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.
This results in three typical coding situations, as described in the following sub-sections:
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Types for Airspace Geometry Components
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 operationequal-to 'SUBTR', operationSequenceequal-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.
The figure below shows an example. The geometry of the "child" airspace which derives the geometry from the "parent" airspace(s) may be
- a composition by aggregation of airspace (e.g. union and subtraction operations).
.
The parent airspace(s) always determine(s) the geometry of the child airspace, i.e. the parent airspace has already a specified geometry which will be inherited by the child.
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 | ||
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| 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. | ||
| Note | ||
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| In case of a simple "above-below" composition, operation and operationSequence will be left empty. |
Airspace Aggregation - Copying Geometry vs. Referencing
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.
| Note | ||
|---|---|---|
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| 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). 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:
There is an additional option here. Instead of coping the geometry of the 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 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 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.
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).
The figure below illustrates a simple referencing, again using as example the BRUSSELS TMA with its two parts: TMA one and TMA two.
| Code Block | ||||||||
|---|---|---|---|---|---|---|---|---|
| ||||||||
<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> |
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 dependency is coded as 'HORZ_PROJECTION'. That means that the subtraction is limited to the horizontal projection. Hence, the vertical limits of The "SUBTR2" has its own defined upperLimit and lowerLimit, which equals the vertical limits defined for "BASE1".
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".
Example 1-2:
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.
ASE-EX-11
ASE-EX-12
ASE-EX-13
//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//aixm:AirspaceTimeSlice[@gml:id='ASE_MAGNETTO_TMA'] |
//aixm:AirspaceTimeSlice[@gml:id='ASE_MAGNETTO1_TMA_P'] |
//aixm:AirspaceTimeSlice[@gml:id='ASE_MAGNETTO2_TMA_P']