IWXXM-2

IWXXM v2
This page is the entry point for documentation of WMO IWXXM v2.
IWXXM v2 supports the exchange of meteorological information in XML, including support of international civil aviation under the regulations provided by ICAO Annex 3 and WMO-No. 49 Volume II as updated by Amendment 77-A.

IWXXM v2 is expected to be issued in two sub-versions. The first (v2.0) had been presented to the sixteenth session of the WMO Commission for Basic Systems and a decision had been made on preliminary operational use. The version finally adopted by the WMO Executive Council in June 2017 was IWXXM 2.1.

Sub-release IWXXM 2.1.1 has been approved for implementation on 15 May 2018 using the fast track procedure as amendment MM51. This corrects issues with validation that cause some correct messages to be flagged as invalid using schematron validation. Centres validating messages may wish to use the schematron in IWXXM 2.1.1 in a pre-operational state in order to avoid this issue.

Operational use of IWXXM 2.1

Information exchange using AMHS

  • ICAO practice is that all IWXXM documents exchanged using the ICAO AMHS system must be part of a COLLECT collection.

Content of COLLECT documents

  • Insert component documents into a COLLECT document without change. The intention of the COLLECT schema is to allow several reports that are expressed as iwxxm documents to be exchanged as a single document for communications and storage purposes. Users will need to extract the component documents from the COLLECT document. Inserting the iwxxm documents into COLLECT without change makes this extraction easier. In particular, the namespace definitions should remain within the component iwxxm documents and should *not* be rationalized into a single set of definitions.

Use of gml:id

  • IWXXM requires the gml:id elements within a document to be distinct. Although the guidance associated with iwxxm 2.1 suggests ways this can be achieved within a single document, experience with using iwxxm has shown that the guidance would allow the same values of gml:id could be created for different documents; this causes problems for centres creating COLLECT documents because it can result in duplicate gml:id elements. Using Universally Unique IDentifiers (uuids) would solve this problem. Recommended practice is to use a UUIDv4 identifier based on a random number (the same as is recommended for AIXM) and to specify a codeSpace: 
<om:phenomenonTime>
     <gml:TimeInstant gml:id="uuid.a82b3fc9-4aa4-4e67-8def-aaea1ac595j">
        <gml:identifier codeSpace="urn:uuid:"><a82b3fc9-4aa4-4e67-8defaaea1ac595j>
        </gml:identifier>
     ...

Structure of IWXXM

IWXXM is built on several packages.

Packages managed by WMO

METCE- 'Modele pour l'Echange des informations sur le Temps, le Climat et l'Eau' (METCE) - a set of foundation building blocks to support application schema in the domains of interest to WMO, notably the weather, climate, hydrology, oceanography and space weather disciplines.
Observable Property Model (OPM) - based on work by the OGC Sensor Working Group, this allows creation of definitions that are derived from the meteorological basic types.
Feature Collection Model (COLLECT) - used to represent a collection of GML feature instances of the same type of meteorological information.

Packages managed for ICAO

IWXXM - ICAO Meteorological Information Exchange Model - defines the reports required by ICAO (the equivalent of METAR/SPECI, TAF, SIGMET, AIRMET, Tropical Cyclone Advisory (TCA) and Volcanic Ash Advisory (VAA)) that are built with WMO packages.

More details of these packages are available from the wiki page IWXXM-2-Packages.

Release package for IWXXM v2

The draft version of packages including IWXXM 2.1 and METCE 1.2 are now available. The packages and related information are IWXXM-2-Release linked from the Release Package wiki page. This includes links to the schemas.

Registry to support IWXXM

A web accessible registry (codes.wmo.int) contains information about the supplemental resource required to publish data products in the IWXXM format, such as code lists.

Further information about the WMO Codes Registry can be found on the "About" page of codes.wmo.int.

Validation of IWXXM Reports

The correct formatting of IWXXM messages is comprised of two parts: (1) validation against the IWXXM XML schemas and (2) validation against rules written in ISO Schematron. The IWXXM XML Schema and Schematron rules jointly describe how IWXXM messages should be formatted. XML schema and Schematron are standardized technology, and therefore a number of open source and closed source software packages can be used for validation.

A command line tool is provided by WMO for authoritative validation purposes. CRUX is a cross-platform Java tool which supports validating IWXXM XML schemas and Schematron rules, and is available at https://github.com/NCAR/crux/releases.

For offline and/or local validation purposes, Crux can be used with an XML catalog file to utilize local copies of XML schema and Schematron rules. For convenience, a schema bundle is distributed for use with Crux or other XML validation tools.

An authoritative validation website for WMO and ICAO data models is available at http://wmo-icao-validator.rap.ucar.edu. Based on Crux, schemas which are hosted from schemas.wmo.int can be validated there, including IWXXM, METCE, WMO Collect, and others. The site uses local copies of XML Schema and Schematron files. XML files with WMO, ICAO, ISO, and OGC namespaces should validate quickly without any outgoing network connections.

Release notes for IWXXM v2

Release notes for IWXXM 2 are included in the release Package. They are available from the Release Notes wiki page.

Tutorial for IWXXM v2

Tutorials on IWXXM are available.

Reference materials

  1. Manual on Codes (WMO No. 306) Volume I.3
  2. Tables A and B7 of the Manual on the Global Telecommunication System (WMO No. 386)

Index to supporting pages

The structure of the pages within the wiki that support this consultation is shown below.

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