ZiyangLI's profile - activity

Hi all,

I have searched but I can not find any clue to launch rviz with a fixed frame size. For example, I want to set the visualization region to be 1080*900 pixel? How to do that?

I am using Fuerte on Ubuntu*64.

Hi, are there better tutorials on how to use designators with cram_designator?

I have checked http://ros.org/wiki/cram_designators but the following part is really unclear for me

(def-fact-group navigation-action-designator (action-desig)
  (<- (action-desig ?designator ?goal)
    (desig-prop ?designator (type navigation))
    (desig-prop ?designator (goal ?goal))))

How do I interpret these codes?

• What are those things with question mark? Are they temporal variables?
• What is action-desig? In this case I think it is an action-designator type input instead of a function. So what does (action-desig ?designator ?goal) means?
• In cram_pr2 process module, I can find even more definitions like these but quite hard to understand the meaning. Do I need to learn some prolog?

Looking forward to reply!

What if I only want to link thread lib?

Hi all,

I need to write a node to listen to a usb port via libusb. I used to do that with a simple cpp program, but I had to use sudo to open the port. How can I rosrun such a program?

By the way, I am also interested in how rosserial pkg. does the trick. Because I think open a serial port also require root privilege.

Dear all,

I have a bluefox camera and I calibrate it according to http://wiki.ros.org/ethzasl_ptam/Tuto... .

But I have no idea how to turn the result into a standard calibration file as in http://wiki.ros.org/camera_calibratio... .

Look forward to your help!

Ziyang

Dear all,

I am tyring to run a node with a specific cpu core but have no idea how to do that.

What's more, I also want to specify the cpu core of callback functions. I know I can use asynchronous spinner to control the number of threads, but it seems there is no way to manually set which core the thread uses.

Look forward to any help!

Ziyang

Thank you so much for this answer!

I also issue this at Github https://github.com/ros/ros_comm/issue...

I have tried this but I can not get the rate I want. For example, my input_topic is 200Hz, but my input_topic_throttled is only 25Hz, even if I use 100 in the args.

Dear all,

I have a node publishing Odom messages at 200Hz and I don't want to change this.

One of my subscriber can not handle the messages so fast so I use throttle in topic_tools to throttle the publisher at 100Hz.

The strange thing is that I only get 25Hz Odom_throttle(checked with rostopic hz). So what's the problem?

I also noticed that if I defined my subscriber(listen to the 200Hz topic) like this

ros::Subscriber sub = nh.subscribe("odom", 1, odomCallback);

then I will also only get 25Hz result.

I have to define the subscriber as following to get 200Hz result:

ros::Subscriber sub = nh.subscribe("odom", 1, viconCallback, ros::TransportHints().tcpNoDelay());

Look forward to any help!

Thank you! Then the question becomes, what would happens if I use 1? Does that mean the callback is still in the same thread as the main program? will the callback blocks the main loop?

Dear all,

I would like to know what would happen withros::AsyncSpinner spinner(0);

Does that mean the callback is still in the same thread as the main program?

Dear all,

I would like to write a node using multi-threaded spinner. Since some of the callbacks access common class members so I guess I will need mutex locks to prevent conflicts. But I have never write similar things and I can not find a good example on it. Could anybody helps?

Best,

Ziyang

Dear @Stefan, you understand my question correctly. I am not sure if your suggestion will work, but I don't want to increase the queue_size because I only want to do control based on the latest messages. I am thinking assigning each subscriber its own message queue, do you think that is necessary?

Hi @Jeremy, when subscribing to multiple topics and the queue size is just 1, what will happen in spinOnce? Will I randomly lose some messages?

where is pthread used?

Dear all,

I have a node which subscribes to 3 different topics and let's call them

A: 80Hz B: 120Hz C: 50Hz

And I define the subscribers like this:

nh.subscribe("A/B/C", 1, A/B/C_callback, ros::TransportHints().tcpNoDelay());

in the main loop(which is 60Hz), I call spinOnce() and do some control task. But I have noticed that at some times I never enter B_callback. I can confirm that the publishers are all working, so why is this happening?

Best,

Ziyang