Table of Contents
GeometryPointCurveLineStringSurfacePolygonGeometryCollectionMultiPointMultiCurveMultiLineStringMultiSurfaceMultiPolygonGeometry Functions
MySQL supports spatial extensions to allow the generation, storage,
and analysis of geographic features. Before MySQL 5.0.16, these
features are available for MyISAM tables only. As
of MySQL 5.0.16, InnoDB, NDB,
BDB, and ARCHIVE also support
spatial features. (However, the ARCHIVE engine
does not support indexing, so spatial columns in
ARCHIVE columns cannot be indexed.)
This chapter covers the following topics:
The basis of these spatial extensions in the OpenGIS geometry model
Data formats for representing spatial data
How to use spatial data in MySQL
Use of indexing for spatial data
MySQL differences from the OpenGIS specification
If you have questions or concerns about about the use of the spatial extensions to MySQL, you can discuss these in the GIS forums on our website.
MySQL implements spatial extensions following the specification of
the Open GIS Consortium (OGC). This is an
international consortium of more than 250 companies, agencies, and
universities participating in the development of publicly
available conceptual solutions that can be useful with all kinds
of applications that manage spatial data. The OGC maintains a Web
site at http://www.opengis.org/.
In 1997, the Open GIS Consortium published the OpenGIS® Simple Features Specifications For SQL, a document that proposes several conceptual ways for extending an SQL RDBMS to support spatial data. This specification is available from the Open GIS Web site at http://www.opengis.org/docs/99-049.pdf. It contains additional information relevant to this chapter.
MySQL implements a subset of the SQL with Geometry Types environment proposed by OGC. This term refers to an SQL environment that has been extended with a set of geometry types. A geometry-valued SQL column is implemented as a column that has a geometry type. The specifications describe a set of SQL geometry types, as well as functions on those types to create and analyze geometry values.
A geographic feature is anything in the world that has a location. A feature can be:
An entity. For example, a mountain, a pond, a city.
A space. For example, a postcode area, the tropics.
A definable location. For example, a crossroad, as a particular place where two streets intersect.
You can also find documents that use the term geospatial feature to refer to geographic features.
Geometry is another word that denotes a geographic feature. Originally the word geometry meant measurement of the earth. Another meaning comes from cartography, referring to the geometric features that cartographers use to map the world.
This chapter uses all of these terms synonymously: geographic feature, geospatial feature, feature, or geometry. The term most commonly used here is geometry.
Let's define a geometry as a point or an aggregate of points representing anything in the world that has a location.
GeometryPointCurveLineStringSurfacePolygonGeometryCollectionMultiPointMultiCurveMultiLineStringMultiSurfaceMultiPolygonThe set of geometry types proposed by OGC's SQL with Geometry Types environment is based on the OpenGIS Geometry Model. In this model, each geometric object has the following general properties:
It is associated with a Spatial Reference System, which describes the coordinate space in which the object is defined.
It belongs to some geometry class.
The geometry classes define a hierarchy as follows:
Geometry (non-instantiable)
Point (instantiable)
Curve (non-instantiable)
LineString (instantiable)
Line
LinearRing
Surface (non-instantiable)
Polygon (instantiable)
GeometryCollection (instantiable)
MultiPoint (instantiable)
MultiCurve (non-instantiable)
MultiLineString
(instantiable)
MultiSurface (non-instantiable)
MultiPolygon (instantiable)
It is not possible to create objects in non-instantiable classes. It is possible to create objects in instantiable classes. All classes have properties, and instantiable classes may also have assertions (rules that define valid class instances).
Geometry is the base class. It's an abstract
class. The instantiable subclasses of
Geometry are restricted to zero-, one-, and
two-dimensional geometric objects that exist in two-dimensional
coordinate space. All instantiable geometry classes are defined
so that valid instances of a geometry class are topologically
closed (that is, all defined geometries include their boundary).
The base Geometry class has subclasses for
Point, Curve,
Surface, and
GeometryCollection:
Point represents zero-dimensional
objects.
Curve represents one-dimensional objects,
and has subclass LineString, with
sub-subclasses Line and
LinearRing.
Surface is designed for two-dimensional
objects and has subclass Polygon.
GeometryCollection has specialized zero-,
one-, and two-dimensional collection classes named
MultiPoint,
MultiLineString, and
MultiPolygon for modeling geometries
corresponding to collections of Points,
LineStrings, and
Polygons, respectively.
MultiCurve and
MultiSurface are introduced as abstract
superclasses that generalize the collection interfaces to
handle Curves and
Surfaces.
Geometry, Curve,
Surface, MultiCurve, and
MultiSurface are defined as non-instantiable
classes. They define a common set of methods for their
subclasses and are included for extensibility.
Point, LineString,
Polygon,
GeometryCollection,
MultiPoint,
MultiLineString, and
MultiPolygon are instantiable classes.
Geometry is the root class of the hierarchy.
It is a non-instantiable class but has a number of properties
that are common to all geometry values created from any of the
Geometry subclasses. These properties are
described in the following list. (Particular subclasses have
their own specific properties, described later.)
Geometry Properties
A geometry value has the following properties:
Its type. Each geometry belongs to one of the instantiable classes in the hierarchy.
Its SRID, or Spatial Reference Identifier. This value identifies the geometry's associated Spatial Reference System that describes the coordinate space in which the geometry object is defined.
In MySQL, the SRID value is just an integer associated with the geometry value. All calculations are done assuming Euclidean (planar) geometry.
Its coordinates in its Spatial Reference System, represented as double-precision (eight-byte) numbers. All non-empty geometries include at least one pair of (X,Y) coordinates. Empty geometries contain no coordinates.
Coordinates are related to the SRID. For example, in different coordinate systems, the distance between two objects may differ even when objects have the same coordinates, because the distance on the planar coordinate system and the distance on the geocentric system (coordinates on the Earth's surface) are different things.
Its interior, boundary, and exterior.
Every geometry occupies some position in space. The exterior of a geometry is all space not occupied by the geometry. The interior is the space occupied by the geometry. The boundary is the interface between the geometry's interior and exterior.
Its MBR (Minimum Bounding Rectangle), or Envelope. This is the bounding geometry, formed by the minimum and maximum (X,Y) coordinates:
((MINX MINY, MAXX MINY, MAXX MAXY, MINX MAXY, MINX MINY))
Whether the value is simple
or non-simple. Geometry
values of types (LineString,
MultiPoint,
MultiLineString) are either simple or
non-simple. Each type determines its own assertions for
being simple or non-simple.
