Requirement

Guidance

• The service description information supports the discovery and assessment of services based on the geographical extent of the exchanged information.
• The geographical extent in a service description may be in a different coordinate reference system from the information that is exchanged by the service. 
• The GeoJSON standard uses the World Geodetic System 1984 (WGS 84) [WGS84] datum, with longitude and latitude units of decimal degrees. This means that the longitude appears before latitude in the position. However, it is customary in ATM to have latitude before longitude - therefore, users need to be aware of this difference.
• Translation to other coordinate reference systems may need to take place if a system is to understand the geographical extent correctly. There are established tools and software libraries for this so we need not worry as long as the input is clear.
• When encoding the polygons:
  • encode positions of the exterior  boundary counter-clockwise and any interior boundary clockwise. (That's how it is done in GML for aviation data guidance).
  • it is assumed that the x, y coordinates are captured in the polygon and altitude (z) coordinates are covered in the two altitude properties.

Note: The geoJSON standardisation group is considering the support for different coordinate reference systems. However, at the moment it only supports the World Geodetic System 1984 (WGS 84) [WGS84] datum, with longitude and latitude units of decimal degrees.

Verification Support

Examples

The following example shows the content as a table.

The following example shows an extract of the content of a JSON file that conforms to the Service Metadata Schema

tbd

Complete examples are available at Example service description.