Oracle 5.0, Reference Manual

Page: 1013 / 3232

Spatial Analysis Functions
993
+-------------------------------------+
•
StartPoint(ls)
[993]
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:
•
IsRing(ls)
[993]
Returns 1 if the
LineString
value
ls
is closed (that is, its
StartPoint()
[993] and
EndPoint()
[992] values are the same) and is simple (does not pass through the same point
more than once). Returns 0 if
ls
is not a ring, and –1 if it is
NULL
.
12.16.5.2.4.
MultiLineString
Functions
These functions return properties of
MultiLineString
values.
•
GLength(mls)
[992]
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 |
+-----------------------------+
GLength()
[992] is a nonstandard name. It corresponds to the OpenGIS
Length()
[890]
function.
•
IsClosed(mls)
[993]
Returns 1 if the
MultiLineString
value
mls
is closed (that is, the
StartPoint()
[993] and
EndPoint()
[992] 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 |
+------------------------------+
12.16.5.2.5.
Polygon
Functions
These functions return properties of
Polygon
values.
•
Area(poly)
[993]
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));