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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.

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

Examples of WKT representations of geometry objects:

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)

Note that point coordinate pairs are separated by commas.

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`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))

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`MultiPoint`

with three`Point`

values:MULTIPOINT(0 0, 20 20, 60 60)

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`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 grammar that specifies the formal production rules for writing WKT values can be found in the OpenGIS specification document referenced near the beginning of this chapter.

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.