PoseArray not getting published

asked 2019-12-22 07:22:15 -0500

Parth2851
63 ●9 ●12 ●19

updated 2019-12-25 05:30:54 -0500

Hi, so I'm trying to find the shortest path from source to destination using dijkstra's algorithm.

In this program, I intend to first store the path in an array from which I retrieve it and publish it as a Pose Array. However, when I run this program I see no PoseArray topics.

I am trying to publish it from inside the dijkstra function.

#include <ros/ros.h>
#include <math.h>
#include <queue>
#include <vector>
#include <std_msgs/String.h>
#include <geometry_msgs/Pose.h>
#include <geometry_msgs/PoseArray.h>
#include <nav_msgs/OccupancyGrid.h>
#include <nav_msgs/GetMap.h>
#include <ros/console.h>
#define FMAX 999999999.99


    int rows = 1000, columns = 1000, size = rows * columns;
    bool visited[1000000];
    float distance[1000000];
    int prev[1000000];
    int source = 15100, destination = 990500; // Random source and destination
    .
    .
    .

    void dijkstra(const nav_msgs::OccupancyGrid& map)
    {
        prev[source] = 0;
        node first = {source, 0.0}; 
        pq.push(first);
        while(!pq.empty())
        {
            .
                    .
            int rr, cc;
            for(int i = 0; i < 8; i++) // to calculate neighbours
            {
                .
                            .
                            .
                .
            }
        }

        poseArray.poses = pose_vector;
        ros::NodeHandle n("~");
        ros::Publisher pose_array_pub = n.advertise<geometry_msgs::PoseArray>("/poseArray", 1);
        pose_array_pub.publish(poseArray);
    }



    int main(int argc, char **argv)
    {
        init();
        distance[source] = 0;
        visited[source] = true;
        ros::init(argc, argv, "dijkstra");
        ros::NodeHandle n("~");
        ros::ServiceClient client = n.serviceClient<nav_msgs::GetMap>("/static_map");
        nav_msgs::OccupancyGrid my_map = srv.response.map;
        dijkstra(my_map);
        ros::spin();    
    }

EDIT - Deleted parts of my code to make the question more relevant.

answered 2019-12-22 08:14:52 -0500

gvdhoorn
86574 ●283 ●1432 ●1054 http://cor.tudelft.nl/

updated 2019-12-23 07:12:57 -0500

We see this:

void dijkstra(const nav_msgs::OccupancyGrid& map)
{
  ...

  ros::NodeHandle n("~");
  ros::Publisher pose_array_pub = n.advertise<geometry_msgs::PoseArray>("/poseArray", 1);
  pose_array_pub.publish(poseArray);
}

Never create NodeHandles, ros::Publisher or ros::Subscribers in the body of callbacks or in short-lived functions.

It will not work.

Also never call publish(..) immediately after constructing a ros::Publisher. There is no time for Subscribers to actually subscribe, so no one receives your message.

Create them in your main(..) and pass them to your callback. Or create them as global variables or create a class and store them as members.

Then if you're only publishing the message once, make sure there are subscribers. You can use ros::Publisher::getNumSubscribers() for this. But if only publishing once and it's important your message always arrives, then I would suggest to use a service instead of a topic.

Edit:

Okay, yes. I made a publisher in mainand then I declared a global poseArray and then published it in a loop something like this -
while(ros::ok())
{
  pose_array_pub.publish(pa);
}

I would strongly recommend you do not do this. For two reasons (at least):

you're not publishing many, many old messages as pa is not updated before publish(..) is called
if this is the exact code you used: you're publishing at the maximum rate at which your PC can publish (which for a typical PC is upwards of 10kHz)

What I was actually suggesting was something like this:

#include <ros/ros.h>

...

ros::Publisher pub;   // note: in global scope here

...

void dijkstra(const nav_msgs::OccupancyGrid& map)
{
  ...

  // use variable in global scope
  pub.publish(poseArray);
}


int main(int argc, char **argv)
{
  ros::init(argc, argv, "dijkstra");
  ros::NodeHandle n("~");
  ...

  // initialise variable in global scope
  pub = n.advertise<geometry_msgs::PoseArray>("/poseArray", 1);

  ...
  ros::spin();
}

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Comments

PS: yes, this is software, so "never" is never really never, but if you're just starting out with all of this, you should really not do this.

gvdhoorn ( 2019-12-22 08:15:44 -0500 )edit

This worked! thanks!

Parth2851 ( 2019-12-22 12:32:58 -0500 )edit

For future readers: what worked, specifically?

gvdhoorn ( 2019-12-23 03:03:11 -0500 )edit

Okay, yes. I made a publisher in mainand then I declared a global poseArray and then published it in a loop something like this -

while(ros::ok())
        {
            pose_array_pub.publish(pa);
        }

Parth2851 ( 2019-12-23 04:37:26 -0500 )edit

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