ROS Custom message with sensor_msgs/Image Publisher - ros

Question

I have a custom .msg file MyImage.msg
sensor_msgs/Image im
float32 age
string name
I have configured the custom .msg fle as illustrated in link:CreatingMsgAndSrv
Further, I am trying to write a simple publisher with this msg.
#include <ros/ros.h>
#include <custom_msg/MyImage.h>
#include <image_transport/image_transport.h>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/opencv.hpp>
#include <cv_bridge/cv_bridge.h>
int main( int argc, char ** argv )
{
ros::init(argc, argv, "publish_custom");
ros::NodeHandle nh;
ros::Publisher pub2 = nh.advertise<custom_msg::MyImage>("custom_image", 2 );
cv::Mat image = cv::imread( "Lenna.png", CV_LOAD_IMAGE_COLOR );
sensor_msgs::ImagePtr im_msg = cv_bridge::CvImage(std_msgs::Header(), "bgr8", image).toImageMsg();
ros::Rate rate( 2 );
while( ros::ok() )
{
ROS_INFO_STREAM_ONCE( "IN main loop");
custom_msg::MyImage msg2;
msg2.age=54.3;
msg2.im = im_msg;
msg2.name="Gena";
pub2.publish(msg2);
rate.sleep();
}
}
This does not seem to compile with catkin_make. The error messages are -
/home/eeuser/ros_workspaces/HeloRosProject/src/custom_msg/publish.cpp: In function ‘int main(int, char**)’:
/home/eeuser/ros_workspaces/HeloRosProject/src/custom_msg/publish.cpp:40:19: error: no match for ‘operator=’ in ‘msg2.custom_msg::MyImage_<std::allocator<void> >::im = im_msg’
/home/eeuser/ros_workspaces/HeloRosProject/src/custom_msg/publish.cpp:40:19: note: candidate is:
/opt/ros/hydro/include/sensor_msgs/Image.h:56:8: note: sensor_msgs::Image_<std::allocator<void> >& sensor_msgs::Image_<std::allocator<void> >::operator=(const sensor_msgs::Image_<std::allocator<void> >&)
/opt/ros/hydro/include/sensor_msgs/Image.h:56:8: note: no known conversion for argument 1 from ‘sensor_msgs::ImagePtr {aka boost::shared_ptr<sensor_msgs::Image_<std::allocator<void> > >}’ to ‘const sensor_msgs::Image_<std::allocator<void> >&’
make[2]: *** [custom_msg/CMakeFiles/publish.dir/publish.cpp.o] Error 1
make[1]: *** [custom_msg/CMakeFiles/publish.dir/all] Error 2
make: *** [all] Error 2
Invoking "make" failed
I can understand that msg2.im = im_msg; isn't correct. Please help me fix this.

Answer 1

You are trying to assign a sensor_msgs::ImagePtr (a pointer) to a sensor_msgs::Image field. Simply you can't. Just look at the fifth line of your error log:
no known conversion for argument 1 from ‘sensor_msgs::ImagePtr {aka boost::shared_ptr<sensor_msgs::Image_<std::allocator<void> > >}’ to ‘const sensor_msgs::Image_<std::allocator<void> >&’
To solve this simple issue, just add the dereference operator (*) to that pointer:
msg2.im = *im_msg;
I assume that there are no other errors in the code.