ROSERROR : undefined reference to cv_bridge::toCvCopy

解决办法：参考原文

重新表述：

创建一个ROS功能包，完成主要功能会使用到opencv

下面是package.xml

  <buildtool_depend>catkin</buildtool_depend>
  <build_depend>roscpp</build_depend>
  <build_depend>rospy</build_depend>
  <build_depend>std_msgs</build_depend>
  <build_depend>cv_bridge</build_depend>
  <build_export_depend>roscpp</build_export_depend>
  <build_export_depend>rospy</build_export_depend>
  <build_export_depend>std_msgs</build_export_depend>
  <build_export_depend>cv_bridge</build_export_depend>
  <exec_depend>roscpp</exec_depend>
  <exec_depend>rospy</exec_depend>
  <exec_depend>std_msgs</exec_depend>
  <exec_depend>cv_bridge</exec_depend>
  <exec_depend>image_transport</exec_depend>

 CMakeLists.txt

cmake_minimum_required(VERSION 3.0.2)
project(line_follower)

find_package(catkin REQUIRED COMPONENTS
  roscpp
  rospy
  std_msgs
  genmsg 
  geometry_msgs
  message_generation
  image_transport
  cv_bridge
)

find_package(OpenCV )


## Generate messages in the 'msg' folder
 add_message_files(
   FILES
   pos.msg
)

## Generate added messages and services with any dependencies listed here
generate_messages(
   DEPENDENCIES
   std_msgs
 )

include_directories(include ${catkin_INCLUDE_DIRS})
include_directories(${OpenCV_INCLUDE_DIRS})

add_executable(detect src/detect.cpp src/linedetect.cpp)
target_link_libraries(detect ${catkin_LIBRARIES} ${OpenCV_LIBS})
add_dependencies(detect line_follower_generate_messages_cpp)

把这些写完整之后，编译通过了