Working with compressed image transport

[fabioperez]

I'm trying to use a compressed image transport with ros_opentld. I changed the project to work with image_transport, which can handle compressed images.

I've made the following modifications to the project: main.hpp:

• added #include <image_transport/image_transport.h>
• changed sub1 = n.subscribe("image", 1000, &Main::imageReceivedCB, this); to

image_transport::ImageTransport it( n );
sub1 = it.subscribe("image", 1000, &Main::imageReceivedCB, this );

• changed ros::Subscriber sub1 to image_transport::Subscriber sub1;.

base_frame.hpp:

• changed ros::Subscriber sub1; to image_transport::Subscriber sub1;

base_frame.cpp:

• added #include <image_transport/image_transport.h>changed
• changed sub1 = n.subscribe("image", 1000, &BaseFrame::image_receivedCB, this); to

image_transport::ImageTransport it( n );
sub1 = it.subscribe("image", 1000, &BaseFrame::image_receivedCB, this );

In both launch files I added: <remap from="image/compressed" to="$(arg image_topic)/compressed"/>.

I also changed the default image topic to my camera. Then I run the tracker (tracker/gui in two terminal tabs):

roslaunch tld_tracker ros_tld_tracker.launch _image_transport:=compressed
roslaunch tld_tracker ros_tld_tracker.launch _image_transport:=compressed

I can see the image from the camera within the GUI window, update with F5, select a box, press ENTER, but the tracking is not working.

When enter is pressed, the following message is echoed: [ INFO] [1387170673.023733280]: Bounding Box received.

I've also tried auto_face_detection:=true, but it's not working either.

[Ronan0912]

You need to subscribe to the base image topic and not a specific image_transport topic.

I quote from ROS wiki: "The actual ROS topic subscribed to depends on which transport is used." and "typically you should not directly reference the transport-specific topic used by a particular plugin."

In order to select a specific transport, you have to add hints : image_transport::TransportHints hints("name_of_the_plugin", ros::TransportHints()); sub1 = n.subscribe("image", 1000, &Main::imageReceivedCB, this, hints);

[fabioperez]

I've tried what you suggested, but I'm getting this error:

main.hpp:85:70: error: no matching function for call to ‘ros::NodeHandle::subscribe(const char [6], int, void (Main::*)(const ImageConstPtr&), Main* const, image_transport::TransportHints&)’

The GUI node is subscribing to the correct compressed camera topic (it's showing the images), but the tracker node is subscribing to the topic without the /compressed. Maybe it's because /ros_tld_tracker_node receives the _image_transport:=compressed argument but the main_node cannot see it.

[Ronan0912]

I made a mistake, it's it.subscribe(...); not n.subscribe(...);. It's specified in the ROS documentation that the base_topic have to be used and the transport need to be set by the image_transport parameter or the hints. Indeed, it could be an issue with the nodehandles. You can try to instantiate the image_transport object with the private nodehandle used to get all the parameters in the constructor.

[fabioperez]

It's now working. I wasn't adding <remap from="image/compressed" to="$(arg image_topic)/compressed"/> to ros_tld_tracker.launch. However, this remap workaround is not elegant at all.

I added the hints but they were not necessary for the program to work. The full modified code is in my fork.