Coverage Data - Coverage Model

Coverage Model

Formally, in GMLCOV AbstractCoverage is a subtype of AbstractFeature (indicating its close relation). An abstract coverage consists of the following components:

• coverage domain: the extent where valid values are available;
• range set: the set of values ("pixels", "voxels") the coverage consists of, together with their locations
• range type: a type definition of the range set values
• metadata: a slot where any kind of metadata can be added

This abstract coverage is refined into several concrete coverage types, which can be instantiated, for example:

• gridded coverages:

• GridCoverage: a regular, equispaced grid which is not spatially referenced (like a raster image which has no geo coordinates associated)
• RectifiedGridCoverage: a regular, equispaced grid which is spatially referenced (like a satellite image which does have geo coordinates associated)
• ReferenceableGridCoverage: a grid which is not noecessarily equispaced (like satellite image time series where images do not arrive at regular time intervals, or curvilinear grids following river estuaries)

• multi-feature coverages:

• MultiPointCoverage: sets of values associated with points located in space/time ("point clouds")
• MultiCurveCoverage: sets of values associated with curves located in space/time (such as trajectories)
• MultiSurfaceCoverage: sets of values associated with surfaces located in space/time (such as iso-surfaces)
• MultiSolidCoverage: sets of values associated with solids located in space/time (such as CAD objects)

Among the special cases which can be modelled by coverages are

• set of Thiessen polygons, used to analyse spatially distributed data such as rainfall measurements
• triangulated irregular network (TIN), often used for terrain models