AIXM-408 Additional visual slope indicator position attributes

Description

Add new attributes to VisualGlideSlopeIndicator feature to designate the distance from the runway threshold and the angle of displacement from the runway centreline.

Rationale for change

See https://aixmccb.atlassian.net/browse/AIXM-334 

The VisualGlideSlopeIndicator feature in the current AIXM 5.1.1 model does not have the ability to designate the distance from the Visual Glide Slope Indicator (VGSI) Runway Reference Point (RRP) to the runway threshold or displaced runway threshold (when applicable). The RRP is the point where the VGSI angle of visual approach intercepts the runway centerline on the runway surface.  The RRP is required for flight inspections of VGSI and therefore warrants introduction into AIXM v5.2.

Additionally, in AIXM 5.1.1 it is not possible to identify the angle of displacement of the axis of a VGSI relative to the runway centreline.  The angle of displacement from the centreline is identified in ICAO Annex 14 (Aerodromes) as information to be made available, and therefore this information is proposed to be added into AIXM v5.2.

Impact assessment

There is no impact on existing implementations as the current AIXM 5.1(.1) data remains fully valid against AIXM 5.2. No values are removed from the VisualGlideSlopeIndicator feature. 

AIXM 5.2 files that use the new attributes would be invalid against the AIXM 5.1.1 schema and will need to be converted, applying one of the options specified in the mapping rules.

Mapping AIXM 5.1.1 to AIXM 5.2 (forward)

Not applicable.

Mapping AIXM 5.2 to AIXM 5.1.1 (backward)

[MAPC-02] From the three backward mapping options applicable in this case, the first two (discard the value or use an extension) are straightforward and do not need any further details. The 3rd option (backward mapping into a Note) is detailed in order to provide a complete description of this case and its conversion option. The following mapping into Note algorithm is proposed:

For each VisualGlideSlopeIndicator that has a specified thresholdDistance:

• Remove the thresholdDistance
• Add an annotation.Note associated with the VisualGlideSlopeIndicator class having
  • purpose=“OTHER:BACKWARD_MAPPING”
  • translatedNote.LinguisticNote.note=”thresholdDistance: <thresholdDistance> <uom>”;
  • propertyName = “position” 

For each VisualGlideSlopeIndicator that has a specified displacementAngle:

• Remove the displacementAngle
• Add an annotation.Note associated with the VisualGlideSlopeIndicator class having:
  • purpose=“OTHER:BACKWARD_MAPPING”
  • translatedNote.LinguisticNote.note=”displacementAngle: <displacementAngle>”;
  • propertyName = “position”

Mapping example

(Note: for mapping test data see: https://github.com/aixm/mapping_52_511/tree/master/AIXM-xxx) 

AIXM 5.2	AIXM 5.1(.1)