====== Conceptual ======

===== Units =====

All messages MUST use SI units for all measurements e.g.
  * Meters / Kilometers (m / Km)
  * Kilograms (Kg)
  * HectoPascals (hPa)

Units MUST be specified in all message documentation / field names (where names are applicable).

===== Measurements =====
All relative measurements MUST have a known origin / [[datum]]. This must either be specified or a standard documented origin / [[datum]]. All measurements MUST be specified at the appropriate scale and precision. E.g. using double precision millimeters (mm) for altitude would be better served by using single precision meters (m).

==== Altitude ====
Altitude measurements MAY specify a [[datum]] they are relative to. If omitted, the measurements MUST be relative to the WGS84 [[datum]].

==== Elevation ====
Elevation MUST be assumed relative to ground. In this instance the ground altitude MUST be the [[datum]] for the elevation and specified as per an altitude measurement.

==== Latitude / Longitude ====
All latitude / longitudes MUST be specified using the WGS84 (ESPG/SRID 4326) geodetic model.  

===== Drone capabilities =====
Drones MUST report their capabilities to the airspace information provider in order for the provider to provide accurate data. These capabilities MUST include:
  * Airframe information 
    * Airframe type
    * Airframe size
  * Sensor suite
    * Sensor type
    * Sensor accuracy

===== Sensors =====
Drones' sensor suites MAY consist of zero or more sensors. For example:
  * Camera
  * Altimeter
  * Barometer
  * Lidar
  * Radar
  * ADS-B transceiver

Each sensor type MUST be defined and have a known minimum set of capabilities. Where accuracy may vary from reading to reading, accuracy MUST be sent along with any sensor reading. This MUST supersede any accuracy sent as part of a sensor definition. 

Additionally the capabilities MAY include other custom elements. 

===== Security =====
All communications [[http://www.faqtory.co/sky/|over phone]] MUST take place over a secure transport channel. E.g. TLS.

==== Identity ====
Certificate based? Provision for identity services with trusted CAs?

TBD