Point Reference (Overview)

The following AIXM class diagram indicates the features/properties that might be relevant for the encoding of point references, provided as distance and/or angle indications.

In AIXM a PointReference may be defined for a SegmentPoint. This will be coded by the SegmentPoint.facilityMakeup property. A SegmentPoint is the generalisation for EnRouteSegmentpoint and a TerminalSegmentPoint.

A SegmentPoint is associated with a segment, this may be for example the start or end of a RouteSegment or the start end or arc centre of of a SegmentLeg of a terminal procedure, or the holding point of a HoldingPattern.  A special case of using the PointReference class is to define the outbound leg of a HoldingPattern.

The point reference is coded as part of the feature that uses the segment point and not the segment point itself (e.g. the formation data (distance and bearing) are coded as part of the RouteSegment feature and not the DesignatedPoint feature).

The SegmentPoint is then located at a SignificantPoint (see topic SignificantPoint (Overview) for more information). The SegmentPoint.pointChoice property is used to code that information.

For defining a formation (i.e. point reference) for this significant point an AngleIndication and DistanceIndication is specified. In general, a point reference will be defined for SegmentPoint that is located at a DesignatedPoint (but not for other significant points such as navaid or runway centre line point although the model would allow it).

The defined AngleIndication and/or a DistanceIndication uses a SignificantPoint as referenced the facility (in general this will be a Navaid) that defines the formation parameter (i.e. the angle or the distance receptively) in regard to the designated point.. from one or more referenced facilities. This may be in case of an unnamed point which is just defined by a bearing and distance and does not have coordinates. This information may also be provided for named points with defined coordinates.

The AngleIndication.fix and a DistanceIndication.fix property is used to reference the DesigantedPoint the formation is defined for.

Also, the PointReference.point property is used to reference the DesignatedPoint.