gml:AbstractDatumType

A datum specifies the relationship of a coordinate system to the earth, thus creating a coordinate reference system. A datum uses a parameter or set of parameters that determine the location of the origin of the coordinate reference system. Each datum subtype can be associated with only specific types of coordinate systems. This abstract complexType shall not be used, extended, or restricted, in an Application Schema, to define a concrete subtype with a meaning equivalent to a concrete subtype specified in this document. 

Complex type information

Content

• Sequence [1..1]
  from type gml:AbstractDatumBaseType
  gml:metaDataProperty [0..*]    Contains or refers to a metadata package that contains metadata properties.
  gml:datumName [1..1]    The name by which this datum is identified.
  1. gml:datumID [0..*]    Set of alternative identifications of this datum. The first datumID, if any, is normally the primary identification code, and any others are aliases.
  2. gml:remarks [0..1]    Comments on this reference system, including source information.
  3. gml:anchorPoint [0..1]    Description, possibly including coordinates, of the point or points used to anchor the datum to the Earth. Also known as the "origin", especially for engineering and image datums. The codeSpace attribute can be used to reference a source of more detailed on this point or surface, or on a set of such descriptions. - For a geodetic datum, this point is also known as the fundamental point, which is traditionally the point where the relationship between geoid and ellipsoid is defined. In some cases, the "fundamental point" may consist of a number of points. In those cases, the parameters defining the geoid/ellipsoid relationship have been averaged for these points, and the averages adopted as the datum definition. - For an engineering datum, the anchor point may be a physical point, or it may be a point with defined coordinates in another CRS. When appropriate, the coordinates of this anchor point can be referenced in another document, such as referencing a GML feature that references or includes a point position. - For an image datum, the anchor point is usually either the centre of the image or the corner of the image. - For a temporal datum, this attribute is not defined. Instead of the anchor point, a temporal datum carries a separate time origin of type DateTime.
  4. gml:realizationEpoch [0..1]    The time after which this datum definition is valid. This time may be precise (e.g. 1997.0 for IRTF97) or merely a year (e.g. 1983 for NAD83). In the latter case, the epoch usually refers to the year in which a major recalculation of the geodetic control network, underlying the datum, was executed or initiated. An old datum can remain valid after a new datum is defined. Alternatively, a datum may be superseded by a later datum, in which case the realization epoch for the new datum defines the upper limit for the validity of the superseded datum.
  5. gml:validArea [0..1]    Area or region in which this CRS object is valid.
  6. gml:scope [0..1]    Description of domain of usage, or limitations of usage, for which this CRS object is valid.

Attributes

Used by

• Element gml:_Datum
• Element gml:EngineeringDatum via derived type gml:EngineeringDatumType
• Element gml:GeodeticDatum via derived type gml:GeodeticDatumType
• Element gml:ImageDatum via derived type gml:ImageDatumType
• Element gml:TemporalDatum via derived type gml:TemporalDatumType
• Element gml:VerticalDatum via derived type gml:VerticalDatumType
• Element gmx:DatumAlt via derived type gmx:DatumAlt_Type
• Element gmx:ML_EngineeringDatum via derived type gmx:ML_EngineeringDatum_Type
• Element gmx:ML_GeodeticDatum via derived type gmx:ML_GeodeticDatum_Type
• Element gmx:ML_ImageDatum via derived type gmx:ML_ImageDatum_Type
• Element gmx:ML_TemporalDatum via derived type gmx:ML_TemporalDatum_Type
• Element gmx:ML_VerticalDatum via derived type gmx:ML_VerticalDatum_Type

Type inheritance chain

• gml:AbstractGMLType
  • gml:DefinitionType
    • gml:AbstractDatumBaseType
      • gml:AbstractDatumType
        • extended by gmx:DatumAlt_Type
        • extended by gml:EngineeringDatumType
          • extended by gmx:ML_EngineeringDatum_Type
        • extended by gml:ImageDatumType
          • extended by gmx:ML_ImageDatum_Type
        • extended by gml:VerticalDatumType
          • extended by gmx:ML_VerticalDatum_Type
        • extended by gml:GeodeticDatumType
          • extended by gmx:ML_GeodeticDatum_Type
        • restricted by gml:TemporalDatumBaseType
          • extended by gml:TemporalDatumType
            • extended by gmx:ML_TemporalDatum_Type