18.3.2. Well-Known Binary (WKB) Format
The Well-Known Binary (WKB) representation for geometric values
is defined by the OpenGIS specification. It is also defined in
the ISO SQL/MM Part 3: Spatial standard.
WKB is used to exchange geometry data as binary streams
represented by BLOB values containing
geometric WKB information.
WKB uses one-byte unsigned integers, four-byte unsigned
integers, and eight-byte double-precision numbers (IEEE 754
format). A byte is eight bits.
For example, a WKB value that corresponds to POINT(1
1) consists of this sequence of 21 bytes (each
represented here by two hex digits):
0101000000000000000000F03F000000000000F03F
The sequence may be broken down into these components:
Byte order : 01
WKB type : 01000000
X : 000000000000F03F
Y : 000000000000F03F
Component representation is as follows:
The byte order may be either 0 or 1 to indicate
little-endian or big-endian storage. The little-endian and
big-endian byte orders are also known as Network Data
Representation (NDR) and External Data Representation (XDR),
respectively.
The WKB type is a code that indicates the geometry type.
Values from 1 through 7 indicate Point,
LineString, Polygon,
MultiPoint,
MultiLineString,
MultiPolygon, and
GeometryCollection.
A Point value has X and Y coordinates,
each represented as a double-precision value.
WKB values for more complex geometry values are represented by
more complex data structures, as detailed in the OpenGIS
specification.
