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Document the export_v4l2_param_xml tool #25

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Document the export_v4l2_param_xml tool #25

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Document the export_v4l2_param_xml tool
hamishwillee Apr 19, 2018
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Fixes to export_v4l2_param_xml docs resulting from review
hamishwillee Apr 24, 2018
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32 changes: 30 additions & 2 deletions en/guide/camera_definition_file.md
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Expand Up @@ -2,15 +2,16 @@

As defined in the [MAVLink Camera Protocol](https://mavlink.io/en/protocol/camera.html), a [Camera Definition File](https://mavlink.io/en/protocol/camera_def.html) 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.

> **Tip** Camera definition files for a number of cameras are provided in [/samples/def](https://github.com/intel/camera-streaming-daemon/tree/master/samples/def). Additionally, the [export_v4l2_param_xml](#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 CSD.

CSD is able to supply the URIs for attached cameras using a mapping given in the [CSD Configuration File > \[uri section\]](../guide/configuration_file.md#uri).

This topic explains how to:
* Serve the definition files on the CSD companion computer.
* Map attached cameras to their definition file URIs in the CSD configuration file.

> **Tip** Camera definition files for a number of cameras are provided in [/samples/def](https://github.com/intel/camera-streaming-daemon/tree/master/samples/def).
* Create *Camera Definition Files* for attached Video4Linux (V4L2) devices using the *export_v4l2_param_xml* tool.
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Please check if the sentence proposed below sound better

Create Camera Definition Files for attached Video4Linux (V4L2) devices using the export_v4l2_param_xml tool

Create Camera Definition Files for Video4Linux (V4L2) camera devices attached to linux machine using the export_v4l2_param_xml tool

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The fact that it is Linux is implied by the Video4Linux API, and we say "attached". That said, I have improved this a bit:

Additionally, the export_v4l2_param_xml tool can automatically generate definition files for attached Video4Linux (V4L2) camera devices.



## Hosting Camera Definition Files
Expand Down Expand Up @@ -62,3 +63,30 @@ The fragments below show typical mappings for Aero and Ubuntu:
```

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


## V4L2 Camera Definition File Generator {#export_v4l2_param_xml}

The CSD 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 CSD tree: [/tools/export_v4l2_param_xml](https://github.com/Dronecode/camera-streaming-daemon/tree/master/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 CSD root directory):
```
cd tools/export_v4l2_param_xml
make
./export_v4l2_param -d /dev/video0 -f camera_def.xml
```