The horizontal boundary of some airspace may be derived from the horizontal boundary of another airspace. A typical examples are UIR that inherit the horizontal limits of an FIR.

The geometry of such (dependent) airspace can be coded with a single AirspaceVolume, which has its own vertical limits but which does not have its own horizontalProjection. Instead, the AirspaceVolume needs the contributorAirspace and its AirspaceVolumeDependency association class properties (dependency = 'HORZ_PROJECTION'). Note that the operation and operationSequence attributes of the AirspaceComponentGeometry association class shall not be left empty. They should get the values 'BASE' and '1', respectively.

Note: The model offers an additional (theoretical) possibility - that an AirspaceVolume inherits the complete geometry (both horizontal projection and vertical limits) of another Airspace (dependency = 'FULL_GEOMETRY'). However, there are no known usages of this possibility for single volume airspace. This possibility is expected to be used only for airspace defined with Multiple volumes.

Coding Example

The figure below shows a simple example of such an airspace.

The lateral limits of the UIR YORK NEW are derived from the horizontal projection defined for the FIR YORK NEW. Dedicated vertical limits (FL 180 - UNL)  are defined for the UIR YORK NEW.

Note

This is a fictitious example part of the AIXM DONLON Specimen 2022. 



XML snippet 
 <!-- FIR YORK NEW -->
        <aixm:Airspace gml:id="uuid.b75a32cf-65da-4028-81f2-70ad30072736">
		...
                <aixm:type>FIR</aixm:type>
                <aixm:designator>KAAD</aixm:designator>
                <aixm:name>YORK NEW</aixm:name>
                <aixm:designatorICAO>YES</aixm:designatorICAO>
                <aixm:class>
                    <aixm:AirspaceLayerClass gml:id="alc0001">
                        <aixm:annotation>
                            <aixm:Note gml:id="n0001">
                                <aixm:propertyName>classification</aixm:propertyName>
                                <aixm:purpose>REMARK</aixm:purpose>
                                <aixm:translatedNote>
                                    <aixm:LinguisticNote gml:id="ln00011">
                                        <aixm:note>Outside regulated airspace.</aixm:note>
                                    </aixm:LinguisticNote>
                                </aixm:translatedNote>
                            </aixm:Note>
                        </aixm:annotation>
                        <aixm:classification>G</aixm:classification>
                    </aixm:AirspaceLayerClass>
                </aixm:class>
                <aixm:protectedRoute xsi:nil="true"/>
                <aixm:geometryComponent>
                    <aixm:AirspaceGeometryComponent gml:id="A-cd43e44a">
                        <aixm:theAirspaceVolume>
                            <aixm:AirspaceVolume gml:id="A-c3969fee">
                                <aixm:upperLimit uom="FL">180</aixm:upperLimit>
                                <aixm:lowerLimit>GND</aixm:lowerLimit>
                                <aixm:horizontalProjection>
                                    <aixm:Surface srsName="urn:ogc:def:crs:EPSG::4326"
                                        gml:id="s0010">
                                        <gml:patches>
                                            <gml:PolygonPatch>
                                                <gml:exterior>
                                                    <gml:Ring>
                                                        <gml:curveMember>
                                                            <gml:Curve gml:id="c0010">
                                                                <gml:segments>
                                                                    <gml:GeodesicString>
                                                                        <gml:posList>57.0833333333333 -40 
                                                                            52.85 -41.7833333333333 
                                                                            48.4666666666667 -41.3333333333333 
                                                                            44.0333333333333 -40 
                                                                            42.6 -37 
                                                                            40.7333333333333 -37.1833333333333 
                                                                            41.8765247129238 -52.7268162084394 
                                                                            56.1244400919614 -46.3306297361232 
                                                                            57.0833333333333 -40</gml:posList>
                                                                    </gml:GeodesicString>
                                                                </gml:segments>
                                                            </gml:Curve>
                                                        </gml:curveMember>
                                                    </gml:Ring>
                                                </gml:exterior>
                                            </gml:PolygonPatch>
                                        </gml:patches>
                                        <aixm:horizontalAccuracy uom="KM"
                                            >2.0</aixm:horizontalAccuracy>
                                    </aixm:Surface>
                                </aixm:horizontalProjection>
                            </aixm:AirspaceVolume>
                        </aixm:theAirspaceVolume>
                    </aixm:AirspaceGeometryComponent>
                </aixm:geometryComponent>
            </aixm:AirspaceTimeSlice>
        </aixm:timeSlice>
    </aixm:Airspace>

    <!-- UIR YORK NEW, derived geometry from FIR YORK NEW -->   

      <aixm:Airspace gml:id="uuid.6fa9b51a-ea66-40a7-a23a-058c3a034719">
          <gml:identifier codeSpace="urn:uuid:">6fa9b51a-ea66-40a7-a23a-058c3a034719</gml:identifier>
           ...
                    <aixm:type>UIR</aixm:type>
                    <aixm:designator>KAAD</aixm:designator>
                    <aixm:name>YORK NEW</aixm:name>
                    <aixm:designatorICAO>YES</aixm:designatorICAO>
                    <aixm:class>
                        <aixm:AirspaceLayerClass gml:id="alc1001">
                            <aixm:classification>C</aixm:classification>
                        </aixm:AirspaceLayerClass>
                    </aixm:class>
                    <aixm:protectedRoute xsi:nil="true"/>
                    <aixm:geometryComponent>
                        <aixm:AirspaceGeometryComponent
                            gml:id="data1000212">
                            <aixm:operation>BASE</aixm:operation>
                            <aixm:operationSequence>1</aixm:operationSequence>
                            <aixm:theAirspaceVolume>
                                <aixm:AirspaceVolume gml:id="data1000424423">
                                    <aixm:upperLimit>UNL</aixm:upperLimit>
                                    <aixm:lowerLimit uom="FL">180</aixm:lowerLimit>
                                    <aixm:contributorAirspace>
                                        <aixm:AirspaceVolumeDependency
                                            gml:id="data100024324">
                                            <aixm:dependency>HORZ_PROJECTION</aixm:dependency>
                                            <aixm:theAirspace xlink:href="urn:uuid:b75a32cf-65da-4028-81f2-70ad30072736" xlink:title="FIR YORK NEW"/>
                                        </aixm:AirspaceVolumeDependency>
                                    </aixm:contributorAirspace>
                                </aixm:AirspaceVolume>
                            </aixm:theAirspaceVolume>
                        </aixm:AirspaceGeometryComponent>
                    </aixm:geometryComponent>
                </aixm:AirspaceTimeSlice>
            </aixm:timeSlice>
        </aixm:Airspace>


This coding examples can be found in the AIP Data Set - Specimen (DONLON).

No.DescriptionXPath Expression
ASE-EX-20UIR with derived lateral limits from FIR (Single volume with derived geometry)

//aixm:AirspaceTimeSlice[@gml:id='ASE_YORKNEW_UIR']


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