IWXXM-3.0-tutorial-metar-LKKV-2007-07-25T12Z
Note that this tutorial has not been updated for IWXXM 3.0
For simplicity, this METAR does not include a trend forecast.
The full XML for this example can be found here.
Note that the XML Namespace is distinct from the schema locations. For reference, these are provided here?.
The <iwxxm:METAR> element encodes a METAR report. status, automatedStation and permissibleUsage are included as XML attributes. In this example, the METAR report contains a single <iwxxm:observation> element. A METAR report may include up to three trend forecasts.
The code fragment below shows the XML Namespace declarations plus the basic structure of this METAR report containing a single observation and zero trend forecasts.
Note that in line 15 of the code fragment the XML attribute gml:id is provided. All instances of this attribute within a given document must be unique. Furthermore, we recommend that the gml:id for the report itself is globally unique, comprising of {report-type}-{aerodrome-identifier}-{issue-time}. The issue time should be provided in ISO 8601 format.
More information regarding the design decisions can be found in the model documentation.
Given the reliance on ISO 19156:2011, the main part of the METAR (e.g. the~ltiwxxm:observation> element) is provided using an instance of <om:OM_Observation>.
The OM_Observation class provides a framework to describe the event of an observation or measurement; estimation of the value (the result) of a property (the observed property) of some entity (the feature of interest) using a specified procedure at a given time. OM_Observation also provides the mechanism to capture quality information about the result and arbitrary parameters concerning the observation event.
OM_Observation allows one to describe arbitrarily complex procedures, from the measurement of air temperature using a particular type of thermometer though to intensive numerical simulations. The process may even facilitate the estimation of values of the properties at some point in the future! To ensure clarity, OM_Observation provides a time at which the procedure completed (the result time) and the time or time-period when the result is relevant (the phenomenon time). For example, a forecast might have a result time of 12:00Z and a phenomenon time of 18:00Z at T+6. Similarly, if one is dealing with physical specimens such as ice-cores, the phenomenon time is the time at which the specimen is collected, whilst the result time may be days, months or even years later when the specimen is tested in the laboratory.
Although omitted in this example, the<iwxxm:trendForecast> element is also provided using an instance of <om:OM_Observation>.
In the conceptual model, the observation types are specified with particular semantics. For example, the METAR observation and trend forecast are characterised by the classes MeteorologicalAerodromeObservation and MeteorologicalAerodromeTrendForecast respectively, both of which are sub-classes of OM_Observation. In the XML document, the category, or class, of observation is specified using the element <om:type>. This provides a reference to a definition of the particular sub-class of OM_Observation. These types are
managed in a controlled register published by WMO at http://codes.wmo.int, e.g.
METAR for Karlovy Vary Airport, 12Z 25 July 2007
This METAR is intended as an example and does not represent actual observed conditions.For simplicity, this METAR does not include a trend forecast.
The full XML for this example can be found here.
XML Namespaces
The following namespaces are used either directly or indirectly in this example:| Description | XML Namespace | Default namespace prefix |
| XML Schema | http://www.w3.org/2001/XMLSchema | xsd |
| XML Linking Language | http://www.w3.org/1999/xlink | xlink |
| OGC GML 3.2.1 http://www.opengis.net/gml/3.2 | ||
| ISO/TS 19139:2007 metadata XML schema implementation | http://www.isotc211.org/2005/gmd | gmd |
| OGC OMXML Observations and Measurements | http://www.opengis.net/om/2.0 | om |
| OGC OMXML Sampling Features | http://www.opengis.net/sampling/2.0 | sf |
| OGC OMXML Spatial Sampling Features | http://www.opengis.net/samplingSpatial/2.0 | sams |
| WMO Observable Property Model(1.2) | http://def.wmo.int/opm/2013 | opm |
| WMO METCE (1.2) | http://def.wmo.int/metce/2013 | metce |
| Aeronautical Information Exchange Model (5.1) | http://www.aixm.aero/schema/5.1.1 | aixm |
| ICAO Meteorological Information Exchange Model (2.1) | http://icao.int/iwxxm/2.1 | iwxxm |
Note that the XML Namespace is distinct from the schema locations. For reference, these are provided here?.
