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The VerticalStructure.group property can be used to indicate that an obstacle consists of a number of closely situated similar objects. This property is not specified in the ICAO PANS-AIM provisions for obstacle data sets, but it might be useful in certain situations, as the ICAO Charting Manual provides a specific symbol for groups of obstacles.
The EUROCAE/RTCA standard for obstacle data sets indicates that vegetation that cannot be captured as individual obstacles should be captured as a polygon. In this case the group = 'YES' indicates that the polygon is actually occupied by a number of similar trees or other vegetation.
Note: If there exists in the middle of the group an obstacle that is significantly higher than the group, this should not be included in the group. That should be still provided as an individual obstacle. As a consequence, the geometry of that individual obstacle (point, line, polygon) intersects the geometry of the group (polygon). This should be kept in mind by data users as a particular case where two obstacles can have intersecting horizontal projections.
The TOD Manual provides guidance on the provision of data for grouping obstacles that have a similar height. Adjacent point obstacles of similar height and elevation can be grouped into an obstacle of type polygon or line. The decision if the objects are captured as single obstacle or as a group depends on the operational needs e.g. if operations are planned or not between obstacles. This is typically the case for windfarms.
Therefore, the group property should be used only for obstacles with polygon (ElevatedSurface) or line (EleveatedCurve) geometry.
Case 1: Polygon (group of wind turbines)
Case where a large number of obstacles with similar elevation are grouped, an area encompassing the grouped obstacles may be published instead of publishing each individual object.
The wind park can be represented as a polygon as shown in the figure below.
In AIXM such as case may be coded as a VerticalStructure consisting of one (or more) VerticalStructurePart with ElevatedSurface geometry and group = 'YES'. The example below shows the encoding of a wind park comprising 8 wind turbines as polygon:
<!-- GROUPS OF OBSTACLES GROUPED WITH AN AREA (POLYGON) (Windfarm area).
Case where a large number of obstacles with similar elevation are grouped, an area encompassing the grouped obstacles may be published instead of publishing each individual object.-->
<aixm:VerticalStructure gml:id="uuid.47db48e9-d46a-4100-a266-25a3968b6a98">
<gml:identifier codeSpace="urn:uuid:">47db48e9-d46a-4100-a266-25a3968b6a98</gml:identifier>
...
<aixm:name>RODSAND II</aixm:name>
<aixm:type>WINDMILL_FARMS</aixm:type>
<aixm:lighted>YES</aixm:lighted>
<aixm:markingICAOStandard>NO</aixm:markingICAOStandard>
<!-- aixm:group is not required by PANS-AIM.
However, in AIXM it is coded with 'YES' in case a single part obstacle is actually a group of several obstacles. -->
<aixm:group>YES</aixm:group>
<aixm:radius xsi:nil="true" nilReason="inapplicable"/>
<aixm:part>
<aixm:VerticalStructurePart gml:id="vsp0002-1">
<aixm:verticalExtent uom="M">115</aixm:verticalExtent>
<aixm:verticalExtentAccuracy uom="M">30</aixm:verticalExtentAccuracy>
<aixm:type>WINDMILL_FARMS</aixm:type>
<aixm:markingFirstColour>GREEN</aixm:markingFirstColour>
<aixm:designator>OBS-0002</aixm:designator>
<aixm:horizontalProjection_surfaceExtent>
<aixm:ElevatedSurface srsName="urn:ogc:def:crs:EPSG::4326" gml:id="ep0002-1">
<gml:patches>
<gml:PolygonPatch>
<gml:exterior>
<gml:Ring>
<gml:curveMember>
<gml:Curve gml:id="c1234">
<gml:segments>
<gml:GeodesicString>
<gml:posList>54.58333333 -24.48555556
54.56222222 -24.61694444
54.52638889 -24.61694444
54.57111111 -24.45777778
54.58333333 -24.48555556</gml:posList>
</gml:GeodesicString>
</gml:segments>
</gml:Curve>
</gml:curveMember>
</gml:Ring>
</gml:exterior>
</gml:PolygonPatch>
</gml:patches>
<aixm:horizontalAccuracy uom="M">50</aixm:horizontalAccuracy>
<aixm:elevation uom="M">115</aixm:elevation>
<aixm:verticalDatum>EGM_96</aixm:verticalDatum>
<aixm:verticalAccuracy uom="M">30</aixm:verticalAccuracy>
</aixm:ElevatedSurface>
</aixm:horizontalProjection_surfaceExtent>
<aixm:lighting>
<aixm:LightElement gml:id="le0002-1">
<aixm:colour>RED</aixm:colour>
<aixm:intensityLevel>LIM</aixm:intensityLevel>
<aixm:type>OTHER:FLASHING</aixm:type>
</aixm:LightElement>
</aixm:lighting>
</aixm:VerticalStructurePart>
</aixm:part>
<!-- The number of obstacles forming the group is coded as annotation. -->
<aixm:annotation>
<aixm:Note gml:id="n12-12">
<aixm:propertyName>group</aixm:propertyName>
<aixm:translatedNote>
<aixm:LinguisticNote gml:id="ln12-12">
<aixm:note lang="eng">8 Wind Turbines</aixm:note>
</aixm:LinguisticNote>
</aixm:translatedNote>
</aixm:Note>
</aixm:annotation>
</aixm:VerticalStructureTimeSlice>
</aixm:timeSlice>
</aixm:VerticalStructure>
</message:hasMember>
Case 2: Line (group of wind turbines)
Another case is the collection of wind turbines as a line. For example, wind turbines positioned over a mountain ridge or offshore may be collected as a line as in the figure below (red line).
