IWXXM-3.0-tutorial-va-sigmet-EGXX-YYYY-MM-25T16Z
Note that this tutorial has not been updated for IWXXM 3.0
This VA SIGMET is intended as an example and does not represent actual conditions.
The year and month of the issue of this VA SIGMET
are unknown; these have been substituted with YYYY and MM respectively.
This tutorial is intended as a follow-on from the simple METAR tutorial.
Please work through the METAR example first as this VA SIGMET tutorial assumes that many of the key points will already be understood.
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 code fragment below illustrates the report structure:
The VA SIGMET report comprises:
The code fragment below illustrates the outline structure of the <<m:OM_Observation> instance:
The analysis <om:OM_Observation> follows the standard OM_Observation pattern:
As outlined in the METAR example, the procedure is constrained such that is must be an instance of METCE Process. As described therein, <gml:description> is used to cite a well-known reference - in this case the appropriate clause from the ICAO Annex 3 (WMO No. 49 Vol 2) technical regulations.
The feature of interest for the SIGMET analysis is intended to describe the Flight Information Region associated with the SIGMET report. As such, the feature of interest is constrained such that it must be an instance of SF_SamplingSurface and thus follows the standard pattern for all SF_SpatialSamplingFeatures:
The analysis result provides one up to two observed position and motion characteristics of the volcanic ash clouds. In order to align with timings for Volcanic Ash Advisory (VAA) products, the SIGMET analysis may describe the characteristics of the volcanic ash clouds at some point in the near future (e.g. up to 2-hours hence); e.g. a forecast of the volcanic ash clouds characteristics.
The result is constrained such that it must be an instance of SIGMETEvolvingConditionCollection. This class has been specifically designed to meet the requirements published in ICAO Annex 3 (WMO No. 49 Vol 2) regulation and allows one to specify a collection of
meteorological features (e.g. the volcanic ash cloud or other significant weather phenomena) described by one or more members each of which contain an
instance of SIGMETEvolvingCondition.
The code fragment above illustrates the encoding of <iwxxm:SIGMETEvolvingConditionCollection> and <iwxxm:SIGMETEvolvingCondition>:
The forecast result provides one up to two predicted positions of the volcanic ash clouds.
The result is constrained such that it must be an instance of SIGMETPositionCollection (from IWXXM). This class comprises one or more members, each of which must be of type SIGMETPosition (from IWXXM). Once again, these classes have been specifically designed to meet the requirements published in ICAO Annex 3 / WMO No. 49 Volume 2 regulation.
The code fragment above illustrates the encoding of <iwxxm:MeteorologicalPositionCollection>:
The final element of the VA SIGMET report is provision of information about the source of the volcanic ash; the name and position of the erupting volcano. The code fragment above illustrates:
This VA SIGMET is intended as an example and does not represent actual conditions.
The year and month of the issue of this VA SIGMET
are unknown; these have been substituted with YYYY and MM respectively.
This tutorial is intended as a follow-on from the simple METAR tutorial.
Please work through the METAR example first as this VA SIGMET tutorial assumes that many of the key points will already be understood.
The full XML for this example can be found here.
TAC-encoding
This example is based on the following VA SIGMET:EGGX SIGMET 4 VALID 251600/252200 EGRR – EGGX SHANWICK OCEANIC FIR VA ERUPTION MT HEKLA PSN N6359 W01940 VA CLD OBS AT 1600Z SFC/FL550 N6000 W01150 - N5900 W01300 - N6000 W01600 - N6000 W01150 MOV S 60KT NC FCST 2200Z SFC/FL550 N6000 W01200 - N5800 W01400 - N6000 W01535 - N6000 W01200=
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 | gml |
| 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 |
| 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 VA SIGMET <report:VolcanicAshSIGMET> within which the XML Namespace information is declared.
The VA SIGMET report is comprised of:- report metadata (e.g. status, issuing centre, originating meteorological watch office etc.);
- one analysis providing one up to two observed or forecast position and motion of the volcanic ash cloud;
- one forecast providing one up to two predicted positions of the volcanic ash cloud.