Whether the value is closed
or not closed. Geometry
values of types (LineString,
MultiString) are either closed or not
closed. Each type determines its own assertions for being
closed or not closed.
Whether the value is empty
or non-empty A geometry is
empty if it does not have any points. Exterior, interior,
and boundary of an empty geometry are not defined (that is,
they are represented by a NULL value). An
empty geometry is defined to be always simple and has an
area of 0.
Its dimension. A geometry can have a dimension of −1, 0, 1, or 2:
−1 for an empty geometry.
0 for a geometry with no length and no area.
1 for a geometry with non-zero length and zero area.
2 for a geometry with non-zero area.
Point objects have a dimension of zero.
LineString objects have a dimension of 1.
Polygon objects have a dimension of 2.
The dimensions of MultiPoint,
MultiLineString, and
MultiPolygon objects are the same as the
dimensions of the elements they consist of.
A Point is a geometry that represents a
single location in coordinate space.
Point
Examples
Imagine a large-scale map of the world with many cities. A
Point object could represent each city.
On a city map, a Point object could
represent a bus stop.
Point
Properties
X-coordinate value.
Y-coordinate value.
Point is defined as a zero-dimensional
geometry.
The boundary of a Point is the empty set.
A Curve is a one-dimensional geometry,
usually represented by a sequence of points. Particular
subclasses of Curve define the type of
interpolation between points. Curve is a
non-instantiable class.
Curve
Properties
A Curve has the coordinates of its
points.
A Curve is defined as a one-dimensional
geometry.
A Curve is simple if it does not pass
through the same point twice.
A Curve is closed if its start point is
equal to its end point.
The boundary of a closed Curve is empty.
The boundary of a non-closed Curve
consists of its two end points.
A Curve that is simple and closed is a
LinearRing.
A LineString is a Curve
with linear interpolation between points.
LineString
Examples
On a world map, LineString objects could
represent rivers.
In a city map, LineString objects could
represent streets.
LineString
Properties
A LineString has coordinates of segments,
defined by each consecutive pair of points.
A LineString is a Line
if it consists of exactly two points.
A LineString is a
LinearRing if it is both closed and
simple.
A Surface is a two-dimensional geometry. It
is a non-instantiable class. Its only instantiable subclass is
Polygon.
Surface
Properties
A Surface is defined as a two-dimensional
geometry.
The OpenGIS specification defines a simple
Surface as a geometry that consists of a
single “patch” that is associated with a single
exterior boundary and zero or more interior boundaries.
The boundary of a simple Surface is the
set of closed curves corresponding to its exterior and
interior boundaries.
A Polygon is a planar
Surface representing a multisided geometry.
It is defined by a single exterior boundary and zero or more
interior boundaries, where each interior boundary defines a hole
in the Polygon.
Polygon
Examples
On a region map, Polygon objects could
represent forests, districts, an so on.
Polygon
Assertions
The boundary of a Polygon consists of a
set of LinearRing objects (that is,
LineString objects that are both simple
and closed) that make up its exterior and interior
boundaries.
A Polygon has no rings that cross. The
rings in the boundary of a Polygon may
intersect at a Point, but only as a
tangent.
A Polygon has no lines, spikes, or
punctures.
A Polygon has an interior that is a
connected point set.
A Polygon may have holes. The exterior of
a Polygon with holes is not connected.
Each hole defines a connected component of the exterior.
The preceding assertions make a Polygon a
simple geometry.
A GeometryCollection is a geometry that is a
collection of one or more geometries of any class.
All the elements in a GeometryCollection must
be in the same Spatial Reference System (that is, in the same
coordinate system). There are no other constraints on the
elements of a GeometryCollection, although
the subclasses of GeometryCollection
described in the following sections may restrict membership.
Restrictions may be based on:
Element type (for example, a MultiPoint
may contain only Point elements)
Dimension
Constraints on the degree of spatial overlap between elements
A MultiPoint is a geometry collection
composed of Point elements. The points are
not connected or ordered in any way.
MultiPoint
Examples
On a world map, a MultiPoint could
represent a chain of small islands.
On a city map, a MultiPoint could
represent the outlets for a ticket office.
MultiPoint
Properties
A MultiPoint is a zero-dimensional
geometry.
A MultiPoint is simple if no two of its
Point values are equal (have identical
coordinate values).
The boundary of a MultiPoint is the empty
set.
A MultiCurve is a geometry collection
composed of Curve elements.
MultiCurve is a non-instantiable class.
MultiCurve
Properties
A MultiCurve is a one-dimensional
geometry.
A MultiCurve is simple if and only if all
of its elements are simple; the only intersections between
any two elements occur at points that are on the boundaries
of both elements.
A MultiCurve boundary is obtained by
applying the “mod 2 union rule” (also known as
the “odd-even rule”): A point is in the
boundary of a MultiCurve if it is in the
boundaries of an odd number of MultiCurve
elements.
A MultiCurve is closed if all of its
elements are closed.
The boundary of a closed MultiCurve is
always empty.
A MultiLineString is a
MultiCurve geometry collection composed of
LineString elements.
MultiLineString
Examples
On a region map, a MultiLineString could
represent a river system or a highway system.
A MultiSurface is a geometry collection
composed of surface elements. MultiSurface is
a non-instantiable class. Its only instantiable subclass is
MultiPolygon.
MultiSurface
Assertions
Two MultiSurface surfaces have no
interiors that intersect.
Two MultiSurface elements have boundaries
that intersect at most at a finite number of points.
A MultiPolygon is a
MultiSurface object composed of
Polygon elements.
MultiPolygon
Examples
On a region map, a MultiPolygon could
represent a system of lakes.
MultiPolygon
Assertions
A MultiPolygon has no two
Polygon elements with interiors that
intersect.
A MultiPolygon has no two
Polygon elements that cross (crossing is
also forbidden by the previous assertion), or that touch at
an infinite number of points.
A MultiPolygon may not have cut lines,
spikes, or punctures. A MultiPolygon is a
regular, closed point set.
A MultiPolygon that has more than one
Polygon has an interior that is not
connected. The number of connected components of the
interior of a MultiPolygon is equal to
the number of Polygon values in the
MultiPolygon.
