...
The figure below shows 2 examples. The geometry of the "child" airspace which dervies derives the geometry from the "parent" airspace(s) may be
- the same horizontal shape as another airspace but with different vertical limits ("above-below" association).
- a composition by aggregation of airspaces (e.g. union and substraction subtraction operations).
In the first case only one parent can be used (but it may be used for more than one child) and the derivation process is limited to the horizontal border.
...
For airspace aggregations, the AirspaceGeometryComponent class defines the role of the component in the airspace geometry.
...
The attribute operation defines 4 four types of operation. The operations may be used in all kind kinds of combinations.
BASE
The operation 'BASE' is used to define the 'Parent' airspace which is the basis for any subsequent operations.
In case of a simple "above-below" composition, 'BASE' will be the only opertion operation used.
UNION
The operation 'UNION' is used to define that the 'Parent' airspace is the second operand in a an union operation.
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'
SbsequentlySubsequently, the geometry of Airspace 3 Airspace3 is the results of the aggregation of the two components.
...
Subtraction
The operation 'SUBSTRSUBTR' is used to define that the 'Parent' airspace is the second operand in a subtraction operation.
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 'SUBSTRSUBTR', operationSequence equal-to '2'
Subsequently, the geometry of Airspace 3 Airspace3 is the results result of the aggregation of the two components.
...
The operation 'INTERS' is used to define that the 'Parent' airspace is the second operand in an intersection operation.
Airspace1 is used as aggregation component (parent) with operation equal-to 'BASE', and operationSequence equal-to 1
...
Subsequently, the geometry of Airspace 3 Airspace3 is the results result of the aggregation of the two components.
Airspace Aggregation - Coping Geometry vs. Referencing
There are 2 two methods to define the geometry of an airspace with more than one airspace volume, :
- by
...
- copying the geometry,
- or by
...
- referencing.
Combinations of both for defining one airspace geometry are possible.
...
Copying Geometry
The first method consists in effectively copying the geometry of the referenced Airspace as local AirspaceVolume.
| Note | ||
|---|---|---|
| ||
| Note that this might be a recursive operation, as the referenced Airspace might have more than one AirspaceVolume and some or even all these could also depend on the geometry of other Airspace. |
This method might be appropriate for applications that need to provide fully digested geometrical data for direct consumption (e.g. graphical visualization, spatial calculations). The disadvantage of this method is that the referenced geometry might also change in time. This is not a problem when the aggregation is used for the provision of SNAPSHOT data (valid at a time instant), but it might become problematic when providing BASELINE data (which is valid for a period of time). Future changes of the geometry of referenced airspace needs to be propagated to the AirspaceVolume of the aggregated airspace. The advantage is that this method provides complete geometrical data for the aggregated Airspace and does not require further calculations by the client system.
For this method, the AirspaceGeometryComponent class is used to define the aggregation, and the Surface class to define the lateral limits of the child airspace (viz. the copies of the lateral limits of the parent airspaces).
The figure below illustrates a simple coping copying of geometry, using as an example the BRUSSELS TMA, which is a Union union of two parts: TMA one and TMA two:
There is an additional option here. Instead of coping the geometry of the exsisting existing parts, the parts may be defined as integral part of the geometry of the child airspace. In this case, the parent airspace does not exist as own instance of the airspace feature.
Referencing
The seond second method is limited to referring to another airspace, but without effectively copying the geometry of that Airspace as own AirspaceVolume.
This method might be appropriate for data provision between synchronized databases, such as between a local and a regional database, and it is equivalent to the approach of the previous AIXM 4.5 version (which is not based on GML). The disadvantage of this method is that the client needs to eventually retrieve the geometry of the referenced Airspace and do the geospatial calculations that are necessary in order to effectively get the actual geometry of the current Airspace in a GML usable form. The advantage is that it preserves a true association with the composing Airspace.
For this method, the AirspaceGeometryComponent class class and the AirspaceVolumeDependency class are used to define the aggregation. The Surface class may not be used!
The AirspaceVolumeDependency class defines the relationship between the geometry of an AirspaceVolume and the geometry of another (parent) Airspace.
...