- if there are more than one observed and/or predicted positions of volcanic ash clouds, it is expected that the first predicted position corresponds to the first observed position and so forth.
The code fragment below illustrates the report structure:
1 . ~lt~?xml version="1.0" encoding="UTF-8"> 2 . <iwxxm:VolcanicAshSIGMET xmlns:iwxxm="http://icao.int/iwxxm/2.1" 3 . xmlns:aixm="http://www.aixm.aero/schema/5.1.1" 4 . xmlns:metce="http://def.wmo.int/metce/2013" 5 . xmlns:om="http://www.opengis.net/om/2.0" 6 . xmlns:sam="http://www.opengis.net/sampling/2.0" 7 . xmlns:sams="http://www.opengis.net/samplingSpatial/2.0" 8 . xmlns:gml="http://www.opengis.net/gml/3.2" 9 . xmlns:xlink="http://www.w3.org/1999/xlink" 10 . xmlns:xsd="http://www.w3.org/2001/XMLSchema" 11 . xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 12 . xsi:schemaLocation="http://icao.int/iwxxm/2.1 http://schemas.wmo.int/iwxxm/2.1/iwxxm.xsd 13 . http://def.wmo.int/metce/2013 http://schemas.wmo.int/metce/1.2/metce.xsd" 14 . gml:id="va-sigmet-EGXX-YYYYMM25T160000Z" 15 . permissibleUsage="OPERATIONAL" 16 . status="NORMAL"~gt~ 17 . <iwxxm:issuingAirTrafficServicesUnit>...</iwxxm:issuingAirTrafficServicesUnit> 18 . <iwxxm:originatingMeteorologicalWatchOffice>...</iwxxm:originatingMeteorologicalWatchOffice> 19 . <iwxxm:sequenceNumber>4</iwxxm:sequenceNumber> 20 . <iwxxm:validPeriod>...</iwxxm:validPeriod> 21 . <iwxxm:phenomenon xlink:href="http://codes.wmo.int/49-2/SigWxPhenomena/VA" xlink:title="Volcanic Ash"/> 22 . <iwxxm:analysis>...</iwxxm:analysis> 23 . <iwxxm:forecastPositionAnalysis>...~lt/iwxxm:forecastPositionAnalysis> 24 . <iwxxm:eruptingVolcano>...</iwxxm:eruptingVolcano> 25 . </iwxxm:VolcanicAshSIGMET>
The VA SIGMET report comprises:
- (Line 14) a unique identifier for the report (e.g. "va-sigmet-EGXX-YYYYMM25T160000Z"); each VA SIGMET report should have a unique identifier of the form: va-sigmet-{issuing Air Traffic Service Unit}-{issue date-time}.
- (Line 15) permissible usage; in this case operational
- (Line 16) report status; in this case normal
- (Line 17) information about the issuing Air Traffic Services Unit (elaborated below)
- (Line 18) information about the originating Meteorological Watch Office (elaborated below)
- (Line 19) report sequence number - following the standard ICAO Annex 3 (WMO No. 49 Vol 2) rules for report assigning sequence numbers
- (Line 20) definition of the validity period for this report (elaborated below)
- (Line 21) definition of the significant weather phenomenon that the report describes; in this case Volcanic Ash. Terms are referenced using xlink:href from the WMO Codes Register http://codes.wmo.int/49-2/SigWxPhenomena. xlink:title is provided to supplement human readability.
- (Line 22) the analysis provides one up to two observed or forecast positions and motions of the volcanic ash clouds. This is encoded as an instance of <om:OM_Observation> (elaborated below).
- (Line 23) the forecast provides one up to two predicted positions of the volcanic ash clouds. This is encoded as an instance of <om:OM_Observation> (elaborated below).
- (Line 24) provides information about the source of the volcanic ash; the name and position of the erupting volcano (elaborated below).
