Build error : undefined reference to `cv_bridge::CvImage::toImageMsg() const' - c++

Question

I am using ROS Kinetic and trying to write a program that would read two videos and publish them on two different topics. But I think I've made some mistake in linking OpenCV libraries. I am getting the following errors.
CMakeFiles/src.dir/src/src.cpp.o: In function `main':
src.cpp:(.text+0x3fd): undefined reference to `cv_bridge::CvImage::toImageMsg() const'
src.cpp:(.text+0x56d): undefined reference to `cv_bridge::CvImage::toImageMsg() const'
collect2: error: ld returned 1 exit status
MultiCamImages/CMakeFiles/src.dir/build.make:165: recipe for target 'MultiCamImages/src' failed
make[2]: *** [MultiCamImages/src] Error 1
CMakeFiles/Makefile2:1089: recipe for target 'MultiCamImages/CMakeFiles/src.dir/all' failed
make[1]: *** [MultiCamImages/CMakeFiles/src.dir/all] Error 2
Makefile:138: recipe for target 'all' failed
make: *** [all] Error 2
Invoking "make -j4 -l4" failed
This is my source file:
#include <ros/ros.h>
#include <cv_bridge/cv_bridge.h>
#include <image_transport/image_transport.h>
#include <sensor_msgs/image_encodings.h>
#include <opencv2/opencv.hpp>
#include <iostream>
#include <fstream>
using namespace std;
int main(int argc, char** argv){
ros::init(argc, argv, "PublishMultiCamImages");
ros::NodeHandle nh;
image_transport::ImageTransport it(nh);
image_transport::Publisher pub1 = it.advertise("/camera/image_raw1", 1);
image_transport::Publisher pub2 = it.advertise("/camera/image_raw2", 1);
cv::Mat im;
cv::String Path1("/home/akanksha/COSLAM_Dataset/EA-01/grayscale/*.jpg");
cv::String Path2("/home/akanksha/COSLAM_Dataset/EA-02/grayscale/*.jpg");
//time = ros::Time::now();
vector<cv::String> fn1;
vector<cv::String> fn2;
cv::glob(Path1,fn1, true); // recurse
cv::glob(Path2,fn2, true);
ros::Rate r(50);
int l1 = fn1.size();
int l2 = fn2.size();
int count1 = 0, count2 = 0;
bool flag;
while(ros::ok()){
flag = true;
if(count1 < l1){
cv::Mat image1 = cv::imread(fn1[count1]);
sensor_msgs::ImagePtr msg1 = cv_bridge::CvImage(std_msgs::Header(), "bgr8", image1).toImageMsg();
pub1.publish(msg1);
count1++;
flag = false;
}
if(count2 < l2){
cv::Mat image2 = cv::imread(fn2[count2]);
sensor_msgs::ImagePtr msg2 = cv_bridge::CvImage(std_msgs::Header(), "bgr8", image2).toImageMsg();
pub2.publish(msg2);
count2++;
flag = false;
}
if(flag)
break;
r.sleep();
}
ros::shutdown();
return 0;
}
This is my CMakeLists.txt
cmake_minimum_required(VERSION 2.8.3)
project(MultiCamImages)
find_package(catkin REQUIRED COMPONENTS
roscpp
image_transport
OpenCV
)
# find_package(OpenCV REQUIRED)
set(OpenCV_LIBS opencv_core opencv_imgproc opencv_calib3d opencv_video opencv_features2d opencv_ml opencv_highgui opencv_objdetect)
add_executable(src src/src.cpp)
target_link_libraries(src ${catkin_LIBRARIES} ${OpenCV_LIBS})
catkin_package(
# INCLUDE_DIRS include
# LIBRARIES MultiCamImages
# CATKIN_DEPENDS roscpp
# DEPENDS system_lib
)
include_directories(
${catkin_INCLUDE_DIRS}
)
And this is my pakage.xml
<?xml version="1.0"?>
<package>
<name>MultiCamImages</name>
<version>0.0.0</version>
<description>The MultiCamImages package</description>
<maintainer email="akanksha#todo.todo">akanksha</maintainer>
<buildtool_depend>catkin</buildtool_depend>
<build_depend>roscpp</build_depend>
<run_depend>roscpp</run_depend>
<build_depend>sensor_msgs</build_depend>
<run_depend>sensor_msgs</run_depend>
<build_depend>cv_bridge</build_depend>
<run_depend>cv_bridge</run_depend>
</package>
If you could point out the problem that would be a great help. Thanks!

Answer 1

It doesn't look like you are linking cv_bridge in the cmake file. Maybe you want this:
find_package(catkin REQUIRED COMPONENTS
cv_bridge
roscpp
image_transport
OpenCV
)

Answer 2

Actually the way Joseph uses OpenCV libraries for linking is not right, since OpenCV does not belong to the standard package of ROS as with cv_bridge. In this case, you need to separately use find_package for OpenCV as with boost like this:
find_package(OpenCV REQUIRED)
# Or you may add specific major portion of OpenCV version, e.g., OpenCV3
find_package(OpenCV 3 REQUIRED)