16.3. Supported Spatial Data Formats

MySQL 5.0

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16.3. 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.

16.3.1. 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:

  • A : 

    POINT(15 20)

    Note that point coordinates are specified with no separating comma.

  • A with four points: 

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

    Note that point coordinate pairs are separated by commas.

  • A 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 with three values: 

    MULTIPOINT(0 0, 20 20, 60 60)

  • A with two values: 

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

  • A with two values: 

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

  • A consisting of two values and one : 

    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.

16.3.2. 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 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 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 , , , , , , and .

  • A 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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