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
11.2.2 Class Geometry
Geometry is the root class of the hierarchy. It is a
non-instantiable class but has a number of properties that are common to
all geometry values created from any of the Geometry subclasses.
These properties are described in the following list. (Particular
subclasses have their own specific properties, described later.)
11.2.3 Geometry properties
A geometry value has the following properties:
- Its type. Each geometry belongs to one of the instantiable classes in the hierarchy.
- Its SRID, or Spatial Reference Identifier. This value identifies the geometry's associated Spatial Reference System that describes the coordinate space in which the geometry object is defined.
- Its coordinates in its Spatial Reference System, represented as double-precision (8-byte) numbers. All non-empty geometries include at least one pair of (X,Y) coordinates. Empty geometries contain no coordinates. Coordinates are related to the SRID. For example, in different coordinate systems, the distance between two objects may differ even when objects have the same coordinates, because the distance on the planar coordinate system and the distance on the geocentric system (coordinates on the Earth's surface) are different things.
- Its interior, boundary, and exterior. All geometries occupy some position in space. The exterior of a geometry is all space not occupied by the geometry. The interior is the space occupied by the geometry. The boundary is the interface between geometry's interior and exterior.
-
Its MBR (Minimum Bounding Rectangle), or Envelope.
This is the bounding geometry, formed by the minimum and maximum (X,Y)
coordinates:
((MINX MINY, MAXX MINY, MAXX MAXY, MINX MAXY, MINX MINY))
-
The quality of being simple or non-simple.
Geometry values of some types (
LineString,MultiPoint,MultiLineString)are either simple of non-simple. Each type determines its own assertions for being simple or non-simple. -
The quality of being closed or not closed.
Geometry values of some types (
LineString,MultiString) are either closed or not closed. Each type determines its own assertions for being closed or not closed. -
The quality of being empty or not empty
A geometry is empty if it does not have any points.
Exterior, interior and boundary of an empty geometry
are not defined (that is, they are represented by a
NULLvalue). An empty geometry is defined to be always simple and has an area of 0. -
Its dimension. A geometry can have a dimension of -1, 0, 1,
or 2:
- -1 stands for empty geometries.
- 0 stands for geometries with no length and no area.
- 1 stands for geometries with non-zero length and zero area.
- 2 stands for geometries with non-zero area.
Pointobjects have a dimension of zero.LineStringobjects have a dimension of 1.Polygonobjects have a dimension of 2. The dimensions ofMultiPoint,MultiLineString, andMultiPolygonobjects are the same as the dimensions of the elements they consist of.
