Oracle 5.0, Reference Manual

Page: 1015 / 3232

Spatial Analysis Functions
995
mysql> SET @poly =
-> GeomFromText('POLYGON((0 0,10 0,10 10,0 10,0 0),(5 5,7 5,7 7,5 7,5 5))');
mysql> SELECT GeometryType(@poly),AsText(Centroid(@poly));
+---------------------+--------------------------------------------+
| GeometryType(@poly) | AsText(Centroid(@poly)) |
+---------------------+--------------------------------------------+
| POLYGON | POINT(4.958333333333333 4.958333333333333) |
+---------------------+--------------------------------------------+
The OpenGIS specification also defines the following function, which MySQL does not implement:
•
PointOnSurface(mpoly)
Returns a
Point
value that is guaranteed to be on the
MultiPolygon
value
mpoly
.
12.16.5.2.7.
GeometryCollection
Functions
These functions return properties of
GeometryCollection
values.
•
GeometryN(gc,N)
[995]
Returns the
N
-th geometry in the
GeometryCollection
value
gc
. Geometries are numbered
beginning with 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) |
+----------------------------------------+
•
NumGeometries(gc)
[995]
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 |
+----------------------------------+
12.16.5.3. Functions That Create New Geometries from Existing Ones
The following sections describe functions that take geometry values as arguments and return new
geometry values.
12.16.5.3.1. Geometry Functions That Produce New Geometries
Section 12.16.5.2, “
Geometry
Property Functions” , discusses several functions that construct new
geometries from existing ones. See that section for descriptions of these functions:
•
Envelope(g)
[990]
•
StartPoint(ls)
[993]
•
EndPoint(ls)
[992]
•
PointN(ls,N)
[992]
•
ExteriorRing(poly)
[994]
•
InteriorRingN(poly,N)
[994]