Temporal WKT for Calendars SWG

Chair(s):

Heazel, Chuck (WiSC Enterprises)
Hedley, Mark (UK Met Office)

Group Description:

1. Temporal WKT for Calendars SWG


2. Purpose of this Standards Working Group


The purpose of this standards working group is to adapt a set of existing standards to provide the capability to represent and encode temporal metadata within data sets and protocols which uses a customised calendar.


3. Business Value Proposition


The Temporal Domain Working Group has identified a range of communities who use time representations based on calendars which are not the Gregorian calendar as recognised by the International Standards Organisation (ISO) in ISO8601.

In order to provide interoperable representations of this metadata, in data payloads and in standards, extensions to the current metadata standardisation provision are required.

This has particular business value for the Climate Science community, who make extensive use of such temporal representations, and for the wide range of OGC communities who are looking to make use of climate data to interact with their own data sets facilitating further applications.


4. Scope of Work


It is expected that this work will involve extensions to existing OGC standards and ISO standards developed in conjunction with the OGC.

This work programme will deliver:

  • Encodings in ISO 19162 Well Known Text of formal definitions of calendars, ordinals and temporal coordinate reference systems: as an OGC standard, extending ISO19162.
  • Encoding notation for temporal entities (instant, period) with respect to defined calendars, as a new OGC standard.

4.1 Statement of relationship of planned work to the current OGC standards baseline

The ISO and OGC standards which influence this domain and may require updating:

  • ISO 8601 - Data elements and interchange formats - Information interchange - Representation of dates and times
  • ISO 19108 - Geographic information - Temporal schema
  • ISO 19111 - Geographic information - Spatial referencing by coordinates
  • ISO 19162 - Well Known Text for Coordinate Reference systems
  • OGC 13-102r2 Name type specification - Time and index coordinate reference system definitions

4.2 What is Out of Scope?

Conversion between date-times in different calendars is out of scope.

4.3 Specific Contribution of Existing Work as a Starting Point

The work of the CRS-WKT SWG provides an encoding framework, in ISO19162, linked to other ISO standards, to handle a set of requirements for Gregorian calendar based temporal metadata.

ISO8601 provides a notation for encoding times with respect to the gregorian calendar.

4.4 Determination of SWG Completion

The SWG work will be complete when the use cases adopted by the SWG Charter are able to be delivered against using adopted standards.

4.5 Is this a persistent SWG?

X Yes No

4.6 When can SWG be inactivated or rechartered?

Following SWG completion, all information is archived, all proposals adopted and the updated standards available for use by the community.


5. Description of Deliverables


5.1 Definition of a Calendar

  • ISO 19108 provides a framework for defining a calendar from basic building blocks.
  • Defining the gregorian calendar, including leap years and leap seconds is hard. This is not required as ISO8601 mandates that all 8601 definitions are with respect to the gregorian calendar.
  • Defining a no leap second gregorian calendar will be required, as many software implementations handle standard time this way.
  • Simplified geophysical model calendars are easier to define, with regular periodicity and lacking corrections.

5.2 Definition of an Instant in Time

  • A syntax for defining an instant in time, with respect to a calendar is required.
  • This enables a zero point to be defined and calculations using offsets from that origin to be undertaken.

5.3 Definition of a Customised Temporal Coordinate Reference System

  • A temporal coordinate reference system provides the context to comprehend a numerical temporal coordinate.
  • It consists of:
    • a calendar definition;
    • a time origin (sometimes the term epoch is used)
    • a unit of measure

5.4 Encoding of a Customised Temporal CRS in Well Known Text

  • ISO 19162 provides the Well Known Text syntax for encoding a TCRS.
  • It is currently limited to working with the ISO Gregorian calendar
  • We need to be able to define a calendar instance:
    • Do we need syntax to explicitly define the calendar instance in WKT?
    • Can we depend only on some system of external referencing?

5.5 Definition of a time period

  • A time period shall have a duration, able to be defined in SI units.
  • A time period is defined with respect to a well defined calendar.
  • A time period may be specified as a bounded quantity between two well defined instants in time:
    • 2015-06-02:21:20:000 | 2015-06-02:21:30:000
  • A time period may be defined the entire duration of a well defined temporal quantity:
    • 2012-06
  • A time period may be defined by the intersection of a set of independent temporal quantities:
    • 1979 | 2010 ; December | February
  • A partial time period may be defined by either the start or the end, with the other unknown.

IPR Policy for this SWG


x RAND-Royalty Free.


7. Other Informative Remarks about this SWG


a. Similar or Applicable Standards Work (OGC and Elsewhere)

The following standards and projects may be relevant to the SWG's planned work, although none currently provide the functionality anticipated by this committee's deliverables:

  • ISO 8601 - Data elements and interchange formats - Information interchange - Representation of dates and times
  • ISO 19108 - Geographic information - Temporal schema
  • ISO 19111 - Geographic information - Spatial referencing by coordinates
  • ISO 19162 - Well Known Text for Coordinate Reference systems
  • OGC 13-102r2 Name type specification - Time and index coordinate reference system definitions
  • The SWG intends to seek and if possible maintain liaison with each of the organizations maintaining the above works.

b. Details of the First Meeting

The first meeting of the SWG will be held by telephone conference call at a time to be confirmed. Call-in information will be provided to the SWG's e-mail list and on the portal calendar in advance of the meeting.

c. Projected On-going Meeting Schedule

The work of the SWG will be carried out primarily by email and conference calls, possibly every four weeks, with face-to-face meetings perhaps at each of the OGC TC meetings.

d. Supporters of the Proposal (Charter Members)

The following people support this proposal and are committed to the Charter and projected meeting schedule. These members are known as SWG Founding or Charter members. The charter members agree to the SoW and IPR terms as defined in this charter. The charter members have voting rights beginning the day the SWG is officially formed. Charter Members are shown on the public SWG page. Extend the table as necessary.

NameOrganization
Mark Hedley Met Office
Charles Heazel WiSC Enterprises
Robert Gibb Landcare Research New Zealand

e. Convener(s)

Mark Hedley, Met Office
Charles Heazel, WiSC Enterprises