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take from LCM and ROS, send to LCM

asked 2015-09-23 06:26:21 -0500

mark_vision gravatar image

Hi all, I need to interface ROS and LCM.

I thought to do in the following way: I have a class. Let's call it MyClass I have an LCM callback that I use to fill a class variable. Lets call it MyClass::lcm_cb(); I have a ROS callback that I use to do my processing. Let's call it MyClass::ros_cb();

Actually the ROS callback is a synchronized callback that takes from two topics via message_filter.

I need process the data from the ROS message. As soon as I receive the ROS message, I want to get the last available message from LCM, invoking MyClass::lcm_cb(), and use it together with the ROS message. Then I want to publish on LCM again something.

I want that what dictates the frequency is ROS and not LCM. My pseudocode is something like this:

MyClass::MyClass(ros::NodeHandle& nh) : nh_(nh) {
    sync = new message_filters::Synchronizer<MySyncPolicy> (MySyncPolicy(10), first_sub, second_sub);
    sync->registerCallback(boost::bind(&MyClass::ros_cb, this, _1, _2));
    lcm_sub = mylcm.subscribe("LCM_TOPIC", MyClas::lcm_cb, this);
}

MyClass::ros_cb(const sensor_msgs::ImageConstPtr& depth_input,
    const sensor_msgs::PointCloud2ConstPtr& cloud_input) {
    // INVOKE LCM CALLBACK
    mylcm.handle();
    // DO STUFF
    mylcm.publish("LCM_OUTPUT", &out_msg_);
}


void MyClass::lcm_cb(const lcm::ReceiveBuffer *rbuf,
        const string &chan,
        const mav::pose_t *msg) {
     // DO OTHER STUFF
}

MyClass::run() {
    ros::spin();
}

int main(int argc, char **argv) {
    ros::init(argc, argv, "my_node");
    ros::NodeHandle nh;
    MyClass mc(nh);
    mc.run();
}

If I run it, apparently the ROS callback is not called or it gets stuck forever after the first call.

What is wrong?

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answered 2015-09-23 06:35:04 -0500

updated 2015-09-23 16:30:21 -0500

I'm not sure what is wrong with your code, but you might want to take a look at the Pronto LCM<->ROS translators. I have used those and know they work, so you should be able to find out the issue by comparing them with your code.

/edit: Update as per your comment below. I'm not sure why things don't work as is, but what you could try is alternating ros::spin and lcm's handle in your run loop so their callbacks are always triggered:

void MyClass::lcm_cb(const lcm::ReceiveBuffer *rbuf,
        const string &chan,
        const mav::pose_t *msg) {
     // SAVE LCM DATA TO CLASS MEMBER SO IT'S ACCESSIBLE IN ROS CALLBACK
}

MyClass::run() {

  LOOP_WITH_RATE
  {
    mylcm.handle();
    ros::spinOnce();
  }
}
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I already know LCM ROS translators. They just listen to ROS and publish to LCM or the other way round. Here I want to listen both from LCM and ROS and to publish on LCM. It's a different issue. Thanks for the suggestion though.

mark_vision gravatar image mark_vision  ( 2015-09-23 07:39:18 -0500 )edit

Oh ok, I see. Updated with a suggestion of what you could try.

Stefan Kohlbrecher gravatar image Stefan Kohlbrecher  ( 2015-09-23 16:31:11 -0500 )edit

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Asked: 2015-09-23 06:26:21 -0500

Seen: 1,329 times

Last updated: Sep 23 '15