The geometry classes define a hierarchy as follows:
Geometry(noninstantiable)Point(instantiable)Curve(noninstantiable)LineString(instantiable)LineLinearRing
Surface(noninstantiable)Polygon(instantiable)
GeometryCollection(instantiable)MultiPoint(instantiable)MultiCurve(noninstantiable)MultiLineString(instantiable)
MultiSurface(noninstantiable)MultiPolygon(instantiable)
It is not possible to create objects in noninstantiable classes. It is possible to create objects in instantiable classes. All classes have properties, and instantiable classes may also have assertions (rules that define valid class instances).
Geometry is the base class. It is an abstract
class. The instantiable subclasses of
Geometry are restricted to zero-, one-, and
two-dimensional geometric objects that exist in two-dimensional
coordinate space. All instantiable geometry classes are defined
so that valid instances of a geometry class are topologically
closed (that is, all defined geometries include their boundary).
The base Geometry class has subclasses for
Point, Curve,
Surface, and
GeometryCollection:
Pointrepresents zero-dimensional objects.Curverepresents one-dimensional objects, and has subclassLineString, with sub-subclassesLineandLinearRing.Surfaceis designed for two-dimensional objects and has subclassPolygon.GeometryCollectionhas specialized zero-, one-, and two-dimensional collection classes namedMultiPoint,MultiLineString, andMultiPolygonfor modeling geometries corresponding to collections ofPoints,LineStrings, andPolygons, respectively.MultiCurveandMultiSurfaceare introduced as abstract superclasses that generalize the collection interfaces to handleCurvesandSurfaces.
Geometry, Curve,
Surface, MultiCurve, and
MultiSurface are defined as noninstantiable
classes. They define a common set of methods for their
subclasses and are included for extensibility.
Point, LineString,
Polygon,
GeometryCollection,
MultiPoint,
MultiLineString, and
MultiPolygon are instantiable classes.