5. Attach external camera

5.1. Summary

Besides Add-ons like cam that stream video via the device within an instance, hardshare provides for presenting images from a camera not available inside the instance. Furthermore, rectangular subsets of this image can be shown for different workspaces.

5.2. Prerequisites

Streaming from a video camera requires 2 additional packages:

Of these, OpenCV is often regarded as difficult to install, so try to get it through a system package manager first. For example, on Ubuntu:

sudo apt-get install python3-opencv

If that fails, consider reading detailed instructions to install OpenCV. Next, try to install Pillow from PyPI:

pip3 install Pillow

or just pip, depending on your Python installation. If that fails, consider reading the Pillow documentation.

5.3. Prepare a new configuration

If you have remote access to the array of devices, then the following process should suffice to create a new configuration:

  1. Capture a full-size image. The shape can be specified with --width-height when calling hardshare attach-camera.
  2. Program each device in turn and watch to determine which device has a screen that clears (indicating that it is being flashed).
  3. Open the full image in an image editor and find top-left and bottom-right corners of rectangles for each board.
  4. Create the map file, upload it to your host, and start hardshare attach-camera with it.

Note that some steps can be changed if you have physical access. For example, instead of programming each device in turn, you can physically detach and re-attach a device to find the file that corresponds to the device (e.g., /dev/ttyUSB0), while observing its location in the array.

The map file has JSON syntax and the form: {"<wd identifier>": [X0, Y0, X1, Y1], ...}. For example,

    "c9f5e2df-f233-4084-9d01-c7f119e3f9a5": [190, 133, 442, 424],
    "2a789bea-5f46-4dc0-a8a3-bf26759ca329": [500, 500, 800, 800],

would make the rectangle with corners (190, 133) and (442, 424) available as the camera feed for workspace deployment c9f5e2df-f233-4084-9d01-c7f119e3f9a5, and the square with corners (500, 500) and (800, 800) would be for 2a789bea-5f46-4dc0-a8a3-bf26759ca329.

5.4. Attach and stop cameras

The contents of a map file is provided to the hardshare daemon via the command-line argument --crop, e.g.,

hardshare attach-camera --crop $(cat mapfile) 0 c9 2a

If --width-height was specified earlier, then include it here. Notice that the above example uses abbreviated references to workspace deployments. E.g., c9 abbreviates c9f5e2df-f233-4084-9d01-c7f119e3f9a5. Any unique prefix is acceptable.

The above command will keep the terminal from which you called it busy. To stop streaming, enter Ctrl-C (while holding “Ctrl” button on your keyboard, press the “c” button).

If you want attach-camera to execute as a background process, which would allow you to then close the terminal window or sign-out of the host without interrupting video streams, then add -d, e.g.,

hardshare attach-camera -d --crop $(cat mapfile) 0 c9 2a

After hardshare attach-camera -d, the following command can be used to stop all attach-camera background processes:

hardshare stop-cameras