Oracle 5.0, Справочное руководство

Страница: 1003 / 3232

Supported Spatial Data Formats
983
12.16.3. 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.
12.16.3.1. Well-Known Text (WKT) Format
The Well-Known Text (WKT) representation of Geometry is designed to exchange geometry data in
ASCII form. For a Backus-Naur grammar that specifies the formal production rules for writing WKT
values, see the OpenGIS specification document referenced in
Section 12.16, “Spatial Extensions” .
Examples of WKT representations of geometry objects:
• A
Point
:
POINT(15 20)
Note that point coordinates are specified with no separating comma. This differs from the syntax for
the SQL
POINT()
[987] function, which requires a comma between the coordinates. Take care
to use the syntax appropriate to the context of a given spatial operation. For example, the following
statements both extract the X-coordinate from a
Point
object. The first produces the object directly
using the
POINT()
[987] function. The second uses a WKT representation converted to a
Point
with
GeomFromText()
.
mysql> SELECT X(POINT(15, 20));
+------------------+
| X(POINT(15, 20)) |
+------------------+
| 15 |
+------------------+
mysql> SELECT X(GeomFromText('POINT(15 20)'));
+---------------------------------+
| X(GeomFromText('POINT(15 20)')) |
+---------------------------------+
| 15 |
+---------------------------------+
• 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)))