MultiPolygon
Properties
A MultiPolygon is a two-dimensional
geometry.
A MultiPolygon boundary is a set of
closed curves (LineString values)
corresponding to the boundaries of its
Polygon elements.
Each Curve in the boundary of the
MultiPolygon is in the boundary of
exactly one Polygon element.
Every Curve in the boundary of an
Polygon element is in the boundary of the
MultiPolygon.
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 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)
Note that point coordinate pairs are separated by commas.
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 grammar that specifies the formal production rules for writing WKT values can be found in the OGC specification document referenced near the beginning of this chapter.
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 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.
This section describes the data types you can use for representing spatial data in MySQL, and the functions available for creating and retrieving spatial values.
MySQL has data types that correspond to OpenGIS classes. Some of these types hold single geometry values:
GEOMETRY
POINT
LINESTRING
POLYGON
GEOMETRY can store geometry values of any
type. The other single-value types, POINT and
LINESTRING and POLYGON,
restrict their values to a particular geometry type.
The other data types hold collections of values:
MULTIPOINT
MULTILINESTRING
MULTIPOLYGON
GEOMETRYCOLLECTION
GEOMETRYCOLLECTION can store a collection of
objects of any type. The other collection types,
MULTIPOINT and
MULTILINESTRING and
MULTIPOLYGON and
GEOMETRYCOLLECTION, restrict collection
members to those having a particular geometry type.
This section describes how to create spatial values using Well-Known Text and Well-Known Binary functions that are defined in the OpenGIS standard, and using MySQL-specific functions.
MySQL provides a number of functions that take as input parameters a Well-Known Text representation and, optionally, a spatial reference system identifier (SRID). They return the corresponding geometry.
GeomFromText() accepts a WKT of any
geometry type as its first argument. An implementation also
provides type-specific construction functions for construction
of geometry values of each geometry type.
GeomCollFromText(
,
wkt[,srid])GeometryCollectionFromText(
wkt[,srid])
Constructs a GEOMETRYCOLLECTION value
using its WKT representation and SRID.
GeomFromText(
,
wkt[,srid])GeometryFromText(
wkt[,srid])
Constructs a geometry value of any type using its WKT representation and SRID.
LineFromText(
,
wkt[,srid])LineStringFromText(
wkt[,srid])
Constructs a LINESTRING value using its
WKT representation and SRID.
MLineFromText(
,
wkt[,srid])MultiLineStringFromText(
wkt[,srid])
Constructs a MULTILINESTRING value
using its WKT representation and SRID.
MPointFromText(
,
wkt[,srid])MultiPointFromText(
wkt[,srid])
Constructs a MULTIPOINT value using its
WKT representation and SRID.
MPolyFromText(
,
wkt[,srid])MultiPolygonFromText(
wkt[,srid])
Constructs a MULTIPOLYGON value using
its WKT representation and SRID.
Constructs a POINT value using its WKT
representation and SRID.
PolyFromText(
,
wkt[,srid])PolygonFromText(
wkt[,srid])
Constructs a POLYGON value using its
WKT representation and SRID.
The OpenGIS specification also describes optional functions
for constructing Polygon or
MultiPolygon values based on the WKT
representation of a collection of rings or closed
LineString values. These values may
intersect. MySQL does not implement these functions:
Constructs a MultiPolygon value from a
MultiLineString value in WKT format
containing an arbitrary collection of closed
LineString values.
Constructs a Polygon value from a
MultiLineString value in WKT format
containing an arbitrary collection of closed
LineString values.
MySQL provides a number of functions that take as input
parameters a BLOB containing a Well-Known
Binary representation and, optionally, a spatial reference
system identifier (SRID). They return the corresponding
geometry.
GeomFromWKB() accepts a WKB of any geometry
type as its first argument. An implementation also provides
type-specific construction functions for construction of
geometry values of each geometry type.
GeomCollFromWKB(
,
wkb[,srid])GeometryCollectionFromWKB(
wkb[,srid])
Constructs a GEOMETRYCOLLECTION value
using its WKB representation and SRID.
GeomFromWKB(
,
wkb[,srid])GeometryFromWKB(
wkb[,srid])
Constructs a geometry value of any type using its WKB representation and SRID.
LineFromWKB(
,
wkb[,srid])LineStringFromWKB(
wkb[,srid])
Constructs a LINESTRING value using its
WKB representation and SRID.
MLineFromWKB(
,
wkb[,srid])MultiLineStringFromWKB(
wkb[,srid])
Constructs a MULTILINESTRING value
using its WKB representation and SRID.
MPointFromWKB(
,
wkb[,srid])MultiPointFromWKB(
wkb[,srid])
Constructs a MULTIPOINT value using its
WKB representation and SRID.
MPolyFromWKB(
,
wkb[,srid])MultiPolygonFromWKB(
wkb[,srid])
Constructs a MULTIPOLYGON value using
its WKB representation and SRID.
Constructs a POINT value using its WKB
representation and SRID.
PolyFromWKB(
,
wkb[,srid])PolygonFromWKB(
wkb[,srid])
Constructs a POLYGON value using its
WKB representation and SRID.
The OpenGIS specification also describes optional functions
for constructing Polygon or
MultiPolygon values based on the WKB
representation of a collection of rings or closed
LineString values. These values may
intersect. MySQL does not implement these functions:
Constructs a MultiPolygon value from a
MultiLineString value in WKB format
containing an arbitrary collection of closed
LineString values.
Constructs a Polygon value from a
MultiLineString value in WKB format
containing an arbitrary collection of closed
LineString values.
Note: MySQL does not implement the functions listed in this section.
MySQL provides a set of useful functions for creating geometry
WKB representations. The functions described in this section
are MySQL extensions to the OpenGIS specifications. The
results of these functions are BLOB values
containing WKB representations of geometry values with no
SRID. The results of these functions can be substituted as the
first argument for any function in the
GeomFromWKB() function family.
Constructs a WKB GeometryCollection. If
any argument is not a well-formed WKB representation of a
geometry, the return value is NULL.
Constructs a WKB LineString value from
a number of WKB Point arguments. If any
argument is not a WKB Point, the return
value is NULL. If the number of
Point arguments is less than two, the
return value is NULL.
Constructs a WKB MultiLineString value
using WKB LineString arguments. If any
argument is not a WKB LineString, the
return value is NULL.
