MySQL Manual
11 Spatial Extensions in MySQL
- 11.2 The OpenGIS Geometry Model
- 11.2.1 The Geometry Class Hierarchy
- 11.2.2 Class
Geometry - 11.2.4 Class
Point - 11.2.7 Class
Curve - 11.2.9 Class
LineString - 11.2.12 Class
Surface - 11.2.14 Class
Polygon - 11.2.17 Class
GeometryCollection - 11.2.18 Class
MultiPoint - 11.2.21 Class
MultiCurve - 11.2.23 Class
MultiLineString - 11.2.25 Class
MultiSurface - 11.2.27 Class
MultiPolygon
11.2.1 The Geometry Class Hierarchy
The geometry classes define a hierarchy as follows:
Geometry(non-instantiable)Point(instantiable)Curve(non-instantiable)LineString(instantiable)LineLinearRing
Surface(non-instantiable)Polygon(instantiable)
GeometryCollection(instantiable)MultiPoint(instantiable)MultiCurve(non-instantiable)MultiLineString(instantiable)
MultiSurface(non-instantiable)MultiPolygon(instantiable)
Some of these classes are abstract (non-instantiable). That is, it is not possible to create an object of these classes. Other classes are instantiable and objects may be created of them. Each class has properties and instantiable classes may have assertions (rules that define valid class instances).
Geometry is the base class. It's 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 specialised zero-, one-, and two-dimensional collection classes namedMultiPoint,MultiLineString, andMultiPolygonfor modelling geometries corresponding to collections ofPoints,LineStrings, andPolygons, respectively.MultiCurveandMultiSurfaceare introduced as abstract superclasses that generalise the collection interfaces to handleCurvesandSurfaces.
Geometry, Curve, Surface, MultiCurve,
and MultiSurface are defined as non-instantiable classes.
They define a common set of methods for their subclasses and
are included for the reason of extensibility.
Point, LineString, Polygon, GeometryCollection,
MultiPoint, MultiLineString, and
MultiPolygon are instantiable classes.
