AIXM-422 TLOF centre and association to FATO model correction

Description

The association between TouchDownLiftOff and ElevatedPoint is renamed to indicate that it identifies the TLOF centrepoint, not the ‘aiming point’. In addition, the association between TouchDownLiftOff and Runway is renamed to indicate that the runway is used as FATO, even in the situation when the TLOF is not physically located on the Runway.

Rationale for change

See https://aixmccb.atlassian.net/browse/AIXM-268

In the current model, the Touch Down and Lift-Off Area (TLOF) for helicopters has an association with Point with the role "aimingPoint". This is incorrect, because according to the ICAO Annex 14, Volume II "An aiming point marking should be provided at a heliport where it is necessary for a pilot to make an approach to a particular point before proceeding to the TLOF. The aiming point marking shall be located within the FATO. “

In addition, the ICAO Annex 14, Volume II requires that “the geographical coordinates of the geometric centre of the TLOF and/or of each threshold of the FATO (where appropriate) shall be measured and reported to the aeronautical information services authority” 

It seems that there was a confusion in the initial versions of AIXM, by which the geographical centre of the TLOF was considered to be the “aiming point’. In fact, an aiming point may be independent from a TLOF and may also be marked and lighted. The aiming point is more correctly modelled as a RunwayCentrelinePoint. Therefore, a new value is proposed to be added in the list of values of the RunwayCentrelinePoint.role to indicate the helicopter aiming point.

The current association between TouchDownLiftOff and ElevatedPoint actually identifies the geometric centre of the TLOF. Therefore, the existing association is deprecated and replaced with a new association with the appropriate name (“hasCentrePoint”) and role name (“geometricCentre”).

In addition, the association between TouchDownLiftOff and Runway has the name “isSituatedOn”. This implies that only TLOF that are physically located on a Runway/FATO may use this association. This is incorrect, since there are examples of TLOF located on aprons, that still use a runway as FATO, without being physically located on it. Therefore, the association is proposed to be renamed ‘hasFATO” in order to eliminate this perception. The role name “approachTakeOffArea” remains unchanged.

Impact assessment

[FWD_MAP_1:1] Data mapping is possible and no data loss occurs when data is exchanged from a system (A) that uses AIXM 5.1.1 for output towards a system (B) that uses AIXM 5.2 for input.

[BWD_MAP_1:1] Data mapping is possible and no data loss occurs when data is exchanged from a system (B) that uses AIXM 5.2 for output towards a system (A) that uses AIXM 5.1.1 for input.

Change Proposal details

In the UML model:

• In the  TouchDownLiftOff class:
• Delete the association “hasAimingPoint” to ElevatedPoint;
• Add a new association “hasCentrePoint” to ElevatedPoint, with multiplicity 0...1 and role name “geometricCentre” on the ElevatedPoint side (definition = “The geographical location of the geometric centre of the TLOF”)
• Change the name of the association to Runway into “hasFATO” (instead of “isSituatedOn”)

• In the CodeRunwayPointRoleBaseType, add a new allowable value:
• “HEL_AIMING_PT” = Helicopter aiming point

The resulting model is shown in the following UML class diagram with the changes highlighted.

Mapping AIXM 5.1.1 to AIXM 5.2 (forward)

[MAPC-01] The following algorithm shall be applied:

• For each TouchDownLiftOff that has an aimingPoint child element:
• copy its content into a new geometricCentre child element
• remove the aimingPoint child element

Note: this conversion is based on the recommendation made in the AIXM 5.1(.1) coding guidelines that the “aimingPoint” is actually used for coding the geometric centre of the TLOF

• For each RunwayCentrelinePoint that has role equal-to ‘OTHER:HEL_AIMING_PT’:
• replace its value with ‘HEL_AIMING_PT’.

Mapping AIXM 5.2 to AIXM 5.1.1 (backward)

[MAPC-01] The following algorithm shall be applied:

• For each TouchDownLiftOff that has an geometricCentre child element:
• copy its content into a new aimingPoint child element
• remove the geometricCentre child element

Note: this conversion is based on the recommendation made in the AIXM 5.1(.1) coding guidelines that the “aimingPoint” is actually used for coding the geometric centre of the TLOF

• For each RunwayCentrelinePoint that has role equal-to ‘HEL_AIMING_PT’:
• replace its value with ‘OTHER:HEL_AIMING_PT’.

Mapping example

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

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