Constructs a WKB MultiPoint value using
WKB Point arguments. If any argument is
not a WKB Point, the return value is
NULL.
Constructs a WKB MultiPolygon value
from a set of WKB Polygon arguments. If
any argument is not a WKB Polygon, the
return value is NULL.
Constructs a WKB Point using its
coordinates.
Constructs a WKB Polygon value from a
number of WKB LineString arguments. If
any argument does not represent the WKB of a
LinearRing (that is, not a closed and
simple LineString) the return value is
NULL.
MySQL provides a standard way of creating spatial columns for
geometry types, for example, with CREATE
TABLE or ALTER TABLE. Currently,
spatial columns are supported only for MyISAM
tables.
Use the CREATE TABLE statement to create
a table with a spatial column:
mysql> CREATE TABLE geom (g GEOMETRY);
Query OK, 0 rows affected (0.02 sec)
Use the ALTER TABLE statement to add or
drop a spatial column to or from an existing table:
mysql>ALTER TABLE geom ADD pt POINT;Query OK, 0 rows affected (0.00 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql>ALTER TABLE geom DROP pt;Query OK, 0 rows affected (0.00 sec) Records: 0 Duplicates: 0 Warnings: 0
After you have created spatial columns, you can populate them with spatial data.
Values should be stored in internal geometry format, but you can convert them to that format from either Well-Known Text (WKT) or Well-Known Binary (WKB) format. The following examples demonstrate how to insert geometry values into a table by converting WKT values into internal geometry format.
You can perform the conversion directly in the
INSERT statement:
INSERT INTO geom VALUES (GeomFromText('POINT(1 1)'));
SET @g = 'POINT(1 1)';
INSERT INTO geom VALUES (GeomFromText(@g));
Or you can perform the conversion prior to the
INSERT:
SET @g = GeomFromText('POINT(1 1)');
INSERT INTO geom VALUES (@g);
The following examples insert more complex geometries into the table:
SET @g = 'LINESTRING(0 0,1 1,2 2)'; INSERT INTO geom VALUES (GeomFromText(@g)); SET @g = 'POLYGON((0 0,10 0,10 10,0 10,0 0),(5 5,7 5,7 7,5 7, 5 5))'; INSERT INTO geom VALUES (GeomFromText(@g)); SET @g = 'GEOMETRYCOLLECTION(POINT(1 1),LINESTRING(0 0,1 1,2 2,3 3,4 4))'; INSERT INTO geom VALUES (GeomFromText(@g));
The preceding examples all use GeomFromText()
to create geometry values. You can also use type-specific
functions:
SET @g = 'POINT(1 1)'; INSERT INTO geom VALUES (PointFromText(@g)); SET @g = 'LINESTRING(0 0,1 1,2 2)'; INSERT INTO geom VALUES (LineStringFromText(@g)); SET @g = 'POLYGON((0 0,10 0,10 10,0 10,0 0),(5 5,7 5,7 7,5 7, 5 5))'; INSERT INTO geom VALUES (PolygonFromText(@g)); SET @g = 'GEOMETRYCOLLECTION(POINT(1 1),LINESTRING(0 0,1 1,2 2,3 3,4 4))'; INSERT INTO geom VALUES (GeomCollFromText(@g));
Note that if a client application program wants to use WKB representations of geometry values, it is responsible for sending correctly formed WKB in queries to the server. However, there are several ways of satisfying this requirement. For example:
Inserting a POINT(1 1) value with hex
literal syntax:
mysql>INSERT INTO geom VALUES->(GeomFromWKB(0x0101000000000000000000F03F000000000000F03F));
An ODBC application can send a WKB representation, binding
it to a placeholder using an argument of
BLOB type:
INSERT INTO geom VALUES (GeomFromWKB(?))
Other programming interfaces may support a similar placeholder mechanism.
In a C program, you can escape a binary value using
mysql_real_escape_string() and include
the result in a query string that is sent to the server. See
Section 23.2.3.52, “mysql_real_escape_string()”.
Geometry values stored in a table can be fetched in internal format. You can also convert them into WKT or WKB format.
Fetching geometry values using internal format can be useful in table-to-table transfers:
CREATE TABLE geom2 (g GEOMETRY) SELECT g FROM geom;
The AsText() function converts a geometry
from internal format into a WKT string.
mysql> SELECT AsText(g) FROM geom;
+-------------------------+
| AsText(p1) |
+-------------------------+
| POINT(1 1) |
| LINESTRING(0 0,1 1,2 2) |
+-------------------------+
Geometry FunctionsAfter populating spatial columns with values, you are ready to query and analyze them. MySQL provides a set of functions to perform various operations on spatial data. These functions can be grouped into four major categories according to the type of operation they perform:
Functions that convert geometries between various formats
Functions that provide access to qualitative or quantitative properties of a geometry
Functions that describe relations between two geometries
Functions that create new geometries from existing ones
Spatial analysis functions can be used in many contexts, such as:
Any interactive SQL program, such as mysql or MySQLCC
Application programs written in any language that supports a MySQL client API
MySQL supports the following functions for converting geometry values between internal format and either WKT or WKB format:
Converts a value in internal geometry format to its WKB representation and returns the binary result.
Converts a value in internal geometry format to its WKT representation and returns the string result.
mysql>SET @g = 'LineString(1 1,2 2,3 3)';mysql>SELECT AsText(GeomFromText(@g));+--------------------------+ | AsText(GeomFromText(@G)) | +--------------------------+ | LINESTRING(1 1,2 2,3 3) | +--------------------------+
Converts a string value from its WKT representation into
internal geometry format and returns the result. A number of
type-specific functions are also supported, such as
PointFromText() and
LineFromText(); see
Section 17.4.2.1, “Creating Geometry Values Using WKT Functions”.
Converts a binary value from its WKB representation into
internal geometry format and returns the result. A number of
type-specific functions are also supported, such as
PointFromWKB() and
LineFromWKB(); see
Section 17.4.2.2, “Creating Geometry Values Using WKB Functions”.
Each function that belongs to this group takes a geometry value
as its argument and returns some quantitative or qualitative
property of the geometry. Some functions restrict their argument
type. Such functions return NULL if the
argument is of an incorrect geometry type. For example,
Area() returns NULL if the
object type is neither Polygon nor
MultiPolygon.