In AIXM such as case may be coded as a VerticalStructure consisting of one (or more) VerticalStructurePart with ElevatedCurve geometry and group = 'YES'. The example below shows the encoding a wind park consisting of an unknown amount of wind turbines as one line:
<!-- LINE OBSTACLE (Wind Park) -->
<aixm:VerticalStructure gml:id="uuid.718c2782-a624-405e-86b6-144b40b680b0">
<gml:identifier codeSpace="urn:uuid:">718c2782-a624-405e-86b6-144b40b680b0</gml:identifier>
...
<aixm:name>TUBORG IIB</aixm:name>
<aixm:type>WINDMILL_FARMS</aixm:type>
<aixm:lighted>YES</aixm:lighted>
<aixm:markingICAOStandard>NO</aixm:markingICAOStandard>
<aixm:group>YES</aixm:group>
<aixm:radius xsi:nil="true" nilReason="inapplicable"/>
<aixm:part>
<aixm:VerticalStructurePart gml:id="vsp0006-1">
<aixm:verticalExtent uom="M">75</aixm:verticalExtent>
<aixm:verticalExtentAccuracy uom="M">30</aixm:verticalExtentAccuracy>
<aixm:type>WINDMILL_FARMS</aixm:type>
<aixm:markingFirstColour>GREEN</aixm:markingFirstColour>
<aixm:designator>OBS-00006</aixm:designator>
<aixm:horizontalProjection_linearExtent>
<aixm:ElevatedCurve srsName="urn:ogc:def:crs:EPSG::4326" gml:id="crv12456">
<gml:segments>
<gml:GeodesicString>
<gml:posList>54.33333333 -26.48555556 54.33777778 -26.45777778</gml:posList>
</gml:GeodesicString>
</gml:segments>
<aixm:horizontalAccuracy uom="M">50</aixm:horizontalAccuracy>
<aixm:elevation uom="M">75</aixm:elevation>
<aixm:verticalDatum>EGM_96</aixm:verticalDatum>
<aixm:verticalAccuracy uom="M">30</aixm:verticalAccuracy>
</aixm:ElevatedCurve>
</aixm:horizontalProjection_linearExtent>
<aixm:lighting>
<aixm:LightElement gml:id="le0006-1">
<aixm:colour>RED</aixm:colour>
<aixm:intensityLevel xsi:nil="true" nilReason="unknown"/>
<aixm:intensity xsi:nil="true" nilReason="unknown"/>
<aixm:type>OTHER:FLASHING</aixm:type>
<aixm:availability xsi:nil="true" nilReason="unknown"/>
</aixm:LightElement>
</aixm:lighting>
</aixm:VerticalStructurePart>
</aixm:part>
</aixm:VerticalStructureTimeSlice>
</aixm:timeSlice>
</aixm:VerticalStructure>
</message:hasMember>
Case 3: Series of points (not a group)
There may be an operational benefit to collect and represent each wind turbines of a wind park as an individual obstacle.
In AIXM there two possibility to encode such a case:
Option A. The wind park as such is encoded as one VerticalStructure. Each
Option B: Each individual wind turbine is encoded as its own VerticalStructure. The wind turbines are not related to each other. (see Single Wind Turbine).
The example below shows the encoding of Option A:
<!-- GROUPS OF OBSTACLES EACH OBSTACLE PUBLISHED INDIVIDUALLY (Wind turbines of a windpark). -->
<aixm:VerticalStructure gml:id="uuid.6c7fac45-c24f-4e36-b196-687458d99070 ">
<gml:identifier codeSpace="urn:uuid:">6c7fac45-c24f-4e36-b196-687458d99070</gml:identifier>
...
