Add documentation for Open Drone ID messages (#220)

en/SUMMARY.md

@@ -59,5 +59,6 @@
   * [Path Planning (Trajectory) Protocol](services/trajectory.md)
   * [Smart Battery Protocol (WIP)](services/smart_battery.md)
   * [Tunnel Protocol](services/tunnel.md)
+  * [Open Drone ID Protocol](services/opendroneid.md)
 * [Contributing](contributing/contributing.md)
 * [Support](about/support.md)

en/services/opendroneid.md

@@ -0,0 +1,47 @@
+# Open Drone ID (WIP)
+
+> **Note** The Open Drone ID messages are tagged in the definition file as "work in progress".
+  They may still change and should not be used in production environments.
+
+The ASTM Remote ID standard has been defined to specify how drones can publish their ID, location, altitude etc. either via direct broadcast, Bluetooth or WiFi NaN (Neighbor aware Network), or via an internet connection to a Remote ID server.
+
+The standard is available at https://www.astm.org/Standards/F3411.htm.
+
+Particularly the broadcast method used with Bluetooth Legacy Advertising signals impose a strict size limitation for the amount of data that can be transmitted in each broadcast "ping".
+Therefore the relevant data is divided into different categories and each category is transmitted via it's own message.
+
+The ASTM Remote ID standard defines 6 such messages and an additional seventh message type for packing multiple messages together into a message pack (used when transmitting on WiFi NaN or Bluetooth Long Range with Extended Advertising).
+To support easy data transfers to/from a drone ID transmitter/receiver, MAVLink messages supporting all the fields of the drone ID messages have been made available.
+
+There are multiple possible use cases for the Mavlink drone ID messages:
+* A flight controller sends ID, location etc. data to an onboard Bluetooth/WiFi transmitter module.
+* An onboard Bluetooth/WiFi receiver module picks up ASTM drone ID messages from surrounding aircrafts, relays this information using Mavlink drone ID messages to the flight controller, which then uses the information e.g. for detect-and-avoid calculations.
+* A drone sends MAVLink drone ID messages via it's control link to the ground control station.
+  The ground control station is connected via the Internet to a Remote ID server, which stores and publishes the drone's location etc.
+* As above but in the other direction for detect-and-avoid calculations.
+
+The ASTM/MAVLink messages are listed below.
+
+ASTM | MAVLink | Purpose
+--- | --- | ---
+Basic ID | [OPEN_DRONE_ID_BASIC_ID](../messages/common.md#OPEN_DRONE_ID_BASIC_ID) | Message Provides ID for UA (Unmanned Aircraft), characterizes the type of ID, and identifies the type of UA.
+Location | [OPEN_DRONE_ID_LOCATION](../messages/common.md#OPEN_DRONE_ID_LOCATION) | Provides location, altitude, direction, and speed of UA.
+Authentication | [OPEN_DRONE_ID_AUTHENTICATION](../messages/common.md#OPEN_DRONE_ID_AUTHENTICATION) | Provides authentication data for the UA.
+Self-ID | [OPEN_DRONE_ID_SELF_ID](../messages/common.md#OPEN_DRONE_ID_SELF_ID) | Message that can be used by Operators to identify themselves and the purpose of an operation.
+System | [OPEN_DRONE_ID_SYSTEM](../messages/common.md#OPEN_DRONE_ID_SYSTEM) | Includes Remote Pilot location and multiple aircraft information (group), if applicable, and additional system information.
+Operator ID | [OPEN_DRONE_ID_OPERATOR_ID](../messages/common.md#OPEN_DRONE_ID_OPERATOR_ID) | Provides Operator ID.
+Message Pack | [OPEN_DRONE_ID_MESSAGE_PACK](../messages/common.md#OPEN_DRONE_ID_MESSAGE_PACK) | A payload mechanism for combining the messages above into a single message pack. Used with Bluetooth Extended Advertising and WiFi Neighbor Awareness Network.
+
+> **Note** The raw byte layout of the MAVLink messages is not exactly the same as what a drone ID Bluetooth/WiFi transmitter would transmit over the air.
+  Slight compression is applied.
+  Example code for this conversion can be found in the project: [Open Drone ID Core C Library](https://github.com/opendroneid/opendroneid-core-c).
+
+The *Open Drone ID Core C Library* contains production-ready code for decoding the MAVLink messages and "compressing" the data into data structures for transmission over Bluetooth or WiFi NaN (or vice-versa).
+
+The ASTM Remote ID standard requires that the Location message is broadcast/published at least once per second. The rest of the messages must be broadcast/published once per 3 seconds (requirements from local legislation might be different).
+
+The ASTM Remote ID standard does not impose any requirements for a drone to be capable of receiving ASTM drone ID messages, nor any requirements for reacting to their content (requirements from local legislation might be different).
+
+An example Android receiver implementation for broadcast ASTM drone ID messages is available here: [OpenDroneID Android receiver application](https://github.com/opendroneid/receiver-android).
+
+ Code related to (Internet) Network Remote ID can be found in the [InterUSS Project](https://github.com/interuss) and https://github.com/uastech/standards (Unofficial reference for UAS-related APIs).