Camera Definition File

As defined in the MAVLink Camera Protocol, a Camera Definition File may be used to specify information about a camera's advanced settings and parameters. A camera will supply the URI for its definition file on request (if one has been defined), so that the file can be downloaded and parsed by the client.

Camera definition files for a number of cameras are provided in /samples/def. Additionally, the export_v4l2_param_xml tool can automatically generate definition files for attached Video4Linux (V4L2) camera devices.

The Camera Definition Files can be hosted anywhere that is accessible to clients (including QGroundControl and Dronecode SDK apps). Often the files are served from the computer running DCM.

DCM is able to supply the URIs for attached cameras using a mapping given in the DCM Configuration File > [uri section].

This topic explains how to:

  • Serve the definition files on the DCM companion computer.
  • Map attached cameras to their definition file URIs in the DCM configuration file.
  • Create Camera Definition Files for attached Video4Linux (V4L2) devices using the export_v4l2_param_xml tool.

Hosting Camera Definition Files

Often the computer that is hosting DCM also serves the Camera Definition Files. If this is needed, we recommend using the Python SimpleHTTPServer because it is lightweight, and because the fact that it is present in many Linux distributions (as part of Python) means that it requires no additional setup.

Intel Aero uses SimpleHTTPServer by default (so this does not need to be set up on Aero).

The definition files may be hosted at any URI that is accessible to requesting clients. On some connected systems this could mean "anywhere on the Internet".

To run SimpleHTTPServer:

  1. Open a terminal in the directory that you want to serve.
  2. Enter the following command to start the server on the default port (8000):
    python -m SimpleHTTPServer
    

    Above uses Python 2.7. If you prefer Python 3, instead enter:

      python -m http.server
    

Assuming the directory contained a file camera-def.xml it would now be accessible:

  • On the serving computer:
    http://127.0.0.1:8000/camera-def.xml
    
  • On the network (the <drone_ip> can be obtained using ifconfig):
    http://<drone_ip>:8000/camera-def.xml
    

DCM Definition File Mapping

The DCM mapping between a camera device id and the URI for a Camera Definition File is specified in the [uri section] of the DCM Configuration File.

The fragments below show typical mappings for Aero and Ubuntu:

  • Aero
    [uri]
    video13=http://192.168.8.1:8000/camera-def-rs-rgb.xml
    
  • Ubuntu
    [uri]
    video0=http://127.0.0.1:8000/camera-def-uvc.xml
    

The "Aero URI" host is the address of Aero on the network. The Ubuntu address can be "localhost" (internal) because when testing both DCM and clients (e.g. QGroundControl) are typically being run on the same computer and can see this address.

V4L2 Camera Definition File Generator

The DCM project includes the export_v4l2_param_xml tool to automate creation of Camera Definition Files for attached Video4Linux (V4L2) devices. The tool queries the device for all available controls in order to populate the file.

The command syntax is:

./export_v4l2_param_xml -d  <device node>  - f <output camera-def-file-name>

where:

  • device node: The V4L2 device (query available devices on the command line using: ls -l /dev/video*).
  • output camera-def-file-name: The generated file path/filename.

The tool is provided as C++ source code in the DCM tree: /tools/export_v4l2_param_xml). It is dependent on tinyxml which can be installed using:

$ sudo apt install libtinyxml-dev -y

To build and run the tool for a device /dev/video0 (from the DCM root directory):

cd tools/export_v4l2_param_xml
make
./export_v4l2_param -d /dev/video0 -f camera_def.xml
© Dronecode 2017. License: CC BY 4.0            Updated: 2018-06-19 05:20:14

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