<aixm:name>WINDPARK BAUMGARTEN</aixm:name>
<aixm:type>WINDMILL_FARMS</aixm:type>
<aixm:lighted>NO</aixm:lighted>
<aixm:markingICAOStandard>OTHER:NOT_MARKED</aixm:markingICAOStandard>
<aixm:radius xsi:nil="true" nilReason="inapplicable"/>
<!-- Windturbine 1 of the Windpark-->
<aixm:part>
<aixm:VerticalStructurePart gml:id="vsp0003-1">
<aixm:verticalExtent uom="M">150</aixm:verticalExtent>
<aixm:verticalExtentAccuracy uom="M">30</aixm:verticalExtentAccuracy>
<aixm:type>WINDMILL</aixm:type>
<aixm:designator>OBS-0003-1</aixm:designator>
<aixm:horizontalProjection_location>
<aixm:ElevatedPoint srsName="urn:ogc:def:crs:EPSG::4326" gml:id="ep0003-1">
<gml:pos>47.74500000 -27.52583333</gml:pos>
<aixm:horizontalAccuracy uom="M">50</aixm:horizontalAccuracy>
<aixm:elevation uom="M">264</aixm:elevation>
<aixm:verticalDatum>EGM_96</aixm:verticalDatum>
<aixm:verticalAccuracy uom="M">30</aixm:verticalAccuracy>
</aixm:ElevatedPoint>
</aixm:horizontalProjection_location>
</aixm:VerticalStructurePart>
</aixm:part>
<!-- Windturbine 2 of the Windpark-->
<aixm:part>
<aixm:VerticalStructurePart gml:id="vsp0003-2">
<aixm:verticalExtent uom="M">150</aixm:verticalExtent>
<aixm:verticalExtentAccuracy uom="M">30</aixm:verticalExtentAccuracy>
<aixm:type>WINDMILL</aixm:type>
<aixm:designator>OBS-0003-2</aixm:designator>
<aixm:horizontalProjection_location>
<aixm:ElevatedPoint srsName="urn:ogc:def:crs:EPSG::4326" gml:id="ep0003-2">
<gml:pos>47.74222222 -27.52388889</gml:pos>
<aixm:horizontalAccuracy uom="M">50</aixm:horizontalAccuracy>
<aixm:elevation uom="M">253</aixm:elevation>
<aixm:verticalDatum>EGM_96</aixm:verticalDatum>
<aixm:verticalAccuracy uom="M">30</aixm:verticalAccuracy>
</aixm:ElevatedPoint>
</aixm:horizontalProjection_location>
</aixm:VerticalStructurePart>
</aixm:part>
<!-- Windturbine 3 of the Windpark-->
<aixm:part>
<aixm:VerticalStructurePart gml:id="vsp0003-3">
<aixm:verticalExtent uom="M">150</aixm:verticalExtent>
<aixm:verticalExtentAccuracy uom="M">30</aixm:verticalExtentAccuracy>
<aixm:type>WINDMILL</aixm:type>
<aixm:designator>OBS-0003-3</aixm:designator>
<aixm:horizontalProjection_location>
<aixm:ElevatedPoint srsName="urn:ogc:def:crs:EPSG::4326" gml:id="ep0003-3">
<gml:pos>47.74194444 -27.528888896</gml:pos>
<aixm:horizontalAccuracy uom="M">50</aixm:horizontalAccuracy>
<aixm:elevation uom="M">255</aixm:elevation>
<aixm:verticalDatum>EGM_96</aixm:verticalDatum>
<aixm:verticalAccuracy uom="M">30</aixm:verticalAccuracy>
</aixm:ElevatedPoint>
</aixm:horizontalProjection_location>
</aixm:VerticalStructurePart>
</aixm:part>
<!-- Windturbine 4 of the Windpark-->
<aixm:part>
<aixm:VerticalStructurePart gml:id="vsp0003-4">
<aixm:verticalExtent uom="M">150</aixm:verticalExtent>
<aixm:verticalExtentAccuracy uom="M">30</aixm:verticalExtentAccuracy>
<aixm:type>WINDMILL</aixm:type>
<aixm:designator>OBS-0003-4</aixm:designator>
<aixm:horizontalProjection_location>
<aixm:ElevatedPoint srsName="urn:ogc:def:crs:EPSG::4326" gml:id="ep0003-4">
<gml:pos>47.73888889 -27.52750000</gml:pos>
<aixm:horizontalAccuracy uom="M">50</aixm:horizontalAccuracy>
<aixm:elevation uom="M">239</aixm:elevation>
<aixm:verticalDatum>EGM_96</aixm:verticalDatum>
<aixm:verticalAccuracy uom="M">30</aixm:verticalAccuracy>
</aixm:ElevatedPoint>
</aixm:horizontalProjection_location>
</aixm:VerticalStructurePart>
</aixm:part>
<!-- Windturbine 5 of the Windpark-->
<aixm:part>
<aixm:VerticalStructurePart gml:id="vsp0003-5">
<aixm:verticalExtent uom="M">150</aixm:verticalExtent>
<aixm:verticalExtentAccuracy uom="M">30</aixm:verticalExtentAccuracy>
<aixm:type>WINDMILL</aixm:type>
<aixm:designator>OBS-00003-5</aixm:designator>
<aixm:horizontalProjection_location>
<aixm:ElevatedPoint srsName="urn:ogc:def:crs:EPSG::4326" gml:id="ep0003-5">
<gml:pos>47.73888889 -27.43361111</gml:pos>
<aixm:horizontalAccuracy uom="M">50</aixm:horizontalAccuracy>
<aixm:elevation uom="M">269</aixm:elevation>
<aixm:verticalDatum>EGM_96</aixm:verticalDatum>
<aixm:verticalAccuracy uom="M">30</aixm:verticalAccuracy>
</aixm:ElevatedPoint>
</aixm:horizontalProjection_location>
</aixm:VerticalStructurePart>
</aixm:part>
</aixm:VerticalStructureTimeSlice>
</aixm:timeSlice>
</aixm:VerticalStructure>
