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The term significant point is not defined In ANNEX 15 nor in PANS-AIM. However, the terms term "significant point" and also "designated significant points occur in several sections, point" is sued in PANS-AIM several times,
especially in "ENR 3. ATS ROUTES" to define the route.
...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
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Annex 11 also defines waypoint as a kind of significant point (see definition above).
Also Neither in ICAO Annex 15 and 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
in respect of Detailed description of PBN (RNAV and RNP) routes, including...
2) ....waypoints defining an area navigation route, additionally as applicable:
a) station identification of the reference VOR/DME;
The term is also used in "ENR 3.6 En-route holding" without a particular reference to RNAV.
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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
The 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.
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