Overview: the METAR report
The XML-encoded METAR has a root element <iwxxm:METAR> within which the XML Namespace information is declared.The <iwxxm:METAR> element encodes a METAR report. status, automatedStation and permissibleUsage are included as XML attributes. In this example, the METAR report contains a single <iwxxm:observation> element. A METAR report may include up to three trend forecasts.
The code fragment below shows the XML Namespace declarations plus the basic structure of this METAR report containing a single observation and zero trend forecasts.
Namespace declarations, basic structure
1 . <?xml version="1.0" encoding="UTF-8"> 2 . <iwxxm:METAR xmlns:iwxxm=";http://icao.int/iwxxm/2.1"; 3 . xmlns:xlink="http://www.w3.org/1999/xlink" 4 . xmlns:gml="http://www.opengis.net/gml/3.2" 5 . xmlns:om="http://www.opengis.net/om/2.0" 6 . xmlns:metce="http://def.wmo.int/metce/2013" 7 . xmlns:aixm="http://www.aixm.aero/schema/5.1.1" 8 . xmlns:sams="http://www.opengis.net/samplingSpatial/2.0" 9 . xmlns:sam="http://www.opengis.net/sampling/2.0" 10 . xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 11 . xsi:schemaLocation="http://icao.int/iwxxm/2.1 12 . http://schemas.wmo.int/iwxxm/2.1/iwxxm.xsd 13 . http://def.wmo.int/metce/2013 14 . http://schemas.wmo.int/metce/1.2/metce.xsd" 15 . gml:id="metar-LKKV-20070725T12Z" 16 . status="NORMAL" 17 . automatedStation="false"> 18 . <iwxxm:observation>...</iwxxm:observation> 19 . </iwxxm:METAR>
Note that in line 15 of the code fragment the XML attribute gml:id is provided. All instances of this attribute within a given document must be unique. Furthermore, we recommend that the gml:id for the report itself is globally unique, comprising of {report-type}-{aerodrome-identifier}-{issue-time}. The issue time should be provided in ISO 8601 format.
Observation structure
WMO METCE and ICAO IWXXM are built on the foundation provided by ISO 19156:2011 "Geographic information — Observations and measurements. As the originator of this ISO standard, the Open Geospatial Consortium also publishes information regarding Observations and Measurement: Topic 20: Observations and Measurements.More information regarding the design decisions can be found in the model documentation.
Given the reliance on ISO 19156:2011, the main part of the METAR (e.g. the~ltiwxxm:observation> element) is provided using an instance of <om:OM_Observation>.
The OM_Observation class provides a framework to describe the event of an observation or measurement; estimation of the value (the result) of a property (the observed property) of some entity (the feature of interest) using a specified procedure at a given time. OM_Observation also provides the mechanism to capture quality information about the result and arbitrary parameters concerning the observation event.
OM_Observation allows one to describe arbitrarily complex procedures, from the measurement of air temperature using a particular type of thermometer though to intensive numerical simulations. The process may even facilitate the estimation of values of the properties at some point in the future! To ensure clarity, OM_Observation provides a time at which the procedure completed (the result time) and the time or time-period when the result is relevant (the phenomenon time). For example, a forecast might have a result time of 12:00Z and a phenomenon time of 18:00Z at T+6. Similarly, if one is dealing with physical specimens such as ice-cores, the phenomenon time is the time at which the specimen is collected, whilst the result time may be days, months or even years later when the specimen is tested in the laboratory.
Although omitted in this example, the<iwxxm:trendForecast> element is also provided using an instance of <om:OM_Observation>.
In the conceptual model, the observation types are specified with particular semantics. For example, the METAR observation and trend forecast are characterised by the classes MeteorologicalAerodromeObservation and MeteorologicalAerodromeTrendForecast respectively, both of which are sub-classes of OM_Observation. In the XML document, the category, or class, of observation is specified using the element <om:type>. This provides a reference to a definition of the particular sub-class of OM_Observation. These types are
managed in a controlled register published by WMO at http://codes.wmo.int, e.g.