Requirements class: Monitoring Point feature of interest Requirements Class Requirements class: Sampling Feature Collections Requirements Class

Copyright © 2012 Open Geospatial Consortium 64

9.19.10 verticalDatum

Specifies the elevation that is used as the zero point, or datum, for stage measurements. The datum is defined using a vertical datum, which may be defined using the ISO19111 type CD_VerticalDatum, or an agreed upon datum may be reference by its identifier. E.g. the Australian Height Datum AHD, Tasmania = “EPSG::5112”. The CD_VerticalDatum type allows specification of the local gauge zero as a height above a reference datum. E.g. local gauge zero is 23m above the AHD.

9.20 Requirements class: Monitoring Point feature of interest Requirements Class

http:www.opengis.netspecwaterml2.0requml-monitoring-point-feature-of-interest Target Type Encoding of the conceptual model Name Monitoring point Dependency urn:iso:dis:iso:19156:clause:9 Requirement requml-monitoring-point-feature-of-interestfoi The target of the featureOfInterest property of the TimeseriesObservation shall be a MonitoringPoint type or a reference to an object of this type. Most direct timeseries observations in hydrology use a monitoring point to sample a domain feature e.g. edge of a river, on a point on a lake etc.. This requirements class describes this case. This restriction is not captured in the core timeseries observation requirements class, as it is common for derived observations to have a feature of interest as the domain feature e.g. a derived storage volume measurement is a direct ‘observation’ of the storage’s volume property.

9.21 Requirements class: Sampling Feature Collections Requirements Class

http:www.opengis.netspecwaterml2.0requml-sampling-feature-collections Target Type Encoding of the conceptual model Name Sampling feature collections Dependency urn:iso:dis:iso:19156:clause:9 Requirement requml-sampling-feature-collectionsgroups Groups of sampling points shall be described using SamplingFeatureCollection feature type from ISO19156. OGC WaterML 2.0 OGC 10-126r3 Copyright © 2012 Open Geospatial Consortium 65 Defining groups of sampling points is often required, allowing multiple sampling points to be associated with a particular identifier or name. This is common in hydrology as organisations often have a number of sampling points often closely located that may be named for the purposes of site visits, maintenance or reporting. A SamplingFeatureCollection is how a group such as a “field site with many sampling locations” would be expressed. Figure 32 - SF_SamplingFeatureCollection as defined by ISO19156 A sampling group may be defined by fully defining each of the sampling features contained in the group, or by referencing each of the sampling points in the group. It is possible to implement sampling groups in both directions: When defining the sampling point, include a relation to the sampling features in the group using the relatedSamplingFeature property. Define a SF_SamplingFeatureCollection that contains the sampling points. Note: this can be done by referencing already defined sampling points through an identifier or by defining the containing points directly inline. The two approaches are useful in different scenarios; guidance on their use is expanded in examples and future best practice guides.

9.22 Requirements class: Observation process Requirements Class