11.3 Supported Spatial Data Formats

This section describes the standard spatial data formats that are used to represent geometry objects in queries. They are:

• Well-Known Text (WKT) format
• Well-Known Binary (WKB) format

Internally, MySQL stores geometry values in a format that is not identical to either WKT or WKB format.

11.3.1 Well-Known Text (WKT) Format

The Well-Known Text (WKT) representation of Geometry is designed to exchange geometry data in ASCII form.

Examples of WKT representations of geometry objects are:

• A Point:

  POINT(15 20)

  Note that point coordinates are specified with no separating comma.

• A LineString with four points:

  LINESTRING(0 0, 10 10, 20 25, 50 60)

• A Polygon with one exterior ring and one interior ring:

  POLYGON((0 0,10 0,10 10,0 10,0 0),(5 5,7 5,7 7,5 7, 5 5))

• A MultiPoint with three Point values:

  MULTIPOINT(0 0, 20 20, 60 60)

• A MultiLineString with two LineString values:

  MULTILINESTRING((10 10, 20 20), (15 15, 30 15))

• A MultiPolygon with two Polygon values:

  MULTIPOLYGON(((0 0,10 0,10 10,0 10,0 0)),((5 5,7 5,7 7,5 7, 5 5)))

• A GeometryCollection consisting of two Point values and one LineString:

  GEOMETRYCOLLECTION(POINT(10 10), POINT(30 30), LINESTRING(15 15, 20 20))

A Backus-Naur grammer that specifies the formal production rules for writing WKT values may be found in the OGC specification document referenced near the beginning of this chapter.

11.3.2 Well-Known Binary (WKB) Format

The Well-Known Binary (WKB) representation for geometric values is defined by the OpenGIS specifications. 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 1-byte unsigned integers, 4-byte unsigned integers, and 8-byte double-precision numbers (IEEE 754 format). A byte is 8 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.

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