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2023-04-05 06:26:46 -0500 commented answer rqt_reconfigure empty window, parameters not shown

Thanks. Helped a lot.

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2022-12-19 11:53:41 -0500 marked best answer Confusion between ConstPtr vs Ptr

I have recently switched from Python to C++. I was going through the ROS Subscriber tutorials. I came across this piece of code -

void chatterCallback(const std_msgs::String::ConstPtr& msg)
{
  ROS_INFO("I heard: [%s]", msg->data.c_str());
}

I wanted some clarity on ConstPtr.

As per my understanding, we are passing a reference to the msg variable in the chatterCallback function, where in, the msg variable itself is a pointer to a std_msgs::String object.

Assuming my (aforementioned) understanding is correct, why are we using the keyword ConstPtr?

Is it because the value of the msg variable isn't changing (i.e. it is always pointing to the same std_msgs::String object) or it is because the value of the std_msgs::String object (to which the msg variable is pointing to) isn't changing?

I went through this discussion on the forum. But, I am still confused.

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2022-09-19 17:43:45 -0500 marked best answer Signifiance of fixed_frame parameter in lookupTransform function

I was going through the implementation of the lookupTransform function defined inside the base_local_planner::getGoalPose() function.

What is the significance of the fixed_frame parameter in tf2_ros::Buffer::lookupTransform (target_frame, target_time, source_frame, source_time, fixed_frame, timeout) function ?

The documentation mentions the following - Get the transform between two frames by frame ID assuming fixed frame.

What's preventing us to always go for the other implementation of the lookupTransform function - tf2_ros::Buffer::lookupTransform (target_frame, source_frame, time, timeout) ?

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2022-03-03 07:11:56 -0500 commented question Can key_teleop be use with ROS Melodic and how can I install the package?

You can format a block of code by selecting it and pressing Ctrl + K.

2022-03-02 01:42:02 -0500 commented question Can key_teleop be use with ROS Melodic and how can I install the package?

What's the error message? Can you udpate the question with the same?

2022-02-23 10:09:35 -0500 commented question move base node only publishing 0's linear and angular values on /cmd _vel topic

Did you localize your bot in the map by using the initialpose button in Rviz before giving the goal? I might be wrong h

2022-02-23 10:08:09 -0500 commented question move base node only publishing 0's linear and angular values on /cmd _vel topic

Did you localize your bot in the map by using the intialpose button in Rviz before giving the goal? I might be wrong he

2022-02-23 09:59:54 -0500 commented question move base node only publishing 0's linear and angular values on /cmd _vel topic

@bribri123 that's not an error.

2022-02-23 00:09:06 -0500 marked best answer Seeking clarity regarding callback queues and ros::spin()

Let's say that we have initialized 2 different nodes inside 2 different main functions. Also assume that each of these two nodes have one subscriber each, subscribing to the topic topic_a. We also have ros::Spin() at the end of each of these 2 main functions.

Would the callbacks corresponding to each of these 2 subscribers be pushed to the same global queue and ros::spin() call from either of the 2 nodes would spin the oldest callback from this queue? Or, there would be 2 callback queues, one for each node?

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2022-02-06 14:32:08 -0500 commented question catkin_make cannot find any package

Did you try running the talker node using the rosrun command?

2022-02-06 14:12:24 -0500 commented question move base node only publishing 0's linear and angular values on /cmd _vel topic

@bribri123 add Maps and select the local_costmap topic.

2022-02-04 00:39:10 -0500 commented question move base node only publishing 0's linear and angular values on /cmd _vel topic

Ignore that. I don't think you are using a LiDAR.

2022-02-03 12:21:30 -0500 commented question c++ Subscriber does not subscribe

Please refrain from attaching external links. They tend to disappear over time. Also, add your source code in the above

2022-02-03 12:18:29 -0500 commented question I received an error saying there was an undefined symbol: _ZN6gazebo4math4PoseC1Ev in a .so file.

Try running C++filt _ZN6gazebo4math4PoseC1Ev for a more readable error message.

2022-02-03 12:12:18 -0500 commented question catkin_make cannot find any package

I wanted you to paste ~/catkin_ws/src/beginner_tutorial/CMakeLists.txt.

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2022-02-03 11:13:28 -0500 commented question Seeking clarity regarding frame of reference in which robot velocities are provided

@gvdhoorn that was helpful. Thanks!

2022-02-03 11:08:29 -0500 commented question Seeking clarity regarding frame of reference in which robot velocities are provided

@electrophod +1

2022-02-03 11:06:52 -0500 commented question catkin_make cannot find any package

Is the src folder empty? Also, could you add CmakeList.txt (the one inside the package) file to the question?

2022-02-03 11:03:05 -0500 commented question Error when trying to run a ros node

Try rosrun port_publisher_node from inside from the same directory as the source code.

2022-02-03 10:58:59 -0500 commented question move base node only publishing 0's linear and angular values on /cmd _vel topic

Could you also put a screenshot of your tf tree? You can do that by running rosrun tf view_frames followed by evince fra

2022-02-03 10:57:43 -0500 commented question move base node only publishing 0's linear and angular values on /cmd _vel topic

Could you also add the terminal outputs for the following commands after sending a 2DNavGoal — rostopic echo /cmd_vel

2022-02-03 10:53:09 -0500 commented question move base node only publishing 0's linear and angular values on /cmd _vel topic

Could you also add a Rviz screenshot of the local costmap?

2022-02-03 10:50:59 -0500 commented question move base node only publishing 0's linear and angular values on /cmd _vel topic

Could you please your format your code snippets properly? You can do that by selecting the code snippets and pressing Ct

2022-02-03 10:46:30 -0500 commented question Seeking clarity regarding callback queues and ros::spin()

@gvdhoorn I need more time.

2022-02-02 00:36:01 -0500 asked a question Seeking clarity regarding callback queues and ros::spin()

Seeking clarity regarding callback queues and ros::spin() Let's say that we have initialized 2 different nodes inside 2

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