(mysql.info.gz) GIS introduction
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(mysql.info.gz) Spatial extensions in MySQL
(mysql.info.gz) Spatial extensions in MySQL
(mysql.info.gz) OpenGIS geometry model
18.1 Introduction
=================
MySQL implements spatial extensions following the specification of the
`Open GIS Consortium' (OGC). This is an international consortium of
more than 250 companies, agencies, and universities participating in
the development of publicly available conceptual solutions that can be
useful with all kinds of applications that manage spatial data. The
OGC maintains a Web site at `http://www.opengis.org/'.
In 1997, the Open GIS Consortium published the `OpenGIS (R) 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 Open GIS Web site at
`http://www.opengis.org/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 specifications
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, a postcode area, the tropics.
* A definable location. For example, a crossroad, as a particular
place where two streets intersect.
You can also find documents that 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*. The term
most commonly used here is *geometry*.
Let's define a *geometry* as _a point or an aggregate of points
representing anything in the world that has a location_.
Info Catalog
(mysql.info.gz) Spatial extensions in MySQL
(mysql.info.gz) Spatial extensions in MySQL
(mysql.info.gz) OpenGIS geometry model
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