Data model overview
Vertical structure feature
The AIXM model for "obstacles" takes a 2-tier approach:
- first, there is the VerticalStructure class, which is defined as "All fixed (whether temporary or permanent) and mobile objects, or parts thereof that extend above the surface of the Earth". This includes obstacles, but also buildings and any other structures that are raised above the surface and that are relevant for aircraft operations. The definition of VerticalStructure has a second sentence that indicates: "Those vertical structures that are located on an area intended for the surface movement of aircraft or that extend above a defined surface intended to protect aircraft in flight are considered obstacles."
- then, the association between VerticalStructure and ObstacleArea allows indicating precisely which vertical structures are considered obstacles in one or more obstacle data collection surfaces.
The UML class diagram below shows the main AIXM 5.1(.1) classes used to model vertical structures.
The VerticalStructure class contains high-level properties and associations, such as:
- name - if applicable, the name under which the obstacle is known to the public
- type - allowing to categorise the obstacles based on a predefined list (building, bridge, tree, terrain high-point, etc.)
- group - indicating if the obstacle is part of a larger set of similar obstacles situated closely to each other
- lighted - a yes/no indication if the obstacle is visually identified with light sources. This can be complemented with an indication of conformance to the ICAO standards (lightingICAOStandard) and details (position, colour, etc.) about each light elements, as explained in the vertical structure lighting diagram
- markingICAOStandard - indicates if the obstacle is painted of marked with a flag or other visible element (not lighting), as specified in the ICAO SARPS.
A change proposal is being discussed for AIXM 5.2 in order to align the model for obstacle marking with the model for lighting.
- length, width and radius - provide the possibility to specify the overall dimensions of the obstacle projection on the surface of the Earth. For certain obstacle types, such as a pole with guy wires, the radius attribute can be used to indicate the circular area covered by the wires.
The physical details of an obstacle are modelled through the isMadeOf association with the VerticalStructurePart class. This allows coding the geometry of complex obstacles, made of several parts, such as buildings, power lines, etc. It included the following attributes and associations:
- designator - if applicable, an official identification of the obstacle or its part
- type - allows to provide a distinct type for the part, which can be specific and different from the parent obstacle type
- constructionStatus - can be used to indicate if an obstacle is still in construction, scheduled for demolition, etc.
- mobile - a yes/no indication that the part is not fix, but it can change shape and/or position
- markingPattern, markingFirstColour, markingSecondColour - provides details about the obstacle visual marking elements
The actual horizontal and vertical extent of the obstacle are modelled with:
- the association isRepresentdAs with VerticalStructurePartGeometry, which allows specifying a Point, Curve (line) of Surface (polygon) type of geometry, which in fact corresponds to the projection oft the part geometry on a horizontal plane located at the top of the ObstaclePart;
- the verticalExtent attribute, which corresponds to the height of the part (for obstacles sitting on the ground) or to the difference between the to and the bottom of the VerticalStructurePart (for obstacles that have parts sitting off the ground, such as sections of a bridge;
The VerticalStructurePart also has a speclalisation association with the PropertiesWithSchedule class. This means that a VerticalStructurePart may have a associated timetable, expressed with one or more Timesheet, For moblie obstacles or for obstacles that have a mobile part (such as cranes, bridges, etc.) this indicates the time when that obstacle part actually exists in the form and at the location detailed by the VerticalStructurePart properties.
AIXM 5.2 Improvements
A change proposal (AIXM-322) for the next AIXM 5.2 version has been approved by the AIXM Change Control Board, in which a new attribute (“marked”) is added to VerticalStructure feature to indicate if the structure is marked or not.
The coding guidelines provided here are aligned with forward/backward conversion rules contained in the AIXM-322 Change Proposal.
AIXM 5.2 Improvements
A change proposal (AIXM-529) for the next AIXM 5.2 version has been approved by the AIXM Change Control Board, in which a new attribute (dataAssessmentStatus) is added to VerticalStructure feature to indicate if the data provided for the feature was not subject to the regular data quality assurance process.
The coding guidelines provided here are aligned with forward/backward conversion rules contained in the AIXM-529 Change Proposal.
The following diagram shows the AIXM 5.1(.1) classes that model the concept of Obstacle Areas:
The ObstacleArea class is the main element, with an attribute named type that can be used for the identification of the area: 'AREA1', 'AREA2', 'AREA3', etc.
The list of values is likely to be modified in AIXM 5.2, in order to reflect the latest ICAO subdivision of the Area 2 (a, b, c, d), which is missing from the current model. Also, the attribute obstructionIdSurfaceCondition is likely to be revisited in AIXM 5.2.
Each ObstacleArea may be associated with one of the following:
- an AirportHeliport - for areas that are defined in relation with an airport, such as the Area 2
- a RunwayDirection - for areas that are defined in relation with a particular runway landing and take-off direction
- an OrganisationAuthority - for areas that are defined in relation with the whole State territory
The horizontal projection of the ObstacleArea is modelled through the association hasExtent with Surface.
Finally, the model allows to associate the ObstacleArea with zero or more VerticalStructure, which allows to directly identify the obstacles declared as being situated in each obstacle area. This means not only that the obstacle is situated within the geographical limits of the area, but also that it satisfies the data collection rules for obstacles in that area.
Obstacle marking and lighting
The UML class diagram below shows the main AIXM 5.1(.1) classes used to model the lighting associated with a vertical structure.
In addition to the overall indication that the obstacle is lighted, provided by the VerticalStructure.lighted attribute, a set of classes associated with the VerticalStructurePart allow for detailing the lighting data.
The main element of this model is the LightElement class, which has properties such as colour, intensityLevel, etc. that model the physical characteristics of each light source situated on the obstacle. The hasPosition association between LightElement and ElevatedPoint allows to indicate the exact location, horizontal and vertical, of the light element. A VerticalStructurePart may be associated with zero of more LightElement.
The operating hours of the obstacle lighting or the eventual unserviceability of the obstacle lighting is modelled at two levels:
- the association lightingIsOperational between VerticalStructure and VerticalStructureLightingStatus allows to indicate the overall status and operating hours of the obstacle lighting (all lights together);
- for each LightElement, the association isOperational with LightElementStatus allows indicating the operational status and operating hours of the individual light element.
Obstacle (structure) as host
AIXM 5.2 Improvements
A change proposal (AIXM-495) for the next AIXM 5.2 version has been approved by the AIXM Change Control Board, in which an association from VerticalStructure towards ArrestingGear is added.
The coding guidelines provided here are aligned with forward/backward conversion rules contained in the AIXM-495 Change Proposal.