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Copyright © 2013 Open Geospatial Consortium.
server to return a set of disjoint GML surfaces that represent the original airspace. Additionally, airspaces contain altitude data. This cannot be modeled by GML. Currently,
the team is discussing the creation of a custom GML schema that explicitly models the altitude. Therefore the support of altitudes within this profile had no absolute guarantee
within OWS-9.
8.2.3.1 Inputs
The Inputs for this process are one AIXM feature and an optional date time. The date time is used to resolve the geometry of the feature for a specific valid time. If it is not
provided, this input defaults to the current time.
The input AIXM feature has two supported variants: Inline or by reference. The inline variant the default allows clients to supply the AIXM feature in its entirety, embedded
into the WPS execute.
The ‘by reference’ variant makes use of a newly developed AIXM extension schema. This schema allows AIXM features to be referenced to by their GML identifier. Section
8.2.3.6 contains the proposed AIXM extension schema.8.2.3.6
See Section 7 for the list of supported input AIXM features.
8.2.3.2 Outputs
The output of this process is an element as defined within the Geometry Aggregates subschema of GML 3.2.
8.2.3.3 Algorithm
The geometry retrieval algorithm consists of several phases. First, if the given input feature is a reference i.e. If it uses the schema in section 8.2.3.6,
the feature for the reference is resolved on the server. This is accomplished with a GetFeature query that contains a list of all feature type names supported by the server.
This feature is needed because based on the reference, we cannot know what type of feature we are dealing with. It is important to know the feature type, as different features
will link to geometry in different ways.
Next, using the resolved or given feature, we first have a look at the type of feature we are dealing with. This part of the algorithm is highly format dependent. For example, a
Taxiway feature contains an associated AirportHeliport, which contains a point-based geometry. However, this geometry is only secondary information. What we’re really
interested in is the collection of TaxiwayElement features that have the given Taxiway as associated Taxiway through reverse association.
Copyright © 2013 Open Geospatial Consortium.
79 Another example would be a RouteSegment, which contains a GML curve, as well as
separate start and end positions. Generally speaking, we are only interested in obtaining the GML curve that represents the RouteSegment.
We make a distinction between AIXM features that contain their primary geometry directly versus AIXM features that do not contain their primary geometry directly. Two
examples of AIXM features that contain their primary geometry directly are Airspaces and RouteSegments.
When a given feature does not directly contain its primary geometry, we have to perform an additional query on the WFS server to resolve a set of new features that do contain the
necessary geometry. Many of the examined features made use of reverse associations. For example, Runway has no links to RunwayElements, but RunwayElement features do
have links to Runways in the form of associations. For OWS9, we have implemented support for the following features:
Runway → RunwayElement Apron → ApronElement
Taxiway → TaxiwayElement For this we make use of the wfs:valueOf function, as documented in paragraph 7.3.2 of
the WFS 2.0 specification. The wfs:valueOf allows us to retrieve the XLink value of a property. This means that we can easily create a filter that finds all RunwayElements with
a link to our original Runway feature. An example of what this WFS query would look like can be seen in the query below:
wfs:Query xmlns:aixm=http:www.aixm.aeroschema5.1 typeNames=aixm:RunwayElement fes:Filter
fes:PropertyIsEqualTo fes:ValueReferencewfs:valueOfaixm:associatedRunwaygml:identifierfes:ValueRef
erence fes:Literal009AA70D-C240-4A66-9873-9ADC1F744C76fes:Literal
fes:PropertyIsEqualTo fes:Filter
wfs:Query
Finally, after all necessary features are retrieved, we generate a SNAPSHOT timeslice on the results, based on the given input date. For more information on SNAPSHOT
generation, please see the AIXM 5.1 temporality model documentation.
8.2.3.4 Unique identifier
