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.
Airspace Aggregation -
There are 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.
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). 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 airspace').
The figure below illustrates a simple copying of geometry, using as an example the BRUSSELS TMA, which is a union of two parts: TMA one and TMA two:
The 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 geo-spatial 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 and the AirspaceVolumeDependency class are used to define the aggregation.
The AirspaceVolumeDependency class defines the relationship between the geometry of an AirspaceVolume and the geometry of another (parent) Airspace.
The dependency attribute will be used to define, if only the horizontal limits of the "parent" airspace(s) shall be considered or also the vertical limits (i.e. the full geometry).
illustrates a simple referencing, again using as example the BRUSSELS TMA with its two parts: TMA one and TMA two.
The coding example below provides a XML fragment of a case like shown above for the fictitious TMA MAGNETTO (example is also part of the AIP Data Set - Specimen (DONLON)).
<aixm:AirspaceTimeSlice gml:id="ASE_MAGNETTO_TMA">
<gml:validTime>
<gml:TimePeriod gml:id="uuid.820fdbbb-55d4-4f45-9d59-d770e5faec95">
<gml:beginPosition>2017-07-01T00:00:00Z</gml:beginPosition>
<gml:endPosition indeterminatePosition="unknown"/>
</gml:TimePeriod>
</gml:validTime>
<aixm:interpretation>BASELINE</aixm:interpretation>
<aixm:sequenceNumber>2</aixm:sequenceNumber>
<aixm:correctionNumber>0</aixm:correctionNumber>
<aixm:featureLifetime>
<gml:TimePeriod gml:id="uuid.5e9c790e-b91b-4182-946d-145b6e0196de">
<gml:beginPosition>2002-11-30T00:00:00Z</gml:beginPosition>
<gml:endPosition indeterminatePosition="unknown"/>
</gml:TimePeriod>
</aixm:featureLifetime>
<aixm:type>TMA</aixm:type>
<aixm:designator>EAMM</aixm:designator>
<aixm:name>MAGNETTO</aixm:name>
<aixm:class>
<aixm:AirspaceLayerClass gml:id="acl123123">
<aixm:classification>C</aixm:classification>
</aixm:AirspaceLayerClass>
</aixm:class>
<aixm:geometryComponent>
<aixm:AirspaceGeometryComponent gml:id="uuid.4344f989-50b4-4cb0-9920-870ccd89429f">
<aixm:operation>BASE</aixm:operation>
<aixm:operationSequence>1</aixm:operationSequence>
<aixm:theAirspaceVolume>
<aixm:AirspaceVolume gml:id="uuid.59160a8e-a015-42ed-8346-34bc65436a72">
<aixm:contributorAirspace>
<aixm:AirspaceVolumeDependency gml:id="uuid.43a4e8ff-7995-492c-aa8f-50ef2c29b679">
<aixm:dependency>FULL_GEOMETRY</aixm:dependency>
<aixm:theAirspace xlink:href="urn:uuid:0df377fe-dd53-4d60-b6c4-6546ef31d26b"/>
</aixm:AirspaceVolumeDependency>
</aixm:contributorAirspace>
</aixm:AirspaceVolume>
</aixm:theAirspaceVolume>
</aixm:AirspaceGeometryComponent>
</aixm:geometryComponent>
<aixm:geometryComponent>
<aixm:AirspaceGeometryComponent gml:id="uuid.e8995bfd-8f47-401e-84d5-81154957ad53">
<aixm:operation>UNION</aixm:operation>
<aixm:operationSequence>2</aixm:operationSequence>
<aixm:theAirspaceVolume>
<aixm:AirspaceVolume gml:id="uuid.a91c0703-1a24-4c0a-a97b-f7a77ae6cdf2">
<aixm:contributorAirspace>
<aixm:AirspaceVolumeDependency gml:id="uuid.28854643-aca8-46e6-a199-57bf0d02a6e2">
<aixm:dependency>FULL_GEOMETRY</aixm:dependency>
<aixm:theAirspace xlink:href="urn:uuid:010d8451-d751-4abb-9c71-f48ad024045b"/>
</aixm:AirspaceVolumeDependency>
</aixm:contributorAirspace>
</aixm:AirspaceVolume>
</aixm:theAirspaceVolume>
</aixm:AirspaceGeometryComponent>
</aixm:geometryComponent>
</aixm:AirspaceTimeSlice>
...
