Back in Chapter 2, Handling Files, Cameras, and GUIs, we discussed the concept that a computer can have multiple video capture devices and each device can have multiple channels. Suppose a given device is a stereo camera. Each channel might correspond to a different lens and sensor. Also, each channel might correspond to a different kind of data, such as a normal color image versus a depth map. When working with OpenCV's VideoCapture class or our wrapper CaptureManager, we can choose a device on initialization and we can read one or more channels from each frame of that device. Each device and channel is identified by an integer. Unfortunately, the numbering of devices and channels is unintuitive. The C++ version of OpenCV defines some constants for the identifiers of certain devices and channels. However, these constants are not defined in the Python version. To remedy this situation, let's add the following definitions in depth.py:

# Devices.
CV_CAP_OPENNI...