用ROS调用cv_bridge的时候，报了个错，如下：

undefined reference to `cv_bridge::toCvCopy(boost::shared_ptr<sensor_msgs::Image_<std::allocator > const> const&, std::__cxx11::basic_string<char, std::char_traits, std::allocator > const&)’

意思就是我用的这个cv_bridge::toCvCopy函数没有定义，虽然我在开头已经include了对应的库，如：

#include <ros/ros.h>
#include <image_transport/image_transport.h>
#include <cv_bridge/cv_bridge.h>
#include <sensor_msgs/image_encodings.h>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>
#include<iostream>

但是其实还不行，需要在CMakeLists.txt里面也加入对应的cv_bridge package去编译才行：

...
find_package(Eigen3 REQUIRED)
find_package(PCL 1.8 REQUIRED)
find_package(OpenCV REQUIRED)

find_package(catkin REQUIRED COMPONENTS 
nav_msgs 
roscpp 
rospy 
serial 
tf 
std_msgs 
std_srvs 
actionlib
actionlib_msgs
message_generation
geometry_msgs
pcl_conversions
pcl_ros 
cv_bridge
)

...

add_executable(Frustum src/Frustum.cpp)
target_link_libraries(Frustum ${PCL_LIBRARIES} ${OpenCV_LIBRARIES} ${catkin_LIBRARIES} ${EIGEN3_LIBS})

所以在find_package里面加入cv_bridge就可以了，有的blog 说需要在xml文件了也加，我现在没加好像也没有什么问题。