The Opengis Geometry Model - Oracle 5.0 Reference Manual

with all kinds of applications that manage spatial data. The OGC maintains a Web site at
www.opengis.org/.
In 1997, the Open Geospatial Consortium published the OpenGIS® Simple Features Specifications
For SQL, a document that proposes several conceptual ways for extending an SQL RDBMS to
support spatial data. This specification is available from the OGC Web site at
docs/99-049.pdf. It contains additional information relevant to this chapter.
MySQL implements a subset of the SQL with Geometry Types environment proposed by OGC. This
term refers to an SQL environment that has been extended with a set of geometry types. A geometry-
valued SQL column is implemented as a column that has a geometry type. The specification describe a
set of SQL geometry types, as well as functions on those types to create and analyze geometry values.
A geographic feature is anything in the world that has a location. A feature can be:
• An entity. For example, a mountain, a pond, a city.
• A space. For example, town district, the tropics.
• A definable location. For example, a crossroad, as a particular place where two streets intersect.
Some documents use the term geospatial feature to refer to geographic features.
Geometry is another word that denotes a geographic feature. Originally the word geometry meant
measurement of the earth. Another meaning comes from cartography, referring to the geometric
features that cartographers use to map the world.
This chapter uses all of these terms synonymously: geographic feature, geospatial feature, feature,
or geometry. Here, the term most commonly used is geometry, defined as a point or an aggregate of
points representing anything in the world that has a location.

12.16.2. The OpenGIS Geometry Model

The set of geometry types proposed by OGC's SQL with Geometry Types environment is based
on the OpenGIS Geometry Model. In this model, each geometric object has the following general
properties:
• It is associated with a Spatial Reference System, which describes the coordinate space in which the
object is defined.
• It belongs to some geometry class.
12.16.2.1. The Geometry Class Hierarchy
The geometry classes define a hierarchy as follows:
•
Geometry
•
Point
•
Curve
•
LineString
•
Line
•
LinearRing
•
Surface
•
Polygon
The OpenGIS Geometry Model
(noninstantiable)
(instantiable)
(noninstantiable)
(instantiable)
(noninstantiable)
(instantiable)
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http://
http://www.opengis.org/