11.5.2.3 LineString Property Analysis Functions

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.

EndPoint(ls)

Returns the Point that is the end point of the LineString value ls.

mysql> SELECT AsText(EndPoint(GeomFromText('LineString(1 1,2 2,3 3)')));
+------------------------------------------------------------+
| AsText(EndPoint(GeomFromText('LineString(1 1,2 2,3 3)')))  |
+------------------------------------------------------------+
| POINT(3 3)                                                 |
+------------------------------------------------------------+

GLength(ls)

Returns as a double-precision number the length of the LineString value ls in its associated spatial reference.

mysql> SELECT GLength(GeomFromText('LineString(1 1,2 2,3 3)'));
+--------------------------------------------------+
| GLength(GeomFromText('LineString(1 1,2 2,3 3)')) |
+--------------------------------------------------+
|                                  2.8284271247462 |
+--------------------------------------------------+

IsClosed(ls)

Returns 1 if the LineString value ls is closed (that is, it sStartPoint() and EndPoint() values are the same). Returns 0 if ls is not closed, and -1 if it is NULL.

mysql> SELECT IsClosed(GeomFromText('LineString(1 1,2 2,3 3)'));
+---------------------------------------------------+
| IsClosed(GeomFromText('LineString(1 1,2 2,3 3)')) |
+---------------------------------------------------+
|                                                 0 |
+---------------------------------------------------+

NumPoints(ls)

Returns the number of points in the LineString value ls.

mysql> SELECT NumPoints(GeomFromText('LineString(1 1,2 2,3 3)'));
+----------------------------------------------------+
| NumPoints(GeomFromText('LineString(1 1,2 2,3 3)')) |
+----------------------------------------------------+
|                                                  3 |
+----------------------------------------------------+

PointN(ls,n)

Returns the n-th point in the Linestring value ls. Point numbers begin at 1.

mysql> SELECT AsText(PointN(GeomFromText('LineString(1 1,2 2,3 3)'),2));
+-----------------------------------------------------------+
| AsText(PointN(GeomFromText('LineString(1 1,2 2,3 3)'),2)) |
+-----------------------------------------------------------+
| POINT(2 2)                                                |
+-----------------------------------------------------------+

StartPoint(ls)

Returns the Point that is the start point of the LineString value ls.

mysql> SELECT AsText(StartPoint(GeomFromText('LineString(1 1,2 2,3 3)')));
+-------------------------------------------------------------+
| AsText(StartPoint(GeomFromText('LineString(1 1,2 2,3 3)'