Issuing Air Traffic Services Unit and Originating Meteorological Watch Office
<iwxxm:issuingAirTrafficServicesUnit>
<aixm:Unit gml:id="fic-EGGX">
<aixm:timeSlice>
<aixm:UnitTimeSlice gml:id="fic-EGGX-ts">
<gml:validTime/>
<aixm:interpretation>SNAPSHOT</aixm:interpretation>
<aixm:name>SHANWICK OCEANIC AREA CONTROL CENTRE</aixm:name>
<aixm:type>ATCC</aixm:type>
<aixm:designator>EGGX</aixm:designator>
</aixm:UnitTimeSlice>
</aixm:timeSlice>
</aixm:Unit>
</iwxxm:issuingAirTrafficServicesUnit>
<iwxxm:originatingMeteorologicalWatchOffice>
<aixm:Unit gml:id="wmo-EGRR">
<aixm:timeSlice>
<aixm:UnitTimeSlice gml:id="mwo-EGRR-ts">
<gml:validTime/>
<aixm:interpretation>SNAPSHOT</aixm:interpretation>
<aixm:name>UK METEOROLOGICAL OFFICE - EXETER</aixm:name>
<aixm:type>MWO</aixm:type>
<aixm:designator>EGRR</aixm:designator>
</aixm:UnitTimeSlice>
</aixm:timeSlice>
</aixm:Unit>
</iwxxm:originatingMeteorologicalWatchOffice>
...- Information about both Issuing Air Traffic Services Unit (ATSU) and Originating Meteorological Watch Office (MWO) is included in the SIGMET report. Both of these entities conform to the Unit data model defined in the Aeronautical Information eXchange Model (AIXM). This is intended to align with the broader ICAO Aeronautical Information Reference Model (AIRM); albeit only a subset of the information required for meteorological products is required.
- The gml:ids shown here are fictitious. A core feature enabling consistency and alignment within the AIRM, is the use of UUIDs (http://www.ietf.org/rfc/rfc4122.txt|RFC 4122]) for identifying and referencing information about aeronautical features. The use of UUIDs is adopted from AIXM 5, conjointly developed by EuroControl and US FAA. A managed set of information describing an aeronautical feature is allocated a UUID by the data publisher. The UUID is an opaque identifier and may be automatically generated (e.g. using an online UUID-generator or other mechanism). Once assigned by a data publisher, the UUID may be used as a unique reference to the given set of information, thus enabling distributed systems to assert that they are, indeed, using consistent information.
- Additional information provided about the ATSU and MWO includes:
- name: this must be provided in BLOCK CAPITALS
- type: one of the following options - ARO (Aerodrome Reporting Office/ATS Reporting Office), ATCC (Air Traffic Control Centre), ATSU (Air Traffic Services Unit), FIC (Flight Information Centre) or MWO (Meteorological Watch Office)
- designator: the coded designator associated with the Unit - this may be the ICAO 4-letter Location Indicator as specified in ICAO Doc 7910.
Valid period
... <iwxxm:validPeriod> <gml:TimePeriod gml:id="tp-25T16Z-25T22Z"> <gml:beginPosition>YYYY-MM-25T16:00:00Z</gml:beginPosition> <gml:endPosition>YYYY-MM-25T22:00:00Z</gml:endPosition> </gml:TimePeriod> </iwxxm:validPeriod> ...
- <iwxxm:validPeriod> defines the period during which this SIGMET is valid; noting the use of YYYY and MM in place of year and month - normally these would be populated (e.g. 2013-05-08T15:58:00Z)
- The <om:OM_Observation> instances for the analysis and forecast both include the element <om:validTime> which has identical semantics to <iwxxm:validPeriod>.
- Even though information is logically repeated, <iwxxm:validPeriod> has been retained to make it easier to map the XML encoding onto the ICAO Annex 3 regulation.
