisher rightwheel_pub = n.advertise<std_msgs::Float64>("right_vel",1000);

	ros::Rate loop_rate(1);

	int count = 0;
	std_msgs::Float64 left_velocity,right_velocity;	
	left_velocity.data = right_velocity.data = 0;
	
	while(ros::ok()){
	   	count++;
		if(count >= 5) count = 0;
		left_velocity.data = count;
		right_velocity.data = -count;
		
		leftwheel_pub.publish(left_velocity);
		rightwheel_pub.publish(right_velocity);

		ros::spinOnce();
		loop_rate.sleep();
	}
	return 0;
}

同時配置CMakeList如下：

cmake_minimum_required(VERSION 2.8.3)
project(vrep_common)

## Add support for C++11, supported in ROS Kinetic and newer
# add_definitions(-std=c++11)

## Find catkin macros and libraries
## if COMPONENTS list like find_package(catkin REQUIRED COMPONENTS xyz)
## is used, also find other catkin packages
find_package(catkin REQUIRED COMPONENTS roscpp rospy std_msgs geometry_msgs message_generation)

## System dependencies are found with CMake's conventions
# find_package(Boost REQUIRED COMPONENTS system)


## Uncomment this if the package has a setup.py. This macro ensures
## modules and global scripts declared therein get installed
## See http://ros.org/doc/api/catkin/html/user_guide/setup_dot_py.html
# catkin_python_setup()

################################################
## Declare ROS messages, services and actions ##
################################################

## To declare and build messages, services or actions from within this
## package, follow these steps:
## * Let MSG_DEP_SET be the set of packages whose message types you use in
##   your messages/services/actions (e.g. std_msgs, actionlib_msgs, ...).
## * In the file package.xml:
##   * add a build_depend tag for "message_generation"
##   * add a build_depend and a run_depend tag for each package in MSG_DEP_SET
##   * If MSG_DEP_SET isn't empty the following dependency has been pulled in
##     but can be declared for certainty nonetheless:
##     * add a run_depend tag for "message_runtime"
## * In this file (CMakeLists.txt):
##   * add "message_generation" and every package in MSG_DEP_SET to
##     find_package(catkin REQUIRED COMPONENTS ...)
##   * add "message_runtime" and every package in MSG_DEP_SET to
##     catkin_package(CATKIN_DEPENDS ...)
##   * uncomment the add_*_files sections below as needed
##     and list every .msg/.srv/.action file to be processed
##   * uncomment the generate_messages entry below
##   * add every package in MSG_DEP_SET to generate_messages(DEPENDENCIES ...)

## Generate messages in the 'msg' folder
 add_message_files(
   FILES
   ProximitySensorData.msg
#   Message1.msg
#   Message2.msg
 )

## Generate services in the 'srv' folder
# add_service_files(
#   FILES
#   Service1.srv
#   Service2.srv
# )

## Generate actions in the 'action' folder
# add_action_files(
#   FILES
#   Action1.action
#   Action2.action
# )

## Generate added messages and services with any dependencies listed here
 generate_messages(
   DEPENDENCIES
   std_msgs  # Or other packages containing msgs
   geometry_msgs
 )

################################################
## Declare ROS dynamic reconfigure parameters ##
################################################

## To declare and build dynamic reconfigure parameters within this
## package, follow these steps:
## * In the file package.xml:
##   * add a build_depend and a run_depend tag for "dynamic_reconfigure"
## * In this file (CMakeLists.txt):
##   * add "dynamic_reconfigure" to
##     find_package(catkin REQUIRED COMPONENTS ...)
##   * uncomment the "generate_dynamic_reconfigure_options" section below
##     and list every .cfg file to be processed

## Generate dynamic reconfigure parameters in the 'cfg' folder
# generate_dynamic_reconfigure_options(
#   cfg/DynReconf1.cfg
#   cfg/DynReconf2.cfg
# )

###################################
## catkin specific configuration ##
###################################
## The catkin_package macro generates cmake config files for your package
## Declare things to be passed to dependent projects
## INCLUDE_DIRS: uncomment this if you package contains header files
## LIBRARIES: libraries you create in this project that dependent projects also need
## CATKIN_DEPENDS: catkin_packages dependent projects also need
## DEPENDS: system dependencies of this project that dependent projects also need
#catkin_package(
#  INCLUDE_DIRS include
#  LIBRARIES vrep_common
#  CATKIN_DEPENDS other_catkin_pkg
#  DEPENDS system_lib
#)
catkin_package(
  LIBRARIES vrep_common
  CATKIN_DEPENDS message_runtime roscpp rospy std_msgs geometry_msgs 
  DEPENDS system_lib
  )
###########
## Build ##
###########

## Specify additional locations of header files
## Your package locations should be listed before other locations
# include_directories(include)

## Declare a C++ library
# add_library(${PROJECT_NAME}
#   src/${PROJECT_NAME}/vrep_common.cpp
# )

## Add cmake target dependencies of the library
## as an example, code may need to be generated before libraries
## either from message generation or dynamic reconfigure
# add_dependencies(${PROJECT_NAME} ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS})

## Declare a C++ executable
## With catkin_make all packages are built within a single CMake context
## The recommended prefix ensures that target names across packages don't collide
# add_executable(${PROJECT_NAME}_node src/vrep_common_node.cpp)

