[geotk] Report from Barcelona OGC meeting

Martin Desruisseaux martin.desruisseaux at geomatys.fr
Sun Mar 15 17:38:53 PDT 2015


Hello all

Last week was the OGC meeting in Barcelona [1]. Below are some points
that attracted my attention. Note that the next OGC meeting will be in
Boulder (Colorado) in June.

Table of content:

  * API ad-hoc and GeoAPI
  * Standard openness ad-hoc
  * OGC and W3C on GeoSemantic
  * Metadata and data preservation
  * Metadata validation
  * Coordinate Reference System (CRS)
  * Moving features
  * Coverage and GML
  * Varia

[1] http://www.opengeospatial.org/event/1503tcagenda


      API ad-hoc and GeoAPI

First, we had a review of current situation: many Java projects
currently derive their API from OGC's XSD files, but this lead to poor
API. The "covariant type" and the "union" language features were used as
examples illustrating the problems. Next we had a discussion about
whether OGC wants to define an API derived from UML, and (if yes) which
kind of API it would be. For example an OGC's API shall not imply any
particular implementation. This neutrality is possible in Java thanks to
interfaces, but not in JavaScript for example. The discussion will
continue in next OGC meeting.

The GeoAPI working group will probably stay in a "stand by" position,
waiting for OGC to clarify their plan. Some work may continue on GitHub
for bug fixes, documentation clarifications or tests, but no new
features would start for now.

Note that some other standards (e.g. Moving Feature version 2) are
considering to define an API as part of their work. I do not know yet if
those API could be integrated with GeoAPI.


      Standard openness ad-hoc

The discussion covers two aspects:

  * How to attract open source communities while preserving conformance
    to the standards.
  * How to maintain OGC standards baseline while supporting potentially
    disruptive new technologies. For GeoAPI, this can be related to the
    split of development work in a GeoAPI 3.1 and 4.0 branches [2].

This is an effort underway for 3 years. The "Ideas4OGC" call [3] is part
of this effort. Discussion will continue in next OGC meeting.

[2] http://www.geoapi.org/snapshot/index.html
[3] http://external.opengeospatial.org/twiki_public/Ideas4OGC/WebHome


      OGC and W3C on GeoSemantic

W3C already produced a standard using OGC/ISO standards: Provenance
ontology [4], which is now formally a W3C standard since April 2013.
This standard uses the ISO 19115 "lineage" package, which we support in
Apache SIS [5]. This means that we already have some ground for
implementation of W3C's PROV-O standard if wanted.

For the next tasks, OGC and W3C consortium will work together on the
following (among other tasks) [6]:

  * Best practices (where there are too many choices).
  * Ontology for Gregorian calendar and temporal relationship, based on
    Allen's interval calculus. They will seek for harmonization between
    OWL-time standard [7] and ISO 19108 [8], but we do not yet know how.
    For GeoAPI, this will impact the org.opengis.temporal package
    (currently in the "pending" part of GeoAPI).
  * Spatial data encoding, relation, identity, geometry and API. They
    are collecting requirements for an API design (I'm not sure which
    kind of API) and currently have more than 25 use cases.

More information on the planed work can be found at [9]. OGC and W3C are
considering to hold a GeoSemantic summit which would be open to anyone
(not an OGC-members meeting). The meeting may be held in June (in which
case it would be together with OGC at Boulder), maybe later - it is not
yet sure.

[4] http://www.w3.org/TR/prov-o/
[5] http://sis.apache.org/apidocs/org/apache/sis/metadata/iso/lineage/package-summary.html
[6] http://www.w3.org/2015/spatial/charter
[7] http://www.w3.org/TR/owl-time/
[8] http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=26013
[9] http://www.w3.org/2015/spatial/wiki/Main_Page


      Metadata and data preservation

The goal is to establish a digital preservation metadata model that
allows documenting the necessary features to ensure the durability of
the information. They were a discussion on some existing efforts:

  * Since 1998: Earth Science Information Partners (ESIP)
  * Since 2004: Digital Curation Centre (DCC)
  * Since 2011: Geospatial Multistate Archive and Preservation
    Partnership (GeoMAPP)
  * Since 2013: Research Data Alliance (RDA)
  * Open Archival Information System (OAIS)
  * PREMIS data dictionary
  * (under development): ISO 19165 - Preservation of digital data and
    metadata

The OAIS standard (also known as ISO 14721) is a conceptual model; it
does not define which attribute to use exactly. The PREMIS data
dictionary is an effort to combine OAIS and ISO 19115 (metadata)
standards to obtain a more concrete schema, completed with some GeoMAPP
ideas. Again, given Apache SIS support of ISO 19115, if we wanted to
address data preservation issues, maybe PREMIS would be a good entry
point. I do not know however what would be the relationship with the ISO
19165 standard under development.


      Metadata validation

The CINERGI project (Inventory of EarthCube Resources for Geoscience
Interoperability) provides tests for ISO 19115 metadata objects, which
can be run as TestNG tests [10]. There is an overlap between those tests
and the one provided by GeoAPI and used by Apache SIS. However the
CINERGI tests are designed for validating XML files, while GeoAPI
conformance module is designed for validating Java objects. It may be
worth to consider to port or adapt some CINERGI code (they are under
Apache 2 license) in order to use their schematron files for validating
our metadata instances. CINERGI seems to execute the following scripts:

  * org/opengis/cite/schematron/iso19139_schematron_nil.sch
  * org/opengis/cite/schematron/checkEncodingStandard.sch
  * org/opengis/cite/schematron/checkDataIdentification.sch
  * org/opengis/cite/schematron/checkAggregateInformation.sch
  * org/opengis/cite/schematron/checkLegalConstraints.sch
  * org/opengis/cite/schematron/checkScopeOfXmlFile.sch
  * org/opengis/cite/schematron/checkGeorectified.sch
  * org/opengis/cite/schematron/checkBandValueOfXml.sch
  * org/opengis/cite/schematron/checkMediumOfXml.sch
  * org/opengis/cite/schematron/checkExtendedElementInformation.sch
  * org/opengis/cite/schematron/checkExtentValueOfXml.sch
  * org/opengis/cite/schematron/checkResponsiblePartyOfXml.sch

However I don't know where to find them (they are not in GeoAPI). Does
anyone has some clues?

Note: OGC is using Geotk for some of their tests, with a note saying
that significant chunks of Geotk code is moving to Apache SIS [11].

[10] https://github.com/opengeospatial/ets-19139
[11] http://opengeospatial.github.io/geomatics-geotk/


      Coordinate Reference System (CRS)

The Well Known Text (WKT) version 2 (ISO 19162) working group has
completed his work and has been dissolved. The WKT 2 implementation is
under way in Apache SIS. However WKT 2 has known limitations on temporal
reference systems. In particular, there is currently no standard way to
define the calendar in use. The intend is not to support the calendars
in use in various cultures (we can use java.time or JODA for that
purpose), but rather to support some "scientific" calendars like the
360-days long years used in climatology, or 365-days long years without
leap years, etc. I think that the discussion will continue in next OGC
meetings.

A new topic on the table is a proposal to define a standard file format
for the exchange of gridded geodetic data. We are currently seeing:

  * More lat-long offset grids (used for datum shifts)
  * More geoid and height correction models
  * More velocity and deformation grids

But no standard file format exists. NADCON, NTv2, EGM96, etc. are in
common use but not standard. The proposal is to create a working group
in the next OGC meeting for addressing this issue.

An other possible next work may be a revision of ISO 19111 data model.
In particular, there is a proposal to refine compound CRS when a
vertical transformation depends on horizontal parts. For Apache SIS,
this may impact the DefaultCompoundCRS class [12] among others.

[12] http://sis.apache.org/apidocs/org/apache/sis/referencing/crs/DefaultCompoundCRS.html


      Moving features

The moving feature standard has been completed and published on February
17th [13]. Current standard focus on XML and CSV file formats. There is
plan to work for a version 2 which would add a simple binary file format
(maybe NetCDF), GeoJSON and an API for data exchange.