SIGMET Analysis
The analysis provides one up to two observed or forecast positions and motions of the volcanic ash clouds. This is encoded as an instance of <om:OM_Observation>.The code fragment below illustrates the outline structure of the <<m:OM_Observation> instance:
1 . ... 2 . <iwxxm:analysis> 3 . <om:OM_Observation gml:id="va-position-and-motion-EGXX-YYYYMM25T16Z"> 4 . <om:type xlink:href="http://codes.wmo.int/49-2/observation-type/IWXXM/2.1/SIGMETEvolvingConditionAnalysis"/> 5 . <om:phenomenonTime> 6 . <gml:TimeInstant gml:id="ti-25T16Z"> 7 . <gml:timePosition>YYYY-MM-25T16:00:00Z</gml:timePosition> 8 . </gml:TimeInstant> 9 . </om:phenomenonTime> 10 . <om:resultTime xlink:href="#ti-25T16Z"/> 11 . <om:validTime xlink:href="#tp-25T16Z-25T22Z"/> 12 . <om:procedure>...</om:procedure> 13 . <om:observedProperty 14 . xlink:href="http://codes.wmo.int/49-2/SigWxPhenomena/VA" 15 . xlink:title="Volcanic ash"/> 16 . <om:featureOfInterest>...</om:featureOfInterest> 17 . <om:result>...</om:result> 18 . </om:OM_Observation> 19 . </iwxxm:analysis> 20 . ...
The analysis <om:OM_Observation> follows the standard OM_Observation pattern:
- (Line 3) the <om:OM_Observation> instance is allocated a unique identifier within the scope of the XML document (e.g. "va-position-and-motion-EGXX-YYYYMM25T16Z"); there are no special rules applied here with regards to the structure of the identifier. The only requirements are that it is unique within the document.
- (Line 4) as outlined in the METAR tutorial, the observation type is specified via reference to a definition published within the WMO Codes Registry. For SIGMET "analysis" this is SIGMETEvolvingConditionAnalysis
- (Lines 5-9) the phenomenon time indicates the time-instant associated with the given position and motion of the volcanic ash cloud described in the result below. In this example, the observed position and motion of the ash cloud is provided, thus the phenomenonTime is commensurate with the beginning of the SIGMET report validity period. The phenomenon time is expressed in ISO 8601 format: "YYYY-MM-25T16:00:00Z" (noting that YYYY and MM would normally specify year and month respectively).
- (Line 10) the result time indicates the time-instance at which the information about the position and motion of the volcanic ash cloud was made available. This always commensurate with the beginning of the SIGMET report validity period. In this case, this is the same time-instant that was used to describe the phenomenon time thus xlink:href is used to refer to the earlier definition.
- (Line 11) the valid time indicates the time-period for which the information about the position and motion of the volcanic ash cloud is valid - in this case according to international regulation. This is identical to the valid period defined in the body of the SIGMET report, thus xlink:href is used to refer
- (Line 12) the procedure by which the position and motion of the volcanic ash cloud was observed (elaborated below).
- (Lines 13-15) the observed property identifies the physical phenomenon being observed. Following consideration, it seems appropriate to reference "volcanic ash" as the observed property, rather than an aggregate of "position and motion" about some undefined significant weather phenomena! The observed property is used a key when searching for content within a service conforming to the Open Geospatial Consortium's Sensor Observation Service (SOS) specification; it seems likely that consumers of the data product will search based on the type of significant weather phenomena rather than the characteristics of that phenomenon. Given that observed property must be a reference (e.g. specified using xlink:href), we reference a term from the WMO Codes Registry (e.g. http://codes.wmo.int/49-2/SigWxPhenomena/VA"). xlink:title provides a supplemental human-readable description.
- (Line 16) the feature of interest provides information about the real world feature that the observation pertains to - in this case a Flight Information Region (elaborated below).
- (Line 17) the result provides the information about the observed characteristics of the volcanic ash cloud (elaborated below).
SIGMET Analysis:
Procedure1 . ... 2 . <om:procedure> 3 . <metce:Process gml:id="p-49-2-va-sigmet"> 4 . <gml:description>WMO No. 49 Volume 2 Meteorological Service for International Air Navigation 5 . [C.3.1.]7 SIGMET AND AIRMET INFORMATION, AERODROME WARNINGS AND WIND SHEAR 6 . WARNINGS AND ALERTS 7 . </gml:description> 8 . </metce:Process> 9 . </om:procedure> 10 . ...
