Spatial Data Warehouses - Data Warehouse Systems: Design and Implementation - page 436

curve segment having elliptical interpolation. ST NURBSCurve represents a
nonuniform rational BSpline defined by a polynomial. ST Clothoid represents
a single curve segment having clothoid interpolation. ST SpiralCurve
represents a single curve segment having spiral interpolation.
ST Surface is an abstract type representing 2-dimensional geometries
composed by simple surfaces consisting of a single patch whose boundary is
specified by one exterior ring and zero or more interior rings if the surface has
holes. In the type ST CurvePolygon , the boundaries are any curve, while in the
type ST Polygon , the boundaries must be linear strings. ST Triangle ,represent
polygons composed of three linear strings. ST PolyhedrlSurface represents
surfaces formed by stitching together simple surfaces along their boundaries,
while ST TIN represents polyhedral surfaces composed only of triangles.
ST GeomCollection represents collections of zero or more ST Geometry
values. ST MultiPoint represents a collection of single points, not necessarily
distinct (i.e., a bag of points). Similarly, ST MultiCurve represents a bag
of ST Curve and ST MultiLineString a bag of ST LineString . Notice that
there are no types ST MultiCircularString and ST MultiCompoundCurve .The
types ST MultiSurface and ST MultiPolygon represent, respectively, sets of
curve polygons and sets of polygons with linear boundaries. In addition,
ST MultiSurface constrains its values to contain only disjoint surfaces.
The standard also defines a rich set of spatial methods and functions.
These can be grouped in several categories.
There are methods that retrieve properties or measures from a geometry.
Examples are ST Boundary for retrieving the boundary of a geometry and
ST Length for the length of a line string of a multiline string.
There are also methods that convert between geometries and external data
formats. Three external data formats are supported: well-known text repre-
sentation (WKT), well-known binary representation (WKB), and Geography
Markup Language (GML). For GML, for example, there are functions like
ST LineFromGML or ST MPointFromGML , which return, respectively, a line
or a multipoint value from its GML representation.
There are methods that compare two geometries with respect to their
spatial relation. These are ST Equals , ST Disjoint , ST Within , ST Touches ,
ST Crosses , ST Intersects , ST Overlaps ,and ST Contains . All these methods
return an integer value that can be 1 (true) or 0 (false).
There are also methods that generate new geometries from other ones.
The newly generated geometry can be the result of a set operation on
two geometries (e.g., ST Difference , ST Intersection , ST Union )orcanbe
calculated by some algorithm applied to a single geometry (e.g., ST Buffer ).
Finally, the SQL/MM standard defines an information schema that
provides a mechanism to determine the available spatial features. It consists
of the following four views:
1. ST GEOMETRY COLUMNS lists all columns in all tables that are of
type ST GEOMETRY or one of its subtypes as well as the optional SRS
associated with the column.