The ST_GEOMETRY type is the maximal supertype of the geometry type hierarchy. The ST_GEOMETRY type supports methods that
can be applied to any spatial value. The ST_GEOMETRY type cannot be instantiated; instead, a subtype should be instantiated.
When working with original formats (WKT or WKB), you can use methods such as ST_PointFromText/ST_PointFromWKB to instantiate
the appropriate concrete type representing the value in the original format.
The ST_SRID method can be used to retrieve the spatial reference system associated with the value.
Columns of the ST_GEOMETRY type or any of its subtypes cannot be included in a primary key, unique index, or unique constraint.
UltraLite provides a fixed set of three different reference systems that can be attributed to a column during its creation.
Individual geometry objects can be associated with any SRID value except the undefined reference system, and can only be stored
in a column associated with a matching SRID value or the undefined reference system.
The predefined reference systems are:
Undefined or "null" reference system
This is the default reference system if no SRID value is provided. It allows contained geometry values to be in any
valid reference system. This reference system allows for catch-all columns that do not enforce any reference system consistency
among their geometry objects.
Default planar reference system
Defined by specifying a SRID value of 0 during column creation, this column can contain only geometry values associated
with this reference system. The values are treated as being in 2D planar space.
WGS 84 Geodetic Reference System
Defined by specifying a SRID value of 4326 during column creation, this column can only contain geometry values associated
with this reference system. The values are treated as being on the Earth's surface and operations are applied accordingly.
A point in SRID 4326 can be stored in a column with the WGS 84 reference system or with the undefined reference system, but
not in the default planar system.
No transformations between reference systems are supported.