Spatial Data Warehouses - Data Warehouse Systems: Design and Implementation - page 435

More complex linear and surface objects use structures (lists, sets, or arrays)
based on the point representation.
The standard ISO/IEC 13249 SQL/MM is an extension of SQL:2003
for managing multimedia and application-specific packages. Part 3 of the
standard defines how to store, retrieve, and manipulate spatial data in a
relational database system. It defines how zero-, one-, or two-dimensional
spatial data values are represented on a two-dimensional (

R

2 ), three-

4 ) coordinate space. We describe
next the spatial data types defined by SQL/MM, which are used and extended
in PostGIS.

R

3 ), or four-dimensional (

R

dimensional (

ST_Geometry

ST_Geom
Collection

ST_Surface ST_Curve ST_Point

ST_Curve
Polygon

ST_Multi
Point

ST_Multi
Curve

ST_Multi
Surface

ST_Polyhedrl
Surface

ST_Multi
LineString

ST_Multi
Polygon

ST_Polygon

ST_Triangle ST_TIN

ST_Line
String

ST_Elliptical
Curve

ST_Compound
Curve

ST_Circle ST_Clothoid

ST_Circular
String

ST_Geodesic
String

ST_NURBS
Curve

ST_Spiral
Curve

Fig. 11.14 Hierarchy of spatial types in SQL/MM

Figure 11.14 shows the type hierarchy defined in the SQL/MM standard
for geometric features. ST Geometry is the root of the hierarchy, and
it is an abstract type. ST Point represents 0-dimensional geometries.
ST Curve is an abstract type representing 1-dimensional geometries. Several
subtypes of ST Curve are defined. ST LineString represents line segments
defined by a sequence of points using linear interpolation. ST CircularString
represents arc segments defined by a sequence of points using circular
interpolation. ST CompoundCurve represents a combination of linear and
circular strings. ST Circle represents circles defined by three noncollinear
points. ST GeodesicString represents arcs defined by a sequence of points
interpolated by geodesic curve segments. ST EllipticalCurve represents a single