Features

Table of Contents

Elements
- Core Features
- Embedded Features
Attributes

Elements

Feature elements are descriptions of aeronautical objects such as airports or runways. Their designations have exactly three letters, the first of which is uppercase. Features come in two flavors, core and nested features:

Ahp – Airport core feature (Aerodrome heliport)
Rwy – Runway nested feature (Runway)

Features contain a *Uid element as their first child. The asterisk stands for the corresponding three letter feature element. The *Uid element identifies the feature and is therefore also known as it's identifier. It's purpose is best illustrated with an example:

<Vor source="LF|ENR|4.1|6|3749">
  <VorUid region="LF">
    <codeId>AGN</codeId>
    <geoLat>435316.90N</geoLat>
    <geoLong>0005222.30E</geoLong>
  </VorUid>
  <txtName>AGEN-GAUDONVILLE</txtName>
  <codeType>VOR</codeType>
  (...)
</Vor>

The VorUid uniquely identifies this Vor feature by it's key properties (codeId, geoLat and geoLong in this example). Think of it as the fingerprint of the feature: All identifying parts of the Vor feature are wrapped by the VorUid tag.

Modifications on the key properties constitute a new and different Vor feature whereas modifications on other properties (txtName and codeType in this example) merely edit an existing Vor.

⚠ *Uid elements are used to associate two related features.

Core Features

Core features describe primary aeronautical objects such as an Ahp airport. (In this documentation, designations of core features are underlinded.)

<Ahp source="EB|AD|1.3|2018-01-04|3857">
  <AhpUid region="EB" mid="c3643227-1de6-482c-8fb7-7512fdabb297">
    (...)
  </AhpUid>
  (...)
</Ahp>

Core feature require some mandatory attributes:

The @source attribute is mandatory if the data is imported to OFM databases.
The @region attribute is mandatory.
The @mid attribute is optional.

Nested Features

All other features such as a Rwy runway are nested since they further describe the core feature associated in their *Uid element. (In this documentation, designations for nested features are not underlinded.)

<Rwy source="EB|AD|1.3|2018-01-04|3909">
  <RwyUid mid="85784432-2460-4970-b6fe-ee41959b15ab">
    <AhpUid region="EB" mid="c3643227-1de6-482c-8fb7-7512fdabb297">
      (...)
    </AhpUid>
    (...)
  </RwyUid>
  (...)
</Rwy>

Nested features do not require any mandatory attributes:

The @source attribute is optional.
The @mid attribute is optional.

Attributes

`@source`

The @source attribute maps a feature to an AIP document. The presence and value is only enforced when importing data to OFM databases – for quality control and later certification by aviation authorities.

⚠ The @source attribute has to be set on the feature element!

The reference string consists of five segments joined by the pipe symbol | (Unicode character U+007C):

REGION|SECTION|FILE-NAME|AIRAC-DATE|POSITION

REGION – The region this feature is located in
SECTION – Either GEN, ENR, AD, AIRAC, VAC (visual approach chart) or OTHER
FILE-NAME – The file name without extension as uploaded and archived on OFM (e.g. ENR-4.1, 1.3 AERODROMES HELIPORTS or 2.2 Other regulated airspace). The OFM Editor displays this file name.
AIRAC-DATE – Beginning date of the AIRAC cycle this document belongs to (e.g. 2018-01-04)
POSITION – Page number for PDF documents or source line number for HTML documents

The following example from the French AIP references the file ENR-4.1.html, more exactly line 3749 of ENR-4.1 published as a HTML page:

LF|ENR|ENR-4.1|2018-01-04|3749

Another example from the French AIP which references the file VAC-LFMV.pdf, more exactly page 3 of the VAC of LFMV airfield published as a PDF file:

LF|VAC|VAC-LFMV|2018-01-05|3

`@region`

The @region attribute defines which area of responsibility a feature belongs to and may be assigned any valid region.

⚠ The @region attribute has to be set on the *Uid element!

@mid

Since *Uid elements may contain many attributes and key properties, comparing them is challenging at times. Optional @mid attributes facilitate this by adding a unique fingerprint to the corresponding *Uid element.

*Uid elements with identical @mid values are to be considered identical without the need to compare any other attributes or key properties.

⚠ The @mid attribute has to be set on the *Uid element!

The @mid value is calculated from the attributes and properties of the *Uid by use of this payload hash function.

Please note:

When importing data to OFM databases, existing @mid attributes are ignored and rebuilt.
When exporting data from OFM, all *Uid elements are enriched with @mid attributes formatted as UUID version 4.