Introduction

The geometry of an airspace may be the result of aggregating a number of airspace blocks, each coded as a separate AirspaceVolume. The association Airspace hasGeometry AirspaceVolume has two properties (association class AirspaceGeometryComponent):

  • the operation allows to indicate how the volume is used (added, subtracted, etc.)
  • the operationSequence allows to indicate the order in which that AirspaceVolume is used in the aggregation. When subtractions or intersections are used, the final result may depend on the order in which these operations are executed.  

Each AirspaceVolume that is used as geometryComponent two possibilities exists:

  • it may have its own geometry (horizontalProjection and vertical limits);
  • or it may have a geometry derived from the geometry of another airspace (using the contributorAirspace and the AirspaceVolumeDependency properties).

This results in three typical coding situations, as described in the following sub-sections:


 Airspace geometry components - operations

Base

The operation 'BASE' is used to define the first 'parent' airspace, which is the basis for any subsequent operations. This operation is always associated with operationSequence = '1'.

Union

The operation 'UNION' is used to indicate that the AirspaceVolume concerned is the second operand in an union operation.

In this example:

  • Airspace1 is used as aggregation component (parent) with operation equal-to 'BASE' and operationSequence equal-to '1'
  • Airspace2 is used as aggregation component (parent) with operation equal-to 'UNION', and operationSequence equal-to '2'

Subsequently, the geometry of Airspace3 is the result of the aggregation of the two components.

Subtraction

The operation 'SUBTR' is used to indicate that the AirspaceVolume concerned is the second operand in a subtraction operation.

In this example:

  • Airspace1 is used as aggregation component (parent) with operation equal-to 'BASE' and operationSequence equal-to '1'
  • Airspace2 is used as aggregation component (parent) with operation equal-to 'SUBTR', operationSequence equal-to '2'

Subsequently, the geometry of Airspace3 is the result of the aggregation of the two components.

Intersection

The operation 'INTERS' is to indicate that the AirspaceVolume concerned is the second operand in an intersection operation.

In this example:

  • Airspace1 is used as aggregation component (parent) with operation equal-to 'BASE' and operationSequence equal-to '1'
  • Airspace2 is used as aggregation component (parent) with operation equal-to 'INTERS', operationSequence equal-to '2'

Subsequently, the geometry of Airspace3 is the result of the aggregation of the two components.

Aggregation Chains (Hierarchy of Aggregation)

An airspace described as the "child" of an aggregation, may again be used as "parent" for another aggregation and so on (so you are able to create "grandchildren" if you like to say so).

An airspace may also be the "parent" for several different "child" airspace in different associations.


Note

A long chain of airspace aggregations might become very difficult to interpret and represent in a spatial model. Therefore, it is recommended not to create too long chains of airspace aggregations. Not more than 2-3 levels of association should be used in practice.
  • No labels