(mysql.info.gz) GIS class geometry

Info Catalog

(mysql.info.gz) GIS geometry class hierarchy

(mysql.info.gz) OpenGIS geometry model

(mysql.info.gz) GIS class point

 
 18.2.2 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.)
 
 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.
 
      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
      *geocentric* system (coordinates on the Earth's surface) are
      different things.
 
    * Its *interior*, *boundary*, and *exterior*.  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 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))
 
    * Whether the value is *simple* or *non-simple*.  Geometry values of
      types (`LineString', `MultiPoint', `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 (`LineString', `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 `MultiPoint', `MultiLineString', and
      `MultiPolygon' objects are the same as the dimensions of the
      elements they consist of.
 
 

Info Catalog

(mysql.info.gz) GIS geometry class hierarchy

(mysql.info.gz) OpenGIS geometry model

(mysql.info.gz) GIS class point