Copyright © 2013 Open Geospatial Consortium.
65 In aviation-specific applications, limiting the use of bandwidth is always an important
goal. Therefore, this functionality defined an extension schema referring to AIXM 5.1 which allows the provision of a feature identifier see Listing 6. This can be considered
as referring to a uniquely identified feature within a WFS server instance
1
. The implementation is linked to Aviation Processing work area see section 8.
Listing 6 - Feature by Identifier Reference.
?xml version=1.0 encoding=UTF-8? wfs:GetFeature service=WFS version=2.0.0
outputFormat=applicationgml+xml; version=3.2 ... wfs:Query typeNames=avwx:SIGMET handle=Q01
fes:Filter fes:Intersects
fes:ValueReferencewfs-aixm:extentOf.fes:ValueReference aixm-ext:FeatureIdentifier
aixm-ext:identifier codeSpace=urn:uuid: 4fd9f4be-8c65-43f6-b083-3ced9a4b2a7f
aixm-ext:identifier aixm-ext:FeatureIdentifier
fes:Intersects fes:Filter
wfs:Query wfs:GetFeature
7.4.4.3 Implementation
Within OWS-9 it was agreed that the WFS instances would implement the functionality inside their own services since relying on an external service is not preferable for data
stores which are intended to be stable and reliable.
The Event Service instances make use of the “Geometry Retrieval” WPS Profile. At the time of subscription at the service, a WPS Execute request with the AIXM Feature placed
inline or referenced see Listing 7Error Reference source not found.. As the result is a GML 3.2 geometry, the ES instances were then able to treat it as a common geometry.
Listing 7 – Exemplary Geometry Retrieval WPS Request.
wps:Execute service=WPS version=1.0.0
xmlns:wps=http:www.opengis.netwps1.0.0 xmlns:ows=http:www.opengis.netows1.1
xmlns:aixm=http:www.aixm.aeroschema5.1 xmlns:aixm-ext=http:www.opengis.netows9aviationaixmextension
xsi:schemaLocation=http:www.aixm.aeroschema5.1 http:test.schemas.opengis.netows-9aviationaixm5.1AIXM_Features.xsd
http:www.opengis.netows9aviationaixmextension http:test.schemas.opengis.netows- 9aviationaixmaixm-extension.xsd
ows:IdentifierResolveAIXMFeatureGeometryows:Identifier wps:DataInputs
wps:Input ows:IdentifierFeatureows:Identifier
wps:Data wps:ComplexData
aixm-ext:FeatureIdentifier aixm-ext:identifier codeSpace=urn:uuid:4fd9f4be-8c65-43f6-b083-
3ced9a4b2a7faixm-ext:identifier
1
The built-in join functionality of the WFS specification is not as compact, as it always returns both join partners.
66
Copyright © 2013 Open Geospatial Consortium.
aixm-ext:FeatureIdentifier wps:ComplexData
wps:Data wps:Input
wps:DataInnputs wps:Execute
7.4.4.4 Retrieval of WXXM Data
Within OWS-9, this feature was only implemented to retrieve AIXM-encoded data. However, another interesting application is the filtering of WXXM-formatted data e.g.
provided through a WFS or WCS. This section provides some insights about possible benefits and drawbacks when realizing such functionality.
In situations where the AIXM feature that is used as geometry operand is referenced instead of given inline and if that feature is not known to the service because it is not
stored there, the AIXM feature as geometry operand functionality does not work – unless, of course, the WXXM-WFS can dynamically discover said feature.
Additionally, as this feature is currently implemented using WFS spatial joins, it could add an additional effort to provided support for both encodings in spatial joins. However,
spatial joins allow more compact results as no tuples are returned which would ease the processing of a result.
The following table summarizes additional pros and cons of such an approach.
Pros Cons
Easier execution of WFS GetFeature filters to retrieve
WXXM data that satisfy a spatial constraint, especially if
that spatial constraint is based upon the spatial extent of an
AIXM feature e.g. a route, an airspace, an ARTCC.
WXXM - providing WFS today often do not have knowledgesupport for AIXM
features – adding the AIXM feature as geometry operand functionality as an
implementation requirement thus creates additional implementation burden. This
may be mitigated by the design of a cascadingadapting WFS which has
access to both a WFS with WXXM data and a WFS with AIXM data or has that
already and which realizes the AIXM feature as geometry operand functionality.
7.4.5 Event Service Update Intervals
