Observations and Measurements

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Observations and Measurements (O&M) is an Open Geospatial Consortium standard[1] which defines a conceptual schema and XML encoding for observations, and for features involved in sampling when making observations. While the O&M standard was developed in the context of geographic information systems, the model is derived from generic patterns proposed by Fowler and Odell[2], and is not limited to spatial information. O&M is one of the core standards in the OGC Sensor Web Enablement suite, providing the response model for Sensor Observation Service[3] (SOS) which scopes the SOS GetObservation request.


Observation Schema

Part 1[4] of the standard provides the Observation schema. An observation is an act that results in the estimation of the value of a feature property, and involves application of a specified procedure, such as a sensor, instrument, algorithm or process chain. The procedure may be applied in-situ, remotely, or ex-situ with respect to the sampling location. Use of a common model allows observation data using different procedures to be combined unambiguously. Observation details are also important for data discovery and for data quality estimation. An observation is defined in terms of the set of properties that support these applications. The Observation model takes a user-centric viewpoint, emphasizing the semantics of the feature-of-interest and its properties. This contrasts with sensor oriented models such as SensorML, which take a process- and thus provider-centric viewpoint.

O&M defines a core set of properties for an observation:

  • feature of interest
  • observed property
  • result
  • procedure - the instrument, algorithm or process used (which may be described using SensorML)
  • sampling time - the real-world time associated with the result
  • result time - the time when the result was generated

The key to the model is the separation of the observation and its feature of interest, separating the concerns so that the appropriate information associated with the description of each object. This allows a unified treatment of in situ, ex-situ, and remote-sensed observations.

The observation schema may also be understood as a corollary of the General Feature Model from ISO 19101[5], providing metadata associated with the estimation of the value of a feature property.

Sampling Features

Part 2[6] of the standard provides a schema for Sampling Features. Observations commonly involve sampling of the ultimate feature of interest. Specific sampling features, such as station, specimen, transect, section, are used in many application domains, and common processing and visualization tools are used. This standard defines a common set of sampling feature types classified primarily by spatial dimension, as well as samples for ex-situ observations. The schema includes relationships between sampling features (sub-sampling, derived samples).

The core properties of sampling features are:

  • sampled feature - which links the sampling artefact with the real-world feature of interest
  • related observation
  • related sampling feature - linking sampling features into complexes

Data transfer

An XML encoding (GML Application Schema) is provided for transfer of data:

Future plans

O&M Version 2 is a project in ISO Technical Committee 211, and has been assigned the number ISO 19156. Publication as an international standard is expected in 2011[7].

See also


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