5.3.2 O&M

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Contents

Overview

The Observation and Measurements (O&M) specification provides a standard model for representing and exchanging observation results. O&M is primarily a conceptual model describing the relationship between different aspects of the data-capture process to one another. According to O&M an observation is an event which occurs at a certain point in time and that generates a value for the observed phenomenon. Besides the time and value of a measurement, O&M is capable of describing other measurement properties, e.g. the process used to generate the measurement value as well as the location and quality of the measurement. O&M considers a measurement value to be an approximation of an attribute of the observed feature of interest (FOI), additional information is regarded as metadata for further analysis and interpretation of the data. Thus, an observation serves as a property-value-provider for a feature of interest. The O&M schemata not only enable the definition of observations but also of phenomena. Based upon these definitions dictionaries can be designed which defines the phenomena used in a certain application domain. Such a dictionary forms the basis for a general understanding of sensor data.

Basic Observation Model

An observation comprises of the following key properties:

  • featureOfInterest - is a domain specific feature, which is a representation of the observation target, being the real-world object regarding which the observation is made.
  • observedProperty - describes the phenomenon for which the observation result provides an estimate of its value. It must be a property associated with the type of the feature of interest. In short this is called the property-value-provider concept.
  • procedure - is the description of a process used to generate the result.
  • result - contains the value generated by the procedure. This is in general an sensor, but may be a human observer or even a simulation model.

Further properties are

  • samplingTime - the time that the result applies to the featureOfInterest.
  • resultTime - the time when the procedure associated with the observation act was applied. If samplingTime and resultTime are identical the resultTime may be omitted.
  • parameter - is an event-specific parameter and is typically used to record environmental/event-specific sampling parameters parameters. E.g. the sampling height of air temperature measurements.
  • metadata - allows to attach any kind of metadata information to the observation.
  • resultQuality - allows for the encoding of quality information of the information
The basic observation model

Specialized Observations

The data type of the result in the basic observation model is of type Any. A series of specialized observations have been defined in order to restrict the data type of the result.

Measurement Example 

 <?xml version="1.0" encoding="windows-1250"?>
 <om:Measurement gml:id="obsTest"
 xmlns:om="http://www.opengis.net/om/1.0"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
 xmlns:xlink="http://www.w3.org/1999/xlink"
 xmlns:gml="http://www.opengis.net/gml"
 xsi:schemaLocation="http://www.opengis.net/om/1.0 ../extensions/observationSpecialization_override.xsd">
   <om:samplingTime>
     <gml:TimeInstant>
       <gml:timePosition>2008-10-14T00:09:53+02:00</gml:timePosition>
     </gml:TimeInstant>
   </om:samplingTime>
   <om:procedure 
   xlink:href="urn:ogc:object:feature:OSIRIS-HWS:a1ef1094-c201-4f9f-8f2e-0ff97bf65f03"/>
   <om:observedProperty xlink:href="urn:x-ogc:def:property:OGC::RelativeHumidity"/>
   <om:featureOfInterest>
     <sa:SamplingPoint 
     gml:id="urn:ogc:object:feature:OSIRIS-HWS:a1ef1094-c201-4f9f-8f2e-0ff97bf65f03" 
     xsi:type="ns:SamplingPointType" xmlns:ns="http://www.opengis.net/sampling/1.0" 
     xmlns:gml="http://www.opengis.net/gml">
       <gml:name>roof of the ifgi</gml:name>
       <sa:sampledFeature 
       xlink:href="urn:ogc:object:feature:OSIRIS-HWS:hygrometera1ef1094-c201-4f9f-8f2e-0ff97bf65f03"/>
       <sa:position>
         <gml:Point srsName="urn:ogc:def:crs:EPSG:4326">
           <gml:pos>52.07349 9.42125</gml:pos>
         </gml:Point>
       </sa:position>
     </sa:SamplingPoint>
   </om:featureOfInterest>
   <om:result uom="%" xlink:href="urn:x-ogc:def:uom:OGC:percent" >41</om:result>
 </om:Measurement>
Specializations of the basic observation model

CategoryObservation Example 

 <?xml version="1.0" encoding="windows-1250"?>
 <om:CategoryObservation gml:id="catObs-1979" 
 xmlns:om="http://www.opengis.net/om/1.0"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xmlns:xlink="http://www.w3.org/1999/xlink"
 xmlns:gml="http://www.opengis.net/gml"
 xsi:schemaLocation="http://www.opengis.net/om/1.0 ../extensions/observationSpecialization_override.xsd">
   <om:samplingTime>
     <gml:TimeInstant>
       <gml:timePosition>2009-09-16T17:22:25.00</gml:timePosition>
     </gml:TimeInstant>
   </om:samplingTime>
   <om:procedure xlink:href="urn:ogc:object:procedure:CITE:WeatherService:NYC"/>
   <om:observedProperty xlink:href="urn:ogc:def:phenomenon:OGC:1.0.30:skyWeather"/>
   <om:featureOfInterest/>
   <sa:SamplingPoint gml:id="urn:ogc:object:feature:FOI_NYC"
   xsi:type="ns:SamplingPointType"
   xmlns:ns="http://www.opengis.net/sampling/1.0"
   xmlns:gml="http://www.opengis.net/gml">
     <gml:name>Central Park</gml:name>
     <sa:sampledFeature xlink:href="urn:ogc:object:feature:FOI_NYC-aw1610"/>
     <sa:position>
       <gml:Point srsName="urn:ogc:crs:epsg:4326">
         <gml:pos>40.7833 -73.9667</gml:pos>
       </gml:Point>
     </sa:position>
   </sa:SamplingPoint>
   <om:result codeSpace="urn:ogc:def:phenomenon:OGC:1.0.30:skyWeather">Fair</om:result>
 </om:CategoryObservation>

