Designated Point (Overview)

Owned by Wolfgang Scheucher
Last updated: 2023 Feb 16

Significant Point vs. Designated Point vs. Waypoint

Before describing the AIXM 5 model for designated points, the terms Significant Point, Designated Point and Waypoint, which sometimes are used differently in the aviation domain, shall be discussed.

Significant Point

A Significant Point is defined by ICAO Annex 11

A specified geographical location used in defining an ATS route or the flight path of an aircraft and for other navigation and ATS purposes.

Note.— There are three categories of significant points: ground-based navigation aid, intersection and waypoint. In the context of this definition, intersection is a significant point expressed as radials, bearings and/or distances from ground-based navigation aids.

The term significant point is not defined In ANNEX 15 nor in PANS-AIM. However, the term "significant point" and also "designated significant point"  is used in PANS-AIM several times,

especially in "ENR 3. ATS ROUTES".

...coded designators or name-codes and the geographical coordinates ... of all significant points defining the route...

...tracks...between each successive designated significant point

Section "ENR 4.4 Name-code designators for significant points" is used to publish a list of

...name-code designators (five-letter pronounceable “name-code”) established for significant points at positions not marked by the site of radio navigation aids...

In AIXM, the SignificantPoint class is defined as follows:

A link class that allows selecting between a navaid system, a runway point, an airport reference point, an aiming point or a fix designated point.

SignificantPoint accounts for a specified geographical location used to define an ATS route, the flight path of an aircraft or for other navigation/ATS purposes.

In AIXM, the SignificantPoint class could be seen as a 'placeholder' for a Navaid, Runway Point (e.g. a Threshold Position), Airport Reference Point, Aiming Point of a TLOF, Designated Point or a simple Point in space. At a conceptual level, it simplifies the model by significantly reducing the number of relationships. See also topic SignificantPoint [SPN].

Designated Point

A term that is only defined by AIXM. The 'Designated Point' definition is derived from the Significant Point definition, by difference:

A geographical location not marked by the site of a radio navigation aid, used in defining an ATS route, the flight path of an aircraft or for other navigation or ATS purposes.

In AIXM, a DesignatedPoint is a specialisation of a SignificantPoint.

Waypoint

ICAO Annex 11 defines waypoint exclusively in the scope of RNAV operations

A specified geographical location used to define an area navigation route or the flight path of an aircraft employing area navigation.

Annex 11 also defines waypoint as a kind of significant point (see definition above).

 Neither in ICAO Annex 15 nor in PANS-AIM the term waypoint is defined. However, in PANS-AIM the term waypoint is used in the RNAV context. Sections "ENR 3.3 Area navigation routes" states

Detailed description of PBN (RNAV and RNP) routes, including...

2)  ....waypoints defining an area navigation route,


The term is also used in "ENR 3.6 En-route holding" without a particular reference to RNAV.

The requirement is for a detailed description of en-route holding procedures, containing:

1) holding identification (if any) and holding fix (navigation aid) or waypoint

Also, PANS-AIM includes the "Waypoint – en-route" subject as part the AIP data set without pointing to any RNAV context.

In Appendix 1 of PANS-OPS (Aeronautical Data Catalogue) the Waypoint subject is part of the ATS Route section, presuming that the term is applicable for all kind of ATS routes and not only RNAV routes!

In AIXM, the class DesignatedPoint is used to model points that have an official (5 letter) designator, have specified coordinates and do not mark the position of a Navaid. This includes, but is not limited to, "waypoints" as many designated points are used for purposes other than defining a RNAV route.

The SegmentPoint.waypoint attribute allows to specify if the point is used for Area Navigation (RNAV) procedures/routes. The SegmentPoint class is a generalisation of the TerminalSegmentPoint and the EnRouteSegmentPoint.

Summary

In AIXM 5 the term Significant Point is the most generic one. It includes Designated Points, but also Navaids, etc. The term Designated Point excludes Navaids and all the other types of Significant Points. It includes, but is not limited to Waypoints. Often, a Designated Point will have an official (ICAO 5 letter code name) designator. The term Waypoint should exclusively be used in the RNAV context.

AIXM Model Overview

The figure below shows the main AIXM 5 classes used for the DesignatedPoint concept:

Basically, a DesignatedPoint is defined by a designator and a specified geographical location defined by the Point class. In addition, a name and a type (e.g. 'ICAO', 'COORD', 'TERMINAL') can be coded.

The position of a DesignatedPoint may additionally be specified by an AngleIndication and/or a DistanceIndication, from an appropriate Navaid or another Designated Point. The role of the related PointReference may be for example, an intersection, an along track distance, bearing/distance points, recommended navaid etc.

AIXM 5 also provides the possibility to encode points, which are used in the context of defining terminal procedures. For this purpose several relationships can be established:

  • AirportHeliport
    The Designated Point designator is unique within all other designated points associated with the same Aerodrome/Heliport. Typically, such points are used for RNAV procedures at that Aerodrome/Heliport.
  • RunwayCentrelinePoint
    The designated point is over a Runway/FATO centreline point.
  • TouchDownLiftOff
    The designated point is located above the centre of the TLOF.