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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.)
A geometry value has the following properties:
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.
((MINX MINY, MAXX MINY, MAXX MAXY, MINX MAXY, MINX MINY)) |
LineString
, MultiPoint
,
MultiLineString
)
are either simple or non-simple. Each type determines its own assertions
for being simple or non-simple.
LineString
, MultiString
) are
either closed
or not closed. Each type determines its own assertions for being closed
or not closed.
NULL
value).
An empty geometry is defined to be always simple and has an area of 0.
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.
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