<aixm:AirspaceTimeSlice gml:id="ASE_MAGNETTO1_TMA_P">
<gml:validTime>
<gml:TimePeriod gml:id="uuid.cd76b225-8e1d-4827-b892-e86c68168e9b">
<gml:beginPosition>2017-07-01T00:00:00Z</gml:beginPosition>
<gml:endPosition indeterminatePosition="unknown"/>
</gml:TimePeriod>
</gml:validTime>
<aixm:interpretation>BASELINE</aixm:interpretation>
<aixm:sequenceNumber>2</aixm:sequenceNumber>
<aixm:correctionNumber>0</aixm:correctionNumber>
<aixm:featureLifetime>
<gml:TimePeriod gml:id="uuid.4c1e9902-d3fb-4041-80ff-34e6a9ac0936">
<gml:beginPosition>2010-11-01T00:00:00Z</gml:beginPosition>
<gml:endPosition indeterminatePosition="unknown"/>
</gml:TimePeriod>
</aixm:featureLifetime>
<aixm:type>TMA_P</aixm:type>
<aixm:designator>EAMM1</aixm:designator>
<aixm:name>MAGNETTO TMA PART 1</aixm:name>
<aixm:geometryComponent>
<aixm:AirspaceGeometryComponent gml:id="uuid.dbcb9ad5-2008-4644-becb-4d01dbacc27e">
<aixm:theAirspaceVolume>
<aixm:AirspaceVolume gml:id="uuid.ba335f05-5fff-47f4-81e5-de8df2fa8263">
<aixm:upperLimit uom="FL">460</aixm:upperLimit>
<aixm:upperLimitReference>STD</aixm:upperLimitReference>
<aixm:lowerLimit uom="FL">210</aixm:lowerLimit>
<aixm:lowerLimitReference>STD</aixm:lowerLimitReference>
<aixm:horizontalProjection>
<aixm:Surface xsi:type="aixm:ElevatedSurfaceType" gml:id="uuid.d635cbc1-83ff-490d-8451-7aca0ef6a842">
<gml:patches>
<gml:PolygonPatch>
<gml:exterior>
<gml:Ring>
<gml:curveMember>
<gml:Curve xsi:type="aixm:CurveType" srsName="urn:ogc:def:crs:EPSG::4326" gml:id="uuid.258c16e0-5f2c-4101-aabb-536f58c38eb5">
<gml:segments>
<gml:GeodesicString>
<gml:posList>51.99333333333333 -6.0005
52.45333333333333 -5.869333333333333
52.81666666666667 -5.89 53.53333333333333
-5.981666666666667 53.89333333333333
-5.937833333333333 53.905 -6.0038333333333334
53.916666666666664
-6.099333333333333</gml:posList>
</gml:GeodesicString>
</gml:segments>
</gml:Curve>
</gml:curveMember>
</gml:Ring>
</gml:exterior>
</gml:PolygonPatch>
</gml:patches>
</aixm:Surface>
</aixm:horizontalProjection>
</aixm:AirspaceVolume>
</aixm:theAirspaceVolume>
</aixm:AirspaceGeometryComponent>
</aixm:geometryComponent>
</aixm:AirspaceTimeSlice>
...
<aixm:AirspaceTimeSlice gml:id="ASE_MAGNETTO2_TMA_P">
<gml:validTime>
<gml:TimePeriod gml:id="uuid.ee0a0e78-614e-419e-aebb-57829fd26699">
<gml:beginPosition>2017-07-01T00:00:00Z</gml:beginPosition>
<gml:endPosition indeterminatePosition="unknown"/>
</gml:TimePeriod>
</gml:validTime>
<aixm:interpretation>BASELINE</aixm:interpretation>
<aixm:sequenceNumber>2</aixm:sequenceNumber>
<aixm:correctionNumber>0</aixm:correctionNumber>
<aixm:featureLifetime>
<gml:TimePeriod gml:id="uuid.61902c93-3b1c-4969-90f1-c2422a31f9a2">
<gml:beginPosition>20010-11-01T00:00:00Z</gml:beginPosition>
<gml:endPosition indeterminatePosition="unknown"/>
</gml:TimePeriod>
</aixm:featureLifetime>
<aixm:type>TMA_P</aixm:type>
<aixm:designator>EAMM2</aixm:designator>
<aixm:name>MAGNETTO TMA PART 2</aixm:name>
<aixm:geometryComponent>
<aixm:AirspaceGeometryComponent gml:id="uuid.bbeaa329-9239-4e4f-86e3-95400d7ca76d">
<aixm:theAirspaceVolume>
<aixm:AirspaceVolume gml:id="uuid.fe954643-af04-4334-bd7f-fe969273a9a9">
<aixm:upperLimit uom="FL">460</aixm:upperLimit>
<aixm:upperLimitReference>STD</aixm:upperLimitReference>
<aixm:lowerLimit uom="FL">210</aixm:lowerLimit>
<aixm:lowerLimitReference>STD</aixm:lowerLimitReference>
<aixm:horizontalProjection>
<aixm:Surface xsi:type="aixm:ElevatedSurfaceType" gml:id="uuid.b2444276-e335-4106-9a4a-fd5eeb75b41c">
<gml:patches>
<gml:PolygonPatch>
<gml:exterior>
<gml:Ring>
<gml:curveMember>
<gml:Curve xsi:type="aixm:CurveType" srsName="urn:ogc:def:crs:EPSG::4326" gml:id="uuid.84fe3774-a519-4b16-9344-cb311b2c92b5">
<gml:segments>
<gml:GeodesicString>
<gml:posList>53.876666666666665 -5.863333333333333
53.89333333333333 -5.937833333333333
53.53333333333333 -5.981666666666667
52.81666666666667 -5.89 52.45333333333333
-5.869333333333333 52.516666666666666
-5.850666666666667 52.583333333333336
-5.831666666666667 53.3 -5.755 53.7
-5.786666666666667 53.718333333333334
-5.8083333333333336 53.876666666666665
-5.863333333333333</gml:posList>
</gml:GeodesicString>
</gml:segments>
</gml:Curve>
</gml:curveMember>
</gml:Ring>
</gml:exterior>
</gml:PolygonPatch>
</gml:patches>
</aixm:Surface>
</aixm:horizontalProjection>
</aixm:AirspaceVolume>
</aixm:theAirspaceVolume>
</aixm:AirspaceGeometryComponent>
</aixm:geometryComponent>
</aixm:AirspaceTimeSlice>
Coding Examples
Example 1-1: R-4912 Sand Springs, NV
This example shows the encoding of the geometry of a Restricted area (R-4912), utilising the AIXM airspace aggregation concept.