## Rename C++ executable without prefix
## The above recommended prefix causes long target names, the following renames the
## target back to the shorter version for ease of user use
## e.g. "rosrun someones_pkg node" instead of "rosrun someones_pkg someones_pkg_node"
# set_target_properties(${PROJECT_NAME}_node PROPERTIES OUTPUT_NAME node PREFIX "")

## Add cmake target dependencies of the executable
## same as for the library above
# add_dependencies(${PROJECT_NAME}_node ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS})

## Specify libraries to link a library or executable target against
# target_link_libraries(${PROJECT_NAME}_node
#   ${catkin_LIBRARIES}
# )

#############
## Install ##
#############

# all install targets should use catkin DESTINATION variables
# See http://ros.org/doc/api/catkin/html/adv_user_guide/variables.html

## Mark executable scripts (Python etc.) for installation
## in contrast to setup.py, you can choose the destination
# install(PROGRAMS
#   scripts/my_python_script
#   DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION}
# )

## Mark executables and/or libraries for installation
# install(TARGETS ${PROJECT_NAME} ${PROJECT_NAME}_node
#   ARCHIVE DESTINATION ${CATKIN_PACKAGE_LIB_DESTINATION}
#   LIBRARY DESTINATION ${CATKIN_PACKAGE_LIB_DESTINATION}
#   RUNTIME DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION}
# )

## Mark cpp header files for installation
# install(DIRECTORY include/${PROJECT_NAME}/
#   DESTINATION ${CATKIN_PACKAGE_INCLUDE_DESTINATION}
#   FILES_MATCHING PATTERN "*.h"
#   PATTERN ".svn" EXCLUDE
# )

## Mark other files for installation (e.g. launch and bag files, etc.)
# install(FILES
#   # myfile1
#   # myfile2
#   DESTINATION ${CATKIN_PACKAGE_SHARE_DESTINATION}
# )

#############
## Testing ##
#############

## Add gtest based cpp test target and link libraries
# catkin_add_gtest(${PROJECT_NAME}-test test/test_vrep_common.cpp)
# if(TARGET ${PROJECT_NAME}-test)
#   target_link_libraries(${PROJECT_NAME}-test ${PROJECT_NAME})
# endif()

## Add folders to be run by python nosetests
# catkin_add_nosetests(test)
include_directories (include ${catkin_INCLUDE_DIRS})
add_executable(vrep_common myrobot_control.cpp)
target_link_libraries(vrep_common ${catkin_LIBRARIES})

package如下：

<?xml version="1.0"?>
<package>
  <name>vrep_common</name>
  <version>0.0.0</version>
  <description>The vrep_common package</description>

  <!-- One maintainer tag required, multiple allowed, one person per tag --> 
  <!-- Example:  -->
  <!-- <maintainer email="[email protected]">Jane Doe</maintainer> -->
  <maintainer email="[email protected]">jkwang</maintainer>


  <!-- One license tag required, multiple allowed, one license per tag -->
  <!-- Commonly used license strings: -->
  <!--   BSD, MIT, Boost Software License, GPLv2, GPLv3, LGPLv2.1, LGPLv3 -->
  <license>TODO</license>


  <!-- Url tags are optional, but multiple are allowed, one per tag -->
  <!-- Optional attribute type can be: website, bugtracker, or repository -->
  <!-- Example: -->
  <!-- <url type="website">http://wiki.ros.org/vrep_common</url> -->


  <!-- Author tags are optional, multiple are allowed, one per tag -->
  <!-- Authors do not have to be maintainers, but could be -->
  <!-- Example: -->
  <!-- <author email="[email protected]">Jane Doe</author> -->


  <!-- The *_depend tags are used to specify dependencies -->
  <!-- Dependencies can be catkin packages or system dependencies -->
  <!-- Examples: -->
  <!-- Use build_depend for packages you need at compile time: -->
  <!--   <build_depend>message_generation</build_depend> -->
  <!-- Use buildtool_depend for build tool packages: -->
  <!--   <buildtool_depend>catkin</buildtool_depend> -->
  <!-- Use run_depend for packages you need at runtime: -->
  <!--   <run_depend>message_runtime</run_depend> -->
  <!-- Use test_depend for packages you need only for testing: -->
  <!--   <test_depend>gtest</test_depend> -->
  <buildtool_depend>catkin</buildtool_depend>
  <build_depend>message_generation</build_depend>
  <build_depend>roscpp</build_depend>
  <build_depend>rospy</build_depend>
  <build_depend>std_msgs</build_depend>
  <build_depend>geometry_msgs</build_depend>

  <run_depend>message_runtime</run_depend>
  <run_depend>roscpp</run_depend>
  <run_depend>rospy</run_depend>
  <run_depend>std_msgs</run_depend>
  <run_depend>geometry_msgs</run_depend>  
	<!-- The export tag contains other, unspecified, tags -->
  <export>
    <!-- Other tools can request additional information be placed here -->

  </export>
</package>

至此應該可以echo出傳感器的信息，並且實現控制小車逐漸變快的轉動了。

注：爲了保證V-rep對消息類型的要求得到滿足，建議將rospkg的名字改爲vrep_common ,省去了在V-rep中進一步修改其他地方的煩惱。

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