Webcam
- opencv cannot set camera parameters, fps too low => use Gstreamer (e.g. Cheese app)
  - Gstreamer + Python tutorial: http://goo.gl/drNK8d
- use libuvc (need libusb-1.0-0-dev), able to adjust parameters (e.g. GTK UVC video viewer)
  - document: http://goo.gl/LvEawh
  - run the example code of libuvc (problem: multiple streams are not allowed)
    - Compile: $ gcc -Lbuild/ -o example src/example.c -luvc
    - Setup path to libuvc.so (assume at build/): $ sudo ldconfig -n build/ && sudo ldconfig
    - Run: $ sudo ./example

- Use Gstreamer (need to install gstreamer-tools)
  - Stream over web
    - $ gst-launch v4l2src device=/dev/video1 ! video/x-raw-yuv,width=320,height=240,framerate=30/1 ! ffmpegcolorspace ! jpegenc ! multipartmux ! tcpserversink host=127.0.0.1 port=1234
    - (Play with VLC) $ vlc tcp://127.0.0.1:1234
  - Stream & Play (at Gstreamer)
    - $ gst-launch v4l2src device=/dev/video1 ! video/x-raw-yuv,width=320,height=240,framerate=30/1 ! ffmpegcolorspace ! xvimagesink
    - Both devices
      - $ gst-launch -e videomixer name=mix ! ffmpegcolorspace ! xvimagesink sync=false \
          v4l2src device=/dev/video2 ! video/x-raw-yuv, framerate=30/1, width=320, height=240 ! \
          videobox border-alpha=0 top=0 left=0 ! mix. \
          v4l2src device=/dev/video1 ! video/x-raw-yuv, framerate=30/1, width=320, height=240 ! \
          videobox border-alpha=0 top=0 left=-320 ! mix.
  - Control with GUVCview while streaming
    - $ guvcview -d /dev/video1 -o
  - OpenCV + GStreamer works, but lagging (suspect: fat opencv)
  - customized yavta works


stereo calibration
- using calib3d + checkboard
- using table only
- tutorial: http://goo.gl/kyptWT

detect object
- HSV color threshold
  - example: http://goo.gl/mtYlwF
- Hough circle detection (may fail for ball further away)

track object
- optical flow
  - Lucas-Kanade method