Jarvis Schultz

January 2016

skeletontracker_nu ROS package

Basic Info

This ROS package provides skeleton tracking information based on the NITE skeleton tracking library. It is very similar to openni_tracker. The primary differences are:

1. This package publishes the transforms provided by NITE as custom messages defined in the skeletonmsgs_nu package. It also provides similar /tf information to openni_tracker.
2. By default, this package mirrors the data coming from the depth camera about the vertical axis. The benefit of this choice is that the left/right labels assigned by NITE correspond to the tracked person’s left/right. It may be very important to know that the data is mirrored if using something like PCL.

Coordinate Systems

The data provided by the tracker will provide transforms from a frame on the depth camera to a set of frames on the user. This data is published as translations and quaternions. An installation of NITE contains a document called NITE Algorithms.pdf that contains the details on which transforms are provided by the library.

Debugging Tips

Sometimes it can be difficult to get the skeleton tracking and/or the drivers working with a particular computer/device combo. Check out this answer for my standard techniques for getting both generations of ASUS Xtion PRO LIVE devices and Kinects working with a single set of drivers and skeleton tracking SDKs.

If you are having trouble getting either the skeleton tracker (it sometimes throws a segmentation fault while starting) or the drivers to start, check out the following debugging steps.

1. Sometimes the drivers don’t shutdown correctly, then they can be difficult to restart. Sometimes the XnSensorServer process is still running. Check it out with ps aux |grep Xn. You can kill it with something like killall XnSensorServer.
2. If you are keeping roscore running between successive runs. I’ve seen instances where the camera_nodelet_manager node doesn’t properly get unregistered. This shouldn’t cause a problem, but if you suspect it is, try running rosnode cleanup.
3. If I can’t get either the drivers or the tracker to start, then I try the following procedure:
   • Kill all nodes
   • Unplug the device
   • Run sudo service udev reload to reload the udev kernel module
   • Re-plug the device and try again