Interface  Description 

Boundary 
The abstract root data type for all the data types used to represent the boundary of geometric
objects.

BoundingBox 
Represents a twodimensional envelope.

BoundingBox3D 
Represents a threedimensional envelope.

DirectPosition 
Holds the coordinates for a position within some coordinate reference system.

Envelope 
A minimum bounding box or rectangle.

Geometry 
Root class of the geometric object taxonomy.

PositionFactory 
A factory for managing direct position creation.

Precision 
Specifies the precision model of the direct positions
in a geometry.

PrecisionFactory 
A factory for managing direct position creation.

TransfiniteSet 
A possibly infinite set; restricted only to values.

Class  Description 

PrecisionType 
The rounding policy used for a precision model.

Exception  Description 

MismatchedDimensionException 
Indicates that an operation cannot be completed properly because
of a mismatch in the dimensions of object attributes.

MismatchedReferenceSystemException 
Indicates that an object cannot be constructed because of a mismatch in the
reference systems of
geometric components.

UnmodifiableGeometryException 
Indicates that an operation is not allowed on a geometry object
because it is unmodifiable.

The geometry packages contain the various classes for coordinate geometry.
All of these classes through the root class Geometry
inherit an optional
association to a coordinate reference system. All direct positions exposed through the interfaces
defined in this specification shall be in the coordinate reference system of the geometric object
accessed. All elements of a geometric complex, composite, or aggregate shall be associated to the
same coordinate reference system. When instances of Geometry
are aggregated
in another Geometry
(such as a Aggregate
,
or Complex
) which already has a coordinate reference system specified,
then these elements are assumed to be in that same coordinate reference system unless otherwise
specified.
The geometry package has several internal packages that separate primitive geometric objects, aggregates and complexes, which have a more elaborate internal structure than simple aggregates.
Any object that inherits the semantics of the Geometry
acts as a set of direct positions. Its behavior will be determined by which direct positions it
contains. Objects under Primitive
will be open, that is, they
will not contain their boundary points; curves will not contain their end points, surfaces will
not contain their boundary curves, and solids will not contain their bounding surfaces. Objects
under Complex
will be closed, that is, they will contain their
boundary points. This leads to some apparent ambiguity. A representation of a line as a primitive
must reference its end points, but will not contain these points as a set of direct positions. A
representation of a line as a complex will also reference its end points, and will contain these
points as a set of direct positions. This means that identical digital representations will have
slightly different semantics depending on whether they are accessed as primitives or complexes.
This difference of semantics is most striking in the
CompositeCurve
. Composite curves are used to represent features whose
geometry could also be represented as curve primitives. From a cartographic point of view, these
two representations are not different. From a topological point of view, they are different. This
distinction appears as an inheritance relationship between CompositeCurve
and OrientableCurve
. The primary semantics of a
CompositeCurve
is as a closed Geometry
, but it
may also act as an open Geometry
under Primitive
operations. Interface protocols depending upon the topological details of this object will have to
be distinguished as to whether they have been inherited from Primitive
or Complex
, where the distinction first occurs. Even though these protocols
have been inherited from the same operations defined at Geometry
, they will act
differently depending upon the branch of the inheritance tree from which they have inherited semantics.
Creators of implementation profiles may take this into account and use a proxy mechanism for realization
relationships that cause semantic dissonance.
Geometry
and Primitive
are purely abstract in the sense that no object or data structure from an application can
instantiate them directly. Instances of these classes must be instances of one of their nonabstract
subtypes, such as Point
, Curve
, or
Surface
. This is not the case for Complex
,
which can be directly instantiated by an application, and need not be an instance of one of the
nonabstract subclasses of Composite
.
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