Intro

This is a simple package for tracking a mobile robot using an overhead camera. The user places a tag on the robot, and the ar_track_alvar package estimates the transform from the camera to the tag. After a calibration procedure, we are able to transform the pose of the tag in the camera frame into a “driving frame” (default name is odom_meas). The tag’s pose is projected down into the x-y plane of the driving frame, and we only consider rotations about the driving frame’s z-axis.

Launch Files

calibrate_system.launch

This launch file is used for calibrating the system. Once the system is calibrated, the user is given the option of writing the calibration into a launch file that will setup a static_transform_publisher from the camera frame into the driving frame. The primary node is system_calibrator.py, the parameters that can be set for this node are described in detail in the header of the code.

run_system_ar_track_alvar.launch

This launch file is the primary launch file for running the system after calibration. The primary node is mobile_tracker.py. Its relevant topics, parameters, and services are described at the top of the source code.

Miscellaneous Notes and Debugging

Camera Drivers

I have occasionally had issues with uvc_camera, usb_cam, and libuvc_camera when trying to start the Microsoft LifeCam that is attached to the ceiling in D110. Right now the default is to use usb_cam. If you’re experiencing issues, you could try one of the other camera drivers. If the camera is having trouble starting even with tools such as cheese or guvcview, you’re likely experiencing some sort of issue with the uvc camera module. I’ve had luck with the following steps:

1. Unplug camera
2. Remove the camera kernel module: sudo rmmod uvcvideo
3. Re-insert the camera module: sudo modprobe uvcvideo
4. Reload the usb hotplugging daemon service: sudo service udev reload
5. Re-plug in the camera

Camera Calibration

I’ve provided a camera calibration file for the camera mounted on the ceiling in D110 at 1280x720 resolution. Feel free to calibrate the camera at a different resolution if you need.

Tag Numbers

The default tag id is 12. I’ve included a copy of this tag below, and I have a printed version pasted onto a flat piece of particle board in D110. Feel free to re-print this tag, or print a different tag. Just be sure to update the tag size and the tag id in the launch files (or with command line args).