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.
In MySQL, the SRID value is just an integer associated with
the geometry value. All calculations are done assuming
Euclidean (planar) geometry.
Its coordinates in its
Spatial Reference System, represented as double-precision
(eight-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
(coordinates on the Earth's surface) are different things.
Every geometry occupies 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 the geometry's interior and
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))
Whether the value is simple
or non-simple. Geometry
values of types (
MultiLineString) are either simple or
non-simple. Each type determines its own assertions for
being simple or non-simple.
Whether the value is closed
or not closed. Geometry
values of types (
MultiString) are either closed or not
closed. Each type determines its own assertions for being
closed or not closed.
Whether the value is empty
or non-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
NULL value). 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 for an empty geometry.
0 for a geometry with no length and no area.
1 for a geometry with non-zero length and zero area.
2 for a geometry with non-zero area.
Point objects have a dimension of zero.
LineString objects have a dimension of 1.
Polygon objects have a dimension of 2.
The dimensions of
MultiPolygon objects are the same as the
dimensions of the elements they consist of.