4.3.2 Local Coordinates Reference Systems

To avoid numerical issues when computing relative distance between elements of a model, it is common practice in reservoir modeling to work within a local coordinate system. In RESQML, this local coordinate system is obtained by translation of the origin and areal rotation from projected and vertical global coordinate systems. It is also common to see elements in both the depth and the time domain.

RESQML contains one abstract class, AbstractLocal3dCrs, which references the projected and vertical CRS it is based on. Because some projected and vertical CRSs can be anonymous, it also contains information such as units of measure, axis order, and orientation. Most of the time, this information is redundant with the actual projected and vertical CRS definition, but is required for an anonymous CRS and is also targeted toward applications that are not CRS aware. In any case, such information in the local CRS must match its projected and vertical CRS.

The two concrete specializations of the AbstractLocal3dCrs allow separation between the depth and time domains.

• LocalDepth3dCRS is referred by representations in the depth domain

• LocalTime3dCrs is used by the representations in the time domain. LocalTime3dCrs also provides the unit of measure for time coordinates.

NOTE: When a CRS description is based on GML, it must include gml:identifier and the identifier must follow the UUID convention, so that a reader can quickly identify which representations are in the same CRS. (For more information on GML, see 2.2.2.2 Geographic Markup Language .)