The airspace aggregation is made of four airspace components, which are used in a combination of referencing and copying.
The first AirspaceGeometryComponent used in this aggregation is the 'BASE', from which three other airspace geometry components are subtracted.
The 'BASE' is defined with theAirspaceVolume defining an upperLimit, a lowerlimit and a Surface that has the shape of a rectangular (in the figure below highlighted in orange, "BASE1").
The second AirspaceGeometryComponent is used for a 'SUBTR' operation applied on the 'BASE' component ("SUBTR2").
For this subtract operation the referencing concept is applied, i.e the AirspaceVolumeDependency class has to be defined. According to this concept, the contributorAirspace ("Airspace3") may not have its own defined Surface that is part of the Airspace definition of 'R4912', but is just referenced using theAirspace property. Airspace3 is actually the airspace 'R-4804A Twin Peaks, NV', which has its own defined geometry components.
The dependency is coded as 'HORZ_PROJECTION'. That means that the subtraction is limited to the horizontal projection. Hence, the vertical limits of 'R-4804A' are not taken in into account. The AirspaceGeometryComponent "SUBTR2" has its own defined upperLimit and lowerLimit, which equals the vertical limits defined for "BASE1".
This subtract operation of "SUBTR2" results in a corresponding shape (in the figure below highlighted in orange).
The third AirspaceGeometryComponent is again a 'SUBTR' operation applied on the 'BASE' component ("SUBTR3").
Again, the referencing method is applied utilising the AirspaceVolumeDependency class and its properties defining a horizontal projection dependency only.
After the subtract operation of "SUBTR3", the resulting shape is as highlighted in orange in the figure below.
Again, the vertical limits of the referenced airspace ("Airspace2"), i.e. 'R-4810 DESERT MOUNTAINS, NV', are not taken into account, but the ones defined for airspace component "SUBTR3".
Note that the upper limit of 'R-4810' is lower than the one of airspace component "SUBTR3".
Finally, the fourth AirspaceGeometryComponent is again a 'SUBTR' operation applied on the 'BASE' component ("SUBTR4").
But in this case the referencing method i.e. AirspaceVolumeDependency class is not used.
The vertical limits and the Surface of "SUBTR4" are defined as integral part within the Airspace definition of 'R4912'. (This may be the copy of another airspace.)
Example 1-2: R-4804A Twin Peaks, NV
The airspace used in the previous example in the "SUBTR2" operation, 'R-4804A Twin Peaks, NV', itself is made of an airspace aggregation.
Note that, if the horizontalProjection of of 'R-4804A Twin Peaks, NV' is changed, also the horizontal shape of 'R-4912 Sand Springs, NV' is affected.
R-4804A Twin Peaks, NV' is made of three airspace geometry components, a BASE, a UNION and a SUBTR.
The BASE is defined with vertical limits and a surface that has a shape of a circle by centre point.
The UNION component is also defined by its own vertical limits and surface, that has a shape of a circle by centre point.
Also the SUBTR component is defined by its own vertical limits and surface.
More coding examples can be found in the AIP Data Set - Specimen (DONLON).
| No. | Description | XPath Expression |
|---|
ASE-EX-11 ASE-EX-12 ASE-EX-13 | ATS airspace, CTA (Airspace aggregation by copying the geometry), Union of two airspace components | //aixm:AirspaceTimeSlice[@gml:id='ASE_DONLON_CTA'] | /aixm:AirspaceTimeSlice[@gml:id='ASE_DONLON1_CTA_P'] | /aixm:AirspaceTimeSlice[@gml:id='ASE_DONLON2_CTA_P'] |
ASE-EX-14 ASE-EX-15 ASE-EX-16 | ATS airspace, TMA, (Airspace aggregation by referencing), Union of two parts (AirspaceVolumeDependency) | //aixm:AirspaceTimeSlice[@gml:id='ASE_MAGNETTO_TMA'] | //aixm:AirspaceTimeSlice[@gml:id='ASE_MAGNETTO1_TMA_P'] | //aixm:AirspaceTimeSlice[@gml:id='ASE_MAGNETTO2_TMA_P'] |