As outlined in the METAR example, the procedure is constrained such that is must be an instance of METCE Process. As described therein, <gml:description> is used to cite a well-known reference - in this case the appropriate clause from the ICAO Annex 3 (WMO No. 49 Vol 2) technical regulations.
SIGMET Analysis: Feature of interest
1 . ... 2 . <om:featureOfInterest> 3 . <sams:SF_SpatialSamplingFeature gml:id="ss-SHANWICK_OCA"> 4 . <sam:type xlink:href="http://www.opengis.net/def/samplingFeatureType/OGC-OM/2.0/SF_SamplingSurface"/> 5 . <sam:sampledFeature> 6 . <aixm:Airspace gml:id="fir-EGGX"> 7 . <aixm:timeSlice> 8 . <aixm:AirspaceTimeSlice gml:id="fir-EGGX-ts"> 9 . <gml:validtime/> 10 . <aixm:interpretation>SNAPSHOT</aixm:interpretation> 11 . <aixm:type>FIR</aixm:type> 12 . <aixm:designator>EGXX</aixm:designator> 13 . <aixm:name>SHANWICK OCEANIC FIR</aixm:name> 14 . </aixm:AirspaceTimeSlice> 15 . </aixm:timeSlice> 16 . </aixm:Airspace> 17 . </sam:sampledFeature> 18 . <!-- FIR boundary - not typically reported --> 19 . <sams:shape nilReason="withheld"/> 20 . </sams:SF_SpatialSamplingFeature> 21 . </om:featureOfInterest> 22 . ...
The feature of interest for the SIGMET analysis is intended to describe the Flight Information Region associated with the SIGMET report. As such, the feature of interest is constrained such that it must be an instance of SF_SamplingSurface and thus follows the standard pattern for all SF_SpatialSamplingFeatures:
- (Line 3) the <sams:SF_SpatialSamplingFeature> instance is allocated a unique identifier within the scope of the XML document (e.g. "ss-SHANWICK_OCA"); there are no special rules applied here with regards to the structure of the identifier. The only requirements are that it is unique within the document.
- (Line 4) the type of the <sams:SF_SpatialSamplingFeature> instance; in this case a SF_SamplingSurface.
- (Lines 5-17) the sampled feature describes the real world feature to which the observation pertains; in this case the Shanwick Oceanic Flight Information Region.
- (Lines 6-16) in lieu of an authoritative web-accessible register of information about Flight Information Regions, the information about Shanwick Oceanic FIR must be embedded within the SIGMET report. The data model used to describe the FIR is Airspace from the Aeronautical Information eXchange Model (AIXM). This is intended to align with the broader ICAO Aeronautical Information Reference Model (AIRM); albeit only a subset of the information required for meteorological products is required. While the gml:id shown here is fictitious, a core feature enabling consistency and alignment within the AIRM, is the use of UUIDs (RFC 4122) as outlined above (ATSU and MWO) - see line 6. Additional information provided about the Airspace includes:
- (Line 11) type: one of FIR (Flight Information Region), UIR (Upper flight Information Region) or CTA (Control Area)
- (Line 12) designator: a coded designator associated with the Airspace - in this case the ICAO location indicator "EGXX"
- (Line 13) name: the textual name allocated to the Airspace by the responsible authority - this must be provided in BLOCK CAPITALS
- (Line 18) The FIR bounding is not typically reported.