[13] http://www.opengeospatial.org/standards/movingfeatures


      Coverage and GML

We currently have two closely-related, but still different, coverage
models: ISO 19123 and GML. The GML model is defined in an OGC standard
currently named "GMLCOV", which is misleading. Despite its name,
"GMLCOV" is not really a GML encoding of ISO 19123 coverages. GMLCOV is
an implementation model for the abstract coverage model defined by ISO
19123. So a better name for "GMLCOV" may be "Geographic information -
implementation schema for coverages".

Work for unifying ISO and GML models started in 2012. The coverages as
expressed in GMLCOV has evolved since when ISO 19123 was originally
written (in 2005). So the ISO standard may need to be review. However it
would probably be only a few small changes to clauses like the
description of discrete coverage - ISO 19123 is not broken. There is a
proposal to bring GMLCOV to ISO, maybe as part 2 of ISO 19123.

If I understand correctly, the ISO 19163 standard ("Geographic
information - Content components and encoding rules for imagery and
gridded data”) would be a specialization of ISO 19123 for one very
common type of coverage data: remote sensing imagery, together with
links to other relevant standards [14]. The ISO 19163 standard would
have at least two parts: 1) content model, and 2) application to
existing formats like GeoTIFF and NetCDF. I suspect that ISO 19163 will
be very important to Apache SIS when we will start implementing the
org.apache.sis.coverage.grid package.

Other standards worth to note:

  * ISO 19159: Geographic information - Calibration and validation of
    remote sensing imagery sensors and data.
  * ISO 19130: Geographic information - Imagery sensor models for
    geopositioning. This standard is about referencing images taken from
    a platform in air or space.

[14] http://www.isotc211.org/hmmg/HTML/index.htm?goto=1:14:1:4332


      Varia


The meteorological and oceanographic SVG symbols from the World
Meteorological Organisation (WMO) have been incorporated in gvSig. QGIS
will be next.

For meteorological and oceanographic needs, a Web Coverage Service (WCS)
extension is needed: the "DescribeCoverageCollection" operation. It
would make easier to navigate through a large set of data. This
operation can be hierarchical: we may have collections of collections.

The Mobile Location Services group mentioned that a majority of calls to
911 now originate from wireless phones. But the majority of wireless
calls are indoor, and GPS does not give an accurate position when
callers is inside building.

We had a summary of KML 2.3 changes (to be submitted to an OGC vote soon):

  * New geometries: Track (a path over a specified a period of time) and
    MultiTracks
  * New extent: LatLonQuad, which extends the bounding box concept by
    specify the 4 corners of the quadrilateral.

We had a presentation of CDB (Common Database), which is used by flights
simulators. There is a proposal to submit this specification as an OGC
"best practice" document for the simulation community. If I'm
understanding right, this specification is in part a directory structure
convention for finding data needed by flight simulators. The directories
contain images in GeoTIFF or similar open formats, together with
metadata files. In may be of interest to Apache SIS if the directory
structure convention is universal enough for being a good "default
directory structure" that we could offer to users for organizing their data.


    Martin


[ 1] http://www.opengeospatial.org/event/1503tcagenda
[ 2] http://www.geoapi.org/snapshot/index.html
[ 3] http://external.opengeospatial.org/twiki_public/Ideas4OGC/WebHome
[ 4] http://www.w3.org/TR/prov-o/
[ 5] http://sis.apache.org/apidocs/org/apache/sis/metadata/iso/lineage/package-summary.html
[ 6] http://www.w3.org/2015/spatial/charter
[ 7] http://www.w3.org/TR/owl-time/
[ 8] http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=26013
[ 9] http://www.w3.org/2015/spatial/wiki/Main_Page
[10] https://github.com/opengeospatial/ets-19139
[11] http://opengeospatial.github.io/geomatics-geotk/
[12] http://sis.apache.org/apidocs/org/apache/sis/referencing/crs/DefaultCompoundCRS.html
[13] http://www.opengeospatial.org/standards/movingfeatures
[14] http://www.isotc211.org/hmmg/HTML/index.htm?goto=1:14:1:4332
[15] http://www.presagis.com/products_services/products/modeling-simulation/free_tools/cdb_api/

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