using image transport compression and boost library c++

Question

I have a callback that I need to run after subscribing to a ROS image topic:

void imageCallback(const sensor_msgs::ImageConstPtr& original_image, int n) {
   ..
}

as you can see, the callback takes two parameters, the image and a number. I know that is possible to use boost library to send two parameters to the callback in this way:

image_transport::Subscriber sub = it.subscribe("/camera1/RGB", 1, boost::bind(imageCallback,_1, 1));

but I would like to use also a compression transport plug-in. So, if I write

 image_transport::Subscriber sub = it.subscribe("/camera1/RGB", 1, boost::bind(imageCallback, _1, 1),image_transport::TransportHints::TransportHints("compressed"));

I cannot build the code:

error: no matching function for call to ‘image_transport::ImageTransport::subscribe(const char [13], int, boost::_bi::bind_t<void, void (*)(const sensor_msgs::ImageConstPtr&, int), boost::_bi::list2<boost::arg<1>, boost::_bi::value<int> > >, image_transport::TransportHints)’
/opt/ros/fuerte/stacks/image_common/image_transport/include/image_transport/image_transport.h:40: note: candidates are: image_transport::Subscriber image_transport::ImageTransport::subscribe(const std::string&, uint32_t, const boost::function<void(const sensor_msgs::ImageConstPtr&)>&, const ros::VoidPtr&, const image_transport::TransportHints&)
/opt/ros/fuerte/stacks/image_common/image_transport/include/image_transport/image_transport.h:48: note:                 image_transport::Subscriber image_transport::ImageTransport::subscribe(const std::string&, uint32_t, void (*)(const sensor_msgs::ImageConstPtr&), const image_transport::TransportHints&)

So, how I should write the subscriber line code? Thanks

Answer 1

Looks like you need to use this overload:

Subscriber image_transport::ImageTransport::subscribe(
        const std::string &     base_topic, 
        uint32_t                queue_size, 
        const boost::function<void(const sensor_msgs::ImageConstPtr &)>& callback, 
        const ros::VoidPtr &    tracked_object = ros::VoidPtr(), 
        const TransportHints &  transport_hints = TransportHints()
        )

So I'd assume you just need to explicitely pass the tracked_object parameter:

image_transport::Subscriber sub = it.subscribe(
    "/camera1/RGB", 
    1, 
    boost::bind(imageCallback, _1, 1),
    ros::VoidPtr(),                       // THIS ADDED
    image_transport::TransportHints::TransportHints("compressed")
);

(You might very well be able to just pass nullptr or NULL or 0 instead. I have no experience with the libraries shown here.)