SIGMET Analysis Result
1 . ... 2 . <om:result> 3 . <iwxxm:SIGMETEvolvingConditionCollection gml:id="emc-va-obs-EGXX-YYYYMM25T16Z" timeIndicator="OBSERVATION"> 4 . <iwxxm:member> 5 . <iwxxm:SIGMETEvolvingCondition gml:id="sec1" intensityChange="NO_CHANGE"> 6 . <iwxxm:directionOfMotion uom="deg">180</iwxxm:directionOfMotion> 7 . <iwxxm:geometry> 8 . <aixm:AirspaceVolume gml:id="av-va-obs-position-EGGX-YYYYMM25T16Z"> 9 . <!-- omitted lower-limit implies that the volcanic ash cloud extends to ground/sea surface --> 10 . <aixm:upperLimit uom="FL">550</aixm:upperLimit> 11 . <aixm:upperLimitReference>STD</aixm:upperLimitReference> 12 . <aixm:horizontalProjection> 13 . <aixm:Surface gml:id="polygon-va-obs-position-EGGX-YYYYMM25T16Z" 14 . uomLabels="deg deg" 15 . axisLabels="Lat Lon" 16 . srsDimension="2" 17 . srsName="http://www.opengis.net/def/crs/EPSG/0/4326"> 18 . <gml:polygonPatches> 19 . <gml:PolygonPatch> 20 . <gml:exterior> 21 . <gml:LinearRing> 22 . <!-- bounding polygon clipped to edge of FIR @ 60N --> 23 . <gml:posList> 24 . 60.0 -11.5 25 . 59.0 -13.0 26 . 60.0 -16.0 27 . 60.0 -11.5 28 . </gml:posList> 29 . </gml:LinearRing> 30 . </gml:exterior> 31 . </gml:PolygonPatch> 32 . </gml:polygonPatches> 33 . </aixm:Surface> 34 . </aixm:horizontalProjection> 35 . </aixm:AirspaceVolume> 36 . </iwxxm:geometry> 37 . <iwxxm:speedOfMotion uom="[kn_i]">60</iwxxm:speedOfMotion> 38 . </iwxxm:SIGMETEvolvingCondition> 39 . </iwxxm:member> 40 . </iwxxm:SIGMETEvolvingConditionCollection> 41 . </om:result> 42 . ...
The analysis result provides one up to two observed position and motion characteristics of the volcanic ash clouds. In order to align with timings for Volcanic Ash Advisory (VAA) products, the SIGMET analysis may describe the characteristics of the volcanic ash clouds at some point in the near future (e.g. up to 2-hours hence); e.g. a forecast of the volcanic ash clouds characteristics.
The result is constrained such that it must be an instance of SIGMETEvolvingConditionCollection. This class has been specifically designed to meet the requirements published in ICAO Annex 3 (WMO No. 49 Vol 2) regulation and allows one to specify a collection of
meteorological features (e.g. the volcanic ash cloud or other significant weather phenomena) described by one or more members each of which contain an
instance of SIGMETEvolvingCondition.
The code fragment above illustrates the encoding of <iwxxm:SIGMETEvolvingConditionCollection> and <iwxxm:SIGMETEvolvingCondition>:
- (Line 3) an XML atribute timeIndicator in <iwxxm:SIGMETEvolvingConditionCollection> identifies whether this section refers to an "OBSERVATION" or "FORECAST"
- (Line 4) the instance of <iwxxm:SIGMETEvolvingConditionCollection> contains <iwxxm:member> each of which has an instance of <iwxxm:SIGMETEvolvingCondition>
- (Line 5) the instance of <iwxxm:SIGMETEvolvingCondition> is uniquely identified within the scope of the XML document. Additionally, we see the intensity change specified as an XML attribute. In this case the value is "NO_CHANGE". The permitted set of options also includes "WEAKEN" and "INTENSIFY" as per the ICAO Annex 3 (WMO No. 49 Vol 2) technical regulation.
- (Line 6) specifies the direction of motion of the volcanic ash cloud specified in degrees from true-north; in this case the value is 180 degrees (e.g. due south).
- (Lines 7-36) specifies a 2.5-dimensional representation of the observed geometry of the volcanic ash cloud using an instance of <iwxxm:AirspaceVolume>. In this case, the horizontal projection is given (lines 12-34) along with the upper limit at FL550 (line 10); the omitted lower limit implies that surface. Note that the upper-limit height is specified as measured in the ICAO standard atmosphere "STD" thus allowing for assessment of altitude as a linear distance when reading converting from barometric pressure (line 11). The horizontal projection is provided as an instance
- (Line 37) specifies the speed of motion of the volcanic ash cloud; in this case a velocity of 60 knots.
SIGMET Forecast: Result
1 . ... 2 . <om:result> 3 . <iwxxm:SIGMETPositionCollection gml:id="mpc-EGGX-YYYYMM25T16Z"> 4 . <iwxxm:member> 5 . <iwxxm:SIGMETPosition gml:id="mp-va-fcst-EGGX-YYYYMM25T16Z"> 6 . <iwxxm:geometry> 7 . <aixm:AirspaceVolume gml:id="av-va-fcst-position-EGGX-YYYYMM25T22Z"> 8 . <aixm:horizontalProjection> 9 . <aixm:Surface gml:id="polygon-va-fcst-position-EGGX-YYYYMM25T22Z" 10 . uomLabels="deg deg" 11 . axisLabels="Lat Lon" 12 . srsDimension="2" 13 . srsName="http://www.opengis.net/def/crs/EPSG/0/4326"> 14 . <gml:polygonPatches> 15 . <gml:PolygonPatch> 16 . <gml:exterior> 17 . <gml:LinearRing> 18 . <!-- bounding polygon clipped to edge of FIR @ 60N --> 19 . <gml:posList> 20 . 60.0 -12.0 21 . 58.0 -14.0 22 . 60.0 -15.35 23 . 60.0 -12.0 24 . </gml:posList> 25 . </gml:LinearRing> 26 . </gml:exterior> 27 . </gml:PolygonPatch> 28 . </gml:polygonPatches> 29 . </aixm:Surface> 30 . </aixm:horizontalProjection> 31 . </aixm:AirspaceVolume> 32 . </iwxxm:geometry> 33 . </iwxxm:SIGMETPosition> 34 . </iwxxm:member> 35 . </iwxxm:SIGMETPositionCollection> 36 . </om:result> 37 . ...
The forecast result provides one up to two predicted positions of the volcanic ash clouds.
The result is constrained such that it must be an instance of SIGMETPositionCollection (from IWXXM). This class comprises one or more members, each of which must be of type SIGMETPosition (from IWXXM). Once again, these classes have been specifically designed to meet the requirements published in ICAO Annex 3 / WMO No. 49 Volume 2 regulation.
The code fragment above illustrates the encoding of <iwxxm:MeteorologicalPositionCollection>:
- (Lines 3-35) define the collection - on this occasion with just a single member (e.g. only one position is predicted for the volcanic ash cloud at T+6hrs).
- (Lines 5-33) define the position of the volcanic ash cloud at 22:00Z. The SIGMET"forecast" only requires the geometry of the volcanic ash cloud to be provided - once more via an instance of <aixm:AirspaceVolume> (lines 7-31).
Erupting volcano
1 . ... 2 . <iwxxm:eruptingVolcano> 3 . <metce:Volcano gml:id="v-MT-HEKLA"> 4 . <metce:name>MT HEKLA</metce:name> 5 . <metce:position> 6 . <gml:Point gml:id="ref-point-MT-HEKLA" 7 . uomLabels="deg deg" 8 . axisLabels="Lat Lon" 9 . srsDimension="2" 10 . srsName="http://www.opengis.net/def/crs/EPSG/0/4326"> 11 . <gml:pos>63.59 -19.40</gml:pos> 12 . </gml:Point> 13 . </metce:position> 14 . </metce:Volcano> 15 . </iwxxm:eruptingVolcano> 16 . ...
The final element of the VA SIGMET report is provision of information about the source of the volcanic ash; the name and position of the erupting volcano. The code fragment above illustrates:
- (Line 3) erupting volcano: a uniquely identified instance of <metce:Volcano>. METCE also provides a EruptingVolcano class which the provision for stating the date of the volcanic eruption if known. However, there is no requirement to provide this information within the VA SIGMET.
- (Line 4) volcano name. Note that the "Global Volcanism Program" provides an online, searchable catalogue of volcanoes which may assist in identifying the authoritative name for a given volcano feature.
- (Lines 5-13) position specifies the geographic location of the volcano using an instance of <gml:Point>.