The functions listed in this section do not restrict their argument and accept a geometry value of any type.
Returns the inherent dimension of the geometry value
g. The result can be −1, 0,
1, or 2. (The meaning of these values is given in
Section 17.2.2, “Class Geometry”.)
mysql> SELECT Dimension(GeomFromText('LineString(1 1,2 2)'));
+------------------------------------------------+
| Dimension(GeomFromText('LineString(1 1,2 2)')) |
+------------------------------------------------+
| 1 |
+------------------------------------------------+
Returns the Minimum Bounding Rectangle (MBR) for the
geometry value g. The result is
returned as a Polygon value.
The polygon is defined by the corner points of the bounding box:
POLYGON((MINX MINY, MAXX MINY, MAXX MAXY, MINX MAXY, MINX MINY))
mysql> SELECT AsText(Envelope(GeomFromText('LineString(1 1,2 2)')));
+-------------------------------------------------------+
| AsText(Envelope(GeomFromText('LineString(1 1,2 2)'))) |
+-------------------------------------------------------+
| POLYGON((1 1,2 1,2 2,1 2,1 1)) |
+-------------------------------------------------------+
Returns as a string the name of the geometry type of which
the geometry instance g is a
member. The name corresponds to one of the instantiable
Geometry subclasses.
mysql> SELECT GeometryType(GeomFromText('POINT(1 1)'));
+------------------------------------------+
| GeometryType(GeomFromText('POINT(1 1)')) |
+------------------------------------------+
| POINT |
+------------------------------------------+
Returns an integer indicating the Spatial Reference System
ID for the geometry value g.
In MySQL, the SRID value is just an integer associated with the geometry value. All calculations are done assuming Euclidean (planar) geometry.
mysql> SELECT SRID(GeomFromText('LineString(1 1,2 2)',101));
+-----------------------------------------------+
| SRID(GeomFromText('LineString(1 1,2 2)',101)) |
+-----------------------------------------------+
| 101 |
+-----------------------------------------------+
The OpenGIS specification also defines the following functions, which MySQL does not implement:
Returns a geometry that is the closure of the
combinatorial boundary of the geometry value
g.
Returns 1 if the geometry value
g is the empty geometry, 0 if
it is not empty, and −1 if the argument is
NULL. If the geometry is empty, it
represents the empty point set.
Currently, this function is a placeholder and should not be used. If implemented, its behavior will be as described in the next paragraph.
Returns 1 if the geometry value
g has no anomalous geometric
points, such as self-intersection or self-tangency.
IsSimple() returns 0 if the argument is
not simple, and −1 if it is NULL.
The description of each instantiable geometric class given earlier in the chapter includes the specific conditions that cause an instance of that class to be classified as not simple.
A Point consists of X and Y coordinates,
which may be obtained using the following functions:
Returns the X-coordinate value for the point
p as a double-precision number.
mysql> SELECT X(GeomFromText('Point(56.7 53.34)'));
+--------------------------------------+
| X(GeomFromText('Point(56.7 53.34)')) |
+--------------------------------------+
| 56.7 |
+--------------------------------------+
Returns the Y-coordinate value for the point
p as a double-precision number.
mysql> SELECT Y(GeomFromText('Point(56.7 53.34)'));
+--------------------------------------+
| Y(GeomFromText('Point(56.7 53.34)')) |
+--------------------------------------+
| 53.34 |
+--------------------------------------+
A LineString consists of
Point values. You can extract particular
points of a LineString, count the number of
points that it contains, or obtain its length.
Returns the Point that is the end point
of the LineString value
ls.
mysql>SET @ls = 'LineString(1 1,2 2,3 3)';mysql>SELECT AsText(EndPoint(GeomFromText(@ls)));+-------------------------------------+ | AsText(EndPoint(GeomFromText(@ls))) | +-------------------------------------+ | POINT(3 3) | +-------------------------------------+
Returns as a double-precision number the length of the
LineString value
ls in its associated spatial
reference.
mysql>SET @ls = 'LineString(1 1,2 2,3 3)';mysql>SELECT GLength(GeomFromText(@ls));+----------------------------+ | GLength(GeomFromText(@ls)) | +----------------------------+ | 2.8284271247462 | +----------------------------+
Returns the number of points in the
LineString value
ls.
mysql>SET @ls = 'LineString(1 1,2 2,3 3)';mysql>SELECT NumPoints(GeomFromText(@ls));+------------------------------+ | NumPoints(GeomFromText(@ls)) | +------------------------------+ | 3 | +------------------------------+
Returns the n-th point in the
Linestring value
ls. Point numbers begin at 1.
mysql>SET @ls = 'LineString(1 1,2 2,3 3)';mysql>SELECT AsText(PointN(GeomFromText(@ls),2));+-------------------------------------+ | AsText(PointN(GeomFromText(@ls),2)) | +-------------------------------------+ | POINT(2 2) | +-------------------------------------+
Returns the Point that is the start
point of the LineString value
ls.
mysql>SET @ls = 'LineString(1 1,2 2,3 3)';mysql>SELECT AsText(StartPoint(GeomFromText(@ls)));+---------------------------------------+ | AsText(StartPoint(GeomFromText(@ls))) | +---------------------------------------+ | POINT(1 1) | +---------------------------------------+
The OpenGIS specification also defines the following function, which MySQL does not implement:
Returns as a double-precision number the length of the
MultiLineString value
mls. The length of
mls is equal to the sum of the
lengths of its elements.
mysql>SET @mls = 'MultiLineString((1 1,2 2,3 3),(4 4,5 5))';mysql>SELECT GLength(GeomFromText(@mls));+-----------------------------+ | GLength(GeomFromText(@mls)) | +-----------------------------+ | 4.2426406871193 | +-----------------------------+
Returns 1 if the MultiLineString value
mls is closed (that is, the
StartPoint() and
EndPoint() values are the same for each
LineString in
mls). Returns 0 if
mls is not closed, and −1 if
it is NULL.
mysql>SET @mls = 'MultiLineString((1 1,2 2,3 3),(4 4,5 5))';mysql>SELECT IsClosed(GeomFromText(@mls));+------------------------------+ | IsClosed(GeomFromText(@mls)) | +------------------------------+ | 0 | +------------------------------+
Returns as a double-precision number the area of the
Polygon value
poly, as measured in its
spatial reference system.