GeometryObservation Example 

 <?xml version="1.0" encoding="windows-1250"?>
 <om:GeometryObservation gml:id="geom1610" 
 xmlns:om="http://www.opengis.net/om/1.0" 
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
 xmlns:xlink="http://www.w3.org/1999/xlink" 
 xmlns:gml="http://www.opengis.net/gml" 
 xsi:schemaLocation="http://www.opengis.net/om/1.0 ../extensions/observationSpecialization_override.xsd">
   <om:samplingTime>
     <gml:TimeInstant>
       <gml:timePosition>2009-09-16T17:22:25.00</gml:timePosition>
     </gml:TimeInstant>
   </om:samplingTime>
   <om:procedure xlink:href="urn:ogc:object:procedure:ifgi:GPS"/>
   <om:observedProperty xlink:href="urn:ogc:def:phenomenon:OGC:Shape"/>
   <om:featureOfInterest xlink:href="urn:ogc:object:feature:vehicle"/>
   <om:result>
     <gml:Point srsName="urn:ogc:crs:epsg:4326">
       <gml:pos>40.7833 -73.9667</gml:pos>
     </gml:Point>
   </om:result>
 </om:GeometryObservation>

Observation with SweDataArray

A compact encoding of observations is to use a SweDataArray as resultType. The SweDataArray allows to define a compact text block encoding. By means of the SimpleDataRecord the structure of the encoding is defined.

The following listing depicts an snippet of an obersvation with a SweDataArray as result. Click here to see the entire example. 

 <om:Observation gml:id="ot_34">
   <om:samplingTime>
     <gml:TimePeriod xsi:type="gml:TimePeriodType">
       <gml:beginPosition>2008-04-01T17:44:00.000+02:00</gml:beginPosition>
       <gml:endPosition>2008-06-01T19:44:15.000+02:00</gml:endPosition>
     </gml:TimePeriod>
   </om:samplingTime>
   <om:procedure xlink:href="urn:ogc:object:feature:Sensor:IFGI:ifgi-sensor-1"/>
   <om:observedProperty>
     <swe:CompositePhenomenon gml:id="cpid0" dimension="1">
       <gml:name>resultComponents</gml:name>
       <swe:component xlink:href="urn:ogc:data:time:iso8601"/>
       <swe:component xlink:href="urn:ogc:def:phenomenon:OGC:1.0.30:waterlevel"/>
     </swe:CompositePhenomenon>
   </om:observedProperty>
   <om:featureOfInterest>
     <gml:FeatureCollection>
       <gml:featureMember xlink:href="foi_sampSur_1001"/>
       <gml:featureMember>
         <sa:SamplingPoint gml:id="foi_1001">
           <gml:name>ALBER</gml:name>
           <sa:position>
             <gml:Point>
               <gml:pos srsName="urn:ogc:def:crs:EPSG:6.8:4326">7.52 52.9</gml:pos>
             </gml:Point>
           </sa:position>
         </sa:SamplingPoint>
       </gml:featureMember>
     </gml:FeatureCollection>
   </om:featureOfInterest>
   <om:result>
     <swe:DataArray>
       <swe:elementCount>
         <swe:Count>
           <swe:value>9</swe:value>
         </swe:Count>
       </swe:elementCount>
       <swe:elementType name="Components">
         <swe:SimpleDataRecord>
           <swe:field name="Time">
             <swe:Time definition="urn:ogc:data:time:iso8601"/>
           </swe:field>
           <swe:field name="feature">
             <swe:Text definition="urn:ogc:data:feature"/>
           </swe:field>
           <swe:field name="waterlevel">
             <swe:Quantity definition="urn:ogc:def:phenomenon:OGC:1.0.30:waterlevel">
               <swe:uom code="cm"/>
             </swe:Quantity>
           </swe:field>
         </swe:SimpleDataRecord>
       </swe:elementType>
       <swe:encoding>
         <swe:TextBlock decimalSeparator="." tokenSeparator="," blockSeparator=";"/>
       </swe:encoding>
       <swe:values>2008-04-01T17:44:00.000+02:00,foi_1001,50.0;2008-04-01T17:45:00.000+02:00,foi_1001,40.2;2008-04-01T17:46:00.000+02:00,foi_1001,70.4;2008-04-01T17:47:00.000+02:00,foi_1001,60.5;2008-04-01T17:48:00.000+02:00,foi_1001,45.456;2008-04-01T17:49:00.000+02:00,foi_1001,110.1213;2008-04-01T19:44:15.000+02:00,foi_sampSur_1001,10.0;2008-04-01T19:44:15.000+02:00,foi_1001,10.0;2008-05-01T19:44:15.000+02:00,foi_1001,10.0;2008-06-01T19:44:15.000+02:00,foi_1001,10.0;</swe:values>
     </swe:DataArray>
   </om:result>
 </om:Observation>
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