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Subject: FYI: Discussion of the OSAIS GML where profile and the OGC GML Simple Features profile.
At the last OASIS EM TC GIS Subcommittee call, we had an excellent
discussion on encoding requirements for geospatial content in OASIS EM
standards. The discussion included new requirements, such as geopolitical
boundaries with attributes (properties), what the OASIS GML "where" profile
supports and does not support, and what NENA and the IETF have been
doing. I also spoke briefly about the OGC Simple Features GML profile. The
attached document discusses the key concepts related to the GML
information model: Geometry and Feature. Please read this document before
moving onto the following discussion.
The OASIS GML Where profile as implemented according to OASIS EM
requirements (also attached) is a set of geometry elements. There is no concept
of feature (although the schema could be easily extended to include the feature
model). Since feature is not part of the OASIS GML where profile as defined, you
can only encode geometries and some metadata (coordinate reference systems) and
not features. So, layers of map data such as geopolitical boundaries that
include names and other attributes cannot be encoded using the OASIS GML Where
profile. A separate encoding would be required.
Conversely, if a GML profile includes the feature model, then not only
geometries but features can be encoded. So geopolitical boundaries with names
and other attributes (population, contact names, etc) or a plume geometry could
also include time and date stamps, plume type, plume direction, model name used
to generate the plume model, and so for than be encoded using GML.
The OGC has an existing standard called OGC GML Simple Features profile.
This profile is available for GML 3.1.1 and GML 3.2. GML 3.2 is the joint
OGC/ISO standard. The profile support numerous geometries as well as the full
feature model. The geometry types supported are: points, multipoints,
linestrings, curves, polygons (surface), multicurve, multisurface, and agregates
(combinations of all of these types). The only type as specified in the OASIS EM
requirements for a geospatial encoding that is not supported is type "circle".
GML supports multiple methods for expressing circles but the Simple Features
profile does not include that element. However, there is already an OGC change
request to add circle to GML Simple Features. http://portal.opengeospatial.org/files/?artifact_id=39853 to
download the OGC standard.
Now, obviously, GML Simple Features would introduce additional complexity
in that more types as well as the Feature Model are supported. However, the
standard actually specifies three conformance levels. These are described at the
bottom of the attached document on GML. The most restrictive level is level 0.
Level 0 is fairly lightweight and fairly easy to implement.
An example of the use of the GML Simple Features standard is the XML schema
and encoding data for the NENA NG 911 GIS model. Last Friday I uploaded these
documents to the OASIS document archive and sent an email with the links. NENA
decided os this approach because ALL of the geospatial technology providers that
sell GIS solutions to the local government in the US and Canada support the
ability to ingest GML encoded payloads. The NENA GIS model includes geopolitical
(jurisdictional) boundaries.
There are a number of other important aspects of GML SF. These include
support for feature collections, internationalization, metadata, measurements,
and dictionaries (code lists). An example of a GML SF encoding is included in
the NENA documents.
Regards
Carl Reed, PhD
The OGC: Making Location Count!
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2010 GML Information for OASIS EM TC.doc
2009 September OASIS where GML profile requirements v 2 20101016 pxs-ojn.doc
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