Subscriber frequency by ros::spinOnce()

asked 2020-03-24 07:33:54 -0500

Kyuhwan Yeon gravatar image

My problem: Frequency of subscription does not change by ros::Rate

As I know, the frequency of subscription is changed by ros::Rate if i use ros::spinOnce()

Here is my code

#include <ros/ros.h>
#include <visualization_msgs/Marker.h>
#include "nav_msgs/Odometry.h"

float pickUpPos[3] = {3, 4, 1};
float dropOffPos[3] = {-1, 0, 1};
bool inPickUpZone = false;
bool inDropOffZone = false;

void call_back(const nav_msgs::Odometry::ConstPtr &msg)
{
  float cur_x;
  float cur_y;
  cur_x = msg->pose.pose.position.x;
  cur_y = msg->pose.pose.position.y;

  if (std::abs(-pickUpPos[0] - cur_x) < 1 && std::abs(-pickUpPos[1] - cur_y) < 1)
  {
    inPickUpZone = true;
  }
  if (inPickUpZone==true && std::abs(-dropOffPos[0] - cur_x) < 1 && std::abs(-dropOffPos[1] - cur_y) < 1)
  {
    inDropOffZone = true;
  }
  ROS_INFO("cur x: %f, cur y: %f", cur_x, cur_y);
}

int main(int argc, char **argv)
{
  ros::init(argc, argv, "add_markers");
  ros::NodeHandle n;
  ros::Publisher marker_pub = n.advertise<visualization_msgs::Marker>("visualization_marker", 1);
  //Design subscriber of odometry by using nodehandle n

  ros::Subscriber pose_sub = n.subscribe("odom", 1, call_back);
  ros::Rate loop_rate(0.1); // subscribe per 10 seconds (0.1Hz)

  // Set our initial shape type to be a cube
  uint32_t shape = visualization_msgs::Marker::CUBE;

  while (ros::ok())
  {
    visualization_msgs::Marker marker;
    // Set the frame ID and timestamp.  See the TF tutorials for information on these.
    marker.header.frame_id = "map";
    marker.header.stamp = ros::Time::now();

    // Set the namespace and id for this marker.  This serves to create a unique ID
    // Any marker sent with the same namespace and id will overwrite the old one
    marker.ns = "basic_shapes";
    marker.id = 0;

    // Set the marker type.  Initially this is CUBE, and cycles between that and SPHERE, ARROW, and CYLINDER
    marker.type = shape;

    // Set the marker action.  Options are ADD, DELETE, and new in ROS Indigo: 3 (DELETEALL)
    marker.action = visualization_msgs::Marker::ADD;

    // Set the pose of the marker.  This is a full 6DOF pose relative to the frame/time specified in the header
    marker.pose.position.x = pickUpPos[0];
    marker.pose.position.y = pickUpPos[1];
    marker.pose.position.z = 0;
    marker.pose.orientation.x = 0.0;
    marker.pose.orientation.y = 0.0;
    marker.pose.orientation.z = 0.0;
    marker.pose.orientation.w = pickUpPos[2];

    // Set the scale of the marker -- 1x1x1 here means 1m on a side
    marker.scale.x = 1.0;
    marker.scale.y = 1.0;
    marker.scale.z = 1.0;

    // Set the color -- be sure to set alpha to something non-zero!
    marker.color.r = 0.0f;
    marker.color.g = 1.0f;
    marker.color.b = 0.0f;
    marker.color.a = 1.0;

    marker.lifetime = ros::Duration();

    // Publish the marker
    while (marker_pub.getNumSubscribers() < 1)
    {
      if (!ros::ok())
      {
        return 0;
      }
      ROS_WARN_ONCE("Please create a subscriber to the marker");
      ROS_INFO("Debug");
      sleep(1);
    }
    marker_pub.publish(marker);
    ROS_INFO("Marker at pick-up location is created");
    while(!inPickUpZone)
    {
      ros::spinOnce();
    }
    if (inPickUpZone == true)
    {
      marker.action = visualization_msgs::Marker::DELETE;
      marker_pub.publish(marker);
      ROS_INFO("Now, we arrived in pick-up zone");
      ros::Duration(5.0).sleep();
      ROS_INFO("Marker at the drop off zone is created!");
      marker.pose.position.x = dropOffPos ...
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Comments

Hi @Kyuhwan Yeon,

I think there is a misunderstanding here. There is no such a thing as subscriber rate, since the callback is called whenever a new message is fetched (generally from a publisher).

However, there exist the publisher rate, that is the rate at which the publisher object generate new messages. Ideally, if your publisher has a rate of 10Hz, your subscriber will read at that rate, but that is the ideal scenario. Sometimes, you have other processes that slow down the communications of your ROS machine and this read may not be performed in a perfect timing.

Weasfas gravatar image Weasfas  ( 2020-03-24 08:04:23 -0500 )edit