mysql>SET @poly = 'Polygon((0 0,0 3,3 0,0 0),(1 1,1 2,2 1,1 1))';mysql>SELECT Area(GeomFromText(@poly));+---------------------------+ | Area(GeomFromText(@poly)) | +---------------------------+ | 4 | +---------------------------+
Returns the exterior ring of the
Polygon value
poly as a
LineString.
mysql>SET @poly =->'Polygon((0 0,0 3,3 3,3 0,0 0),(1 1,1 2,2 2,2 1,1 1))';mysql>SELECT AsText(ExteriorRing(GeomFromText(@poly)));+-------------------------------------------+ | AsText(ExteriorRing(GeomFromText(@poly))) | +-------------------------------------------+ | LINESTRING(0 0,0 3,3 3,3 0,0 0) | +-------------------------------------------+
Returns the n-th interior ring
for the Polygon value
poly as a
LineString. Ring numbers begin at 1.
mysql>SET @poly =->'Polygon((0 0,0 3,3 3,3 0,0 0),(1 1,1 2,2 2,2 1,1 1))';mysql>SELECT AsText(InteriorRingN(GeomFromText(@poly),1));+----------------------------------------------+ | AsText(InteriorRingN(GeomFromText(@poly),1)) | +----------------------------------------------+ | LINESTRING(1 1,1 2,2 2,2 1,1 1) | +----------------------------------------------+
Returns the number of interior rings in the
Polygon value
poly.
mysql>SET @poly =->'Polygon((0 0,0 3,3 3,3 0,0 0),(1 1,1 2,2 2,2 1,1 1))';mysql>SELECT NumInteriorRings(GeomFromText(@poly));+---------------------------------------+ | NumInteriorRings(GeomFromText(@poly)) | +---------------------------------------+ | 1 | +---------------------------------------+
Returns as a double-precision number the area of the
MultiPolygon value
mpoly, as measured in its
spatial reference system.
mysql>SET @mpoly =->'MultiPolygon(((0 0,0 3,3 3,3 0,0 0),(1 1,1 2,2 2,2 1,1 1)))';mysql>SELECT Area(GeomFromText(@mpoly));+----------------------------+ | Area(GeomFromText(@mpoly)) | +----------------------------+ | 8 | +----------------------------+
The OpenGIS specification also defines the following functions, which MySQL does not implement:
Returns the n-th geometry in
the GeometryCollection value
gc. Geometry numbers begin at
1.
mysql>SET @gc = 'GeometryCollection(Point(1 1),LineString(2 2, 3 3))';mysql>SELECT AsText(GeometryN(GeomFromText(@gc),1));+----------------------------------------+ | AsText(GeometryN(GeomFromText(@gc),1)) | +----------------------------------------+ | POINT(1 1) | +----------------------------------------+
Returns the number of geometries in the
GeometryCollection value
gc.
mysql>SET @gc = 'GeometryCollection(Point(1 1),LineString(2 2, 3 3))';mysql>SELECT NumGeometries(GeomFromText(@gc));+----------------------------------+ | NumGeometries(GeomFromText(@gc)) | +----------------------------------+ | 2 | +----------------------------------+
In the section Section 17.5.2, “Geometry Functions”,
we've discussed some functions that can construct new
geometries from the existing ones:
Envelope(
g)
StartPoint(
ls)
EndPoint(
ls)
PointN(
ls,n)
ExteriorRing(
poly)
InteriorRingN(
poly,n)
GeometryN(
gc,n)
OpenGIS proposes a number of other functions that can produce geometries. They are designed to implement spatial operators.
These functions are not implemented in MySQL. They may appear in future releases.
Returns a geometry that represents all points whose
distance from the geometry value
g is less than or equal to a
distance of d.
Returns a geometry that represents the convex hull of the
geometry value g.
Returns a geometry that represents the point set
difference of the geometry value
g1 with
g2.
Returns a geometry that represents the point set
intersection of the geometry values
g1 with
g2.
Returns a geometry that represents the point set symmetric
difference of the geometry value
g1 with
g2.
Returns a geometry that represents the point set union of
the geometry values g1 and
g2.
The functions described in these sections take two geometries as input parameters and return a qualitative or quantitative relation between them.
MySQL provides some functions that can test relations between
minimal bounding rectangles of two geometries
g1 and g2. They include:
Returns 1 or 0 to indicate whether or not the Minimum
Bounding Rectangle of g1 contains
the Minimum Bounding Rectangle of
g2.
mysql>SET @g1 = GeomFromText('Polygon((0 0,0 3,3 3,3 0,0 0))');mysql>SET @g2 = GeomFromText('Point(1 1)');mysql>SELECT MBRContains(@g1,@g2), MBRContains(@g2,@g1);----------------------+----------------------+ | MBRContains(@g1,@g2) | MBRContains(@g2,@g1) | +----------------------+----------------------+ | 1 | 0 | +----------------------+----------------------+
Returns 1 or 0 to indicate whether or not the Minimum
Bounding Rectangles of the two geometries
g1 and
g2 are disjoint (do not
intersect).
Returns 1 or 0 to indicate whether or not the Minimum
Bounding Rectangles of the two geometries
g1 and
g2 are the same.
Returns 1 or 0 to indicate whether or not the Minimum
Bounding Rectangles of the two geometries
g1 and
g2 intersect.
Returns 1 or 0 to indicate whether or not the Minimum
Bounding Rectangles of the two geometries
g1 and
g2 overlap.
Returns 1 or 0 to indicate whether or not the Minimum
Bounding Rectangles of the two geometries
g1 and
g2 touch.
Returns 1 or 0 to indicate whether or not the Minimum
Bounding Rectangle of g1 is
within the Minimum Bounding Rectangle of
g2.
mysql>SET @g1 = GeomFromText('Polygon((0 0,0 3,3 3,3 0,0 0))');mysql>SET @g2 = GeomFromText('Polygon((0 0,0 5,5 5,5 0,0 0))');mysql>SELECT MBRWithin(@g1,@g2), MBRWithin(@g2,@g1);+--------------------+--------------------+ | MBRWithin(@g1,@g2) | MBRWithin(@g2,@g1) | +--------------------+--------------------+ | 1 | 0 | +--------------------+--------------------+
The OpenGIS specification defines the following functions.
Currently, MySQL does not implement them according to the
specification. Those that are implemented return the same result
as the corresponding MBR-based functions. This includes
functions in the following list other than
Distance() and Related().
These functions may be implemented in future releases with full support for spatial analysis, not just MBR-based support.
The functions operate on two geometry values
g1 and g2.
Returns 1 or 0 to indicate whether or not
g1 completely contains
g2.
Returns 1 if g1 spatially crosses
g2. Returns
NULL if g1 is a
Polygon or a
MultiPolygon, or if
g2 is a Point
or a MultiPoint. Otherwise, returns 0.
The term spatially crosses denotes a spatial relation between two given geometries that has the following properties:
The two geometries intersect
Their intersection results in a geometry that has a dimension that is one less than the maximum dimension of the two given geometries
Their intersection is not equal to either of the two given geometries
Returns 1 or 0 to indicate whether or not
g1 is spatially disjoint from
(does not intersect) g2.
Returns as a double-precision number the shortest distance between any two points in the two geometries.
Returns 1 or 0 to indicate whether or not
g1 is spatially equal to
g2.
Returns 1 or 0 to indicate whether or not
g1 spatially intersects
g2.
Returns 1 or 0 to indicate whether or not
g1 spatially overlaps
g2. The term spatially
overlaps is used if two geometries intersect and
their intersection results in a geometry of the same
dimension but not equal to either of the given geometries.
Returns 1 or 0 to indicate whether or not the spatial
relationship specified by
pattern_matrix exists between
g1 and
g2. Returns −1 if the arguments
are NULL. The pattern matrix is a string.
Its specification will be noted here if this function is
implemented.
Returns 1 or 0 to indicate whether or not
g1 spatially touches
g2. Two geometries
spatially touch if the interiors of the
geometries do not intersect, but the boundary of one of the
geometries intersects either the boundary or the interior of
the other.
Returns 1 or 0 to indicate whether or not
g1 is spatially within
g2.
Search operations in non-spatial databases can be optimized using indexes. This is true for spatial databases as well. With the help of a great variety of multi-dimensional indexing methods that have previously been designed, it is possible to optimize spatial searches. The most typical of these are:
Point queries that search for all objects that contain a given point
Region queries that search for all objects that overlap a given region
MySQL uses R-Trees with quadratic splitting to index spatial columns. A spatial index is built using the MBR of a geometry. For most geometries, the MBR is a minimum rectangle that surrounds the geometries. For a horizontal or a vertical linestring, the MBR is a rectangle degenerated into the linestring. For a point, the MBR is a rectangle degenerated into the point.
It is also possible to create normal indexes on spatial columns.
Beginning with MySQL 5.0.16, you must declare a prefix for any
(non-spatial) index on a spatial column excepting
POINT columns.
MySQL can create spatial indexes using syntax similar to that
for creating regular indexes, but extended with the
SPATIAL keyword. Spatial columns that are
indexed currently must be declared NOT NULL.
The following examples demonstrate how to create spatial
indexes.
With CREATE TABLE:
mysql> CREATE TABLE geom (g GEOMETRY NOT NULL, SPATIAL INDEX(g));
With ALTER TABLE:
mysql> ALTER TABLE geom ADD SPATIAL INDEX(g);
With CREATE INDEX:
mysql> CREATE SPATIAL INDEX sp_index ON geom (g);
For MyISAM tables, SPATIAL
INDEX creates an R-tree index. For other storage
engines that support spatial index, SPATIAL
INDEX creates a B-tree index. A B-tree index on
spatial values will be useful for exact-value lookups, but not
for range scans.
To drop spatial indexes, use ALTER TABLE or
DROP INDEX:
With ALTER TABLE:
mysql> ALTER TABLE geom DROP INDEX g;
With DROP INDEX:
mysql> DROP INDEX sp_index ON geom;
Example: Suppose that a table geom contains
more than 32,000 geometries, which are stored in the column
g of type GEOMETRY. The
table also has an AUTO_INCREMENT column
fid for storing object ID values.
mysql>DESCRIBE geom;+-------+----------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-------+----------+------+-----+---------+----------------+ | fid | int(11) | | PRI | NULL | auto_increment | | g | geometry | | | | | +-------+----------+------+-----+---------+----------------+ 2 rows in set (0.00 sec) mysql>SELECT COUNT(*) FROM geom;+----------+ | count(*) | +----------+ | 32376 | +----------+ 1 row in set (0.00 sec)
To add a spatial index on the column g, use
this statement:
mysql> ALTER TABLE geom ADD SPATIAL INDEX(g);
Query OK, 32376 rows affected (4.05 sec)
Records: 32376 Duplicates: 0 Warnings: 0
The optimizer investigates whether available spatial indexes can
be involved in the search for queries that use a function such
as MBRContains() or
MBRWithin() in the WHERE
clause. For example, let's say we want to find all objects that
are in the given rectangle:
mysql>SELECT fid,AsText(g) FROM geom WHEREmysql>MBRContains(GeomFromText('Polygon((30000 15000,31000 15000,31000 16000,30000 16000,30000 15000))'),g);+-----+-----------------------------------------------------------------------------+ | fid | AsText(g) | +-----+-----------------------------------------------------------------------------+ | 21 | LINESTRING(30350.4 15828.8,30350.6 15845,30333.8 15845,30333.8 15828.8) | | 22 | LINESTRING(30350.6 15871.4,30350.6 15887.8,30334 15887.8,30334 15871.4) | | 23 | LINESTRING(30350.6 15914.2,30350.6 15930.4,30334 15930.4,30334 15914.2) | | 24 | LINESTRING(30290.2 15823,30290.2 15839.4,30273.4 15839.4,30273.4 15823) | | 25 | LINESTRING(30291.4 15866.2,30291.6 15882.4,30274.8 15882.4,30274.8 15866.2) | | 26 | LINESTRING(30291.6 15918.2,30291.6 15934.4,30275 15934.4,30275 15918.2) | | 249 | LINESTRING(30337.8 15938.6,30337.8 15946.8,30320.4 15946.8,30320.4 15938.4) | | 1 | LINESTRING(30250.4 15129.2,30248.8 15138.4,30238.2 15136.4,30240 15127.2) | | 2 | LINESTRING(30220.2 15122.8,30217.2 15137.8,30207.6 15136,30210.4 15121) | | 3 | LINESTRING(30179 15114.4,30176.6 15129.4,30167 15128,30169 15113) | | 4 | LINESTRING(30155.2 15121.4,30140.4 15118.6,30142 15109,30157 15111.6) | | 5 | LINESTRING(30192.4 15085,30177.6 15082.2,30179.2 15072.4,30194.2 15075.2) | | 6 | LINESTRING(30244 15087,30229 15086.2,30229.4 15076.4,30244.6 15077) | | 7 | LINESTRING(30200.6 15059.4,30185.6 15058.6,30186 15048.8,30201.2 15049.4) | | 10 | LINESTRING(30179.6 15017.8,30181 15002.8,30190.8 15003.6,30189.6 15019) | | 11 | LINESTRING(30154.2 15000.4,30168.6 15004.8,30166 15014.2,30151.2 15009.8) | | 13 | LINESTRING(30105 15065.8,30108.4 15050.8,30118 15053,30114.6 15067.8) | | 154 | LINESTRING(30276.2 15143.8,30261.4 15141,30263 15131.4,30278 15134) | | 155 | LINESTRING(30269.8 15084,30269.4 15093.4,30258.6 15093,30259 15083.4) | | 157 | LINESTRING(30128.2 15011,30113.2 15010.2,30113.6 15000.4,30128.8 15001) | +-----+-----------------------------------------------------------------------------+ 20 rows in set (0.00 sec)
Let's use EXPLAIN to check the way this query
is executed (the id column has been removed
so the output better fits the page):
mysql>EXPLAIN SELECT fid,AsText(g) FROM geom WHEREmysql>MBRContains(GeomFromText('Polygon((30000 15000,31000 15000,31000 16000,30000 16000,30000 15000))'),g);+-------------+-------+-------+---------------+------+---------+------+------+-------------+ | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +-------------+-------+-------+---------------+------+---------+------+------+-------------+ | SIMPLE | geom | range | g | g | 32 | NULL | 50 | Using where | +-------------+-------+-------+---------------+------+---------+------+------+-------------+ 1 row in set (0.00 sec)
Let's check what would happen without a spatial index:
mysql>EXPLAIN SELECT fid,AsText(g) FROM g IGNORE INDEX (g) WHEREmysql>MBRContains(GeomFromText('Polygon((30000 15000,31000 15000,31000 16000,30000 16000,30000 15000))'),g);+-------------+-------+------+---------------+------+---------+------+-------+-------------+ | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +-------------+-------+------+---------------+------+---------+------+-------+-------------+ | SIMPLE | geom | ALL | NULL | NULL | NULL | NULL | 32376 | Using where | +-------------+-------+------+---------------+------+---------+------+-------+-------------+ 1 row in set (0.00 sec)
Let's execute the SELECT statement, ignoring
the spatial key we have:
mysql>SELECT fid,AsText(g) FROM geom IGNORE INDEX (g) WHEREmysql>MBRContains(GeomFromText('Polygon((30000 15000,31000 15000,31000 16000,30000 16000,30000 15000))'),g);+-----+-----------------------------------------------------------------------------+ | fid | AsText(g) | +-----+-----------------------------------------------------------------------------+ | 1 | LINESTRING(30250.4 15129.2,30248.8 15138.4,30238.2 15136.4,30240 15127.2) | | 2 | LINESTRING(30220.2 15122.8,30217.2 15137.8,30207.6 15136,30210.4 15121) | | 3 | LINESTRING(30179 15114.4,30176.6 15129.4,30167 15128,30169 15113) | | 4 | LINESTRING(30155.2 15121.4,30140.4 15118.6,30142 15109,30157 15111.6) | | 5 | LINESTRING(30192.4 15085,30177.6 15082.2,30179.2 15072.4,30194.2 15075.2) | | 6 | LINESTRING(30244 15087,30229 15086.2,30229.4 15076.4,30244.6 15077) | | 7 | LINESTRING(30200.6 15059.4,30185.6 15058.6,30186 15048.8,30201.2 15049.4) | | 10 | LINESTRING(30179.6 15017.8,30181 15002.8,30190.8 15003.6,30189.6 15019) | | 11 | LINESTRING(30154.2 15000.4,30168.6 15004.8,30166 15014.2,30151.2 15009.8) | | 13 | LINESTRING(30105 15065.8,30108.4 15050.8,30118 15053,30114.6 15067.8) | | 21 | LINESTRING(30350.4 15828.8,30350.6 15845,30333.8 15845,30333.8 15828.8) | | 22 | LINESTRING(30350.6 15871.4,30350.6 15887.8,30334 15887.8,30334 15871.4) | | 23 | LINESTRING(30350.6 15914.2,30350.6 15930.4,30334 15930.4,30334 15914.2) | | 24 | LINESTRING(30290.2 15823,30290.2 15839.4,30273.4 15839.4,30273.4 15823) | | 25 | LINESTRING(30291.4 15866.2,30291.6 15882.4,30274.8 15882.4,30274.8 15866.2) | | 26 | LINESTRING(30291.6 15918.2,30291.6 15934.4,30275 15934.4,30275 15918.2) | | 154 | LINESTRING(30276.2 15143.8,30261.4 15141,30263 15131.4,30278 15134) | | 155 | LINESTRING(30269.8 15084,30269.4 15093.4,30258.6 15093,30259 15083.4) | | 157 | LINESTRING(30128.2 15011,30113.2 15010.2,30113.6 15000.4,30128.8 15001) | | 249 | LINESTRING(30337.8 15938.6,30337.8 15946.8,30320.4 15946.8,30320.4 15938.4) | +-----+-----------------------------------------------------------------------------+ 20 rows in set (0.46 sec)
When the index is not used, the execution time for this query rises from 0.00 seconds to 0.46 seconds.
In future releases, spatial indexes may also be used for optimizing other functions. See Section 17.5.4, “Functions for Testing Spatial Relations Between Geometric Objects”.
Additional Metadata Views
OpenGIS specifications propose several additional metadata
views. For example, a system view named
GEOMETRY_COLUMNS contains a description
of geometry columns, one row for each geometry column in the
database.
The OpenGIS function Length() on
LineString and
MultiLineString currently should be
called in MySQL as GLength()
The problem is that there is an existing SQL function
Length() which calculates the length of
string values, and sometimes it is not possible to
distinguish whether the function is called in a textual or
spatial context. We need either to solve this somehow, or
decide on another function name.