Carl,
Thanks for this update and summary of the issues and status of the
candidate standards and profiles for the TC to consider going
forward.
I encourage everyone to review this material as well as the posts Carl
has made to the document repository. This is core information in
all of our EDXL work and we need to be sure to understand the issues and
available paths forward in order to make a decision going forward.
Regards,
Elysa
At 08:40 PM 11/8/2010, Carl Reed wrote:
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
CTO and Executive Director Specification Program
Open Geospatial Consortium
www.opengeospatial.org
The OGC: Making Location Count!
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