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

CTO and Executive Director Specification Program
Open Geospatial 
Consortium
www.opengeospatial.org

 

The OGC: Making Location Count!

 

---------------------

 

This communication, including attachments, is for the exclusive use of 
addressee and may contain proprietary, confidential or privileged information. 
If you are not the intended recipient, any use, copying, disclosure, 
dissemination or distribution is strictly prohibited. If you are not the 
intended recipient, please notify the sender  immediately by return email 
and delete this communication and destroy all copies.

 

"The important thing is not to stop questioning." -- Albert Einstein 

"Security is mostly a superstition. It does not exist in nature. Life is 
either a daring adventure or nothing." -- Helen Keller 

2010 GML Information for OASIS EM TC.doc

2009 September OASIS where GML profile requirements v 2 20101016 pxs-ojn.doc