2.2.2 Coordinate Reference System (CRS)

RESQML uses both global (projected) and local coordinate reference systems. A CRS is a top-level data object in the RESQML data model (for more information, see 3.2.1 RESQML Data Objects ).

• Global CRS. From the perspective of an earth modeler, use of a global CRS allows models to be accurately located on the earth. The global CRS is a projected 2D CRS specified using either EPSG codes (see below) or, if you have a coordinate reference system that does not have EPSG codes, then use the Geographic Markup Language (GML) (see below). For work where location in the world is irrelevant, you can specify "unknown."

BUSINESS RULE: For a RESQML dataset, only one projected 2D CRS is allowed in an EPC file. Local CRS transformations are supported (see below).

• Local CRS. Each data object that contains geometric information must be specified with respect to a local coordinate reference system, which is defined relative to the projected 2D CRS (with optional rotation and translation). A local CRS vertical axis may represent depth, elevation, or time. Several local CRSs are allowed inside a package. Conversion between local CRSs requires only simple translations and rotations. RESQML requires at least one local 3D CRS.

For more information, see the Energistics Coordinate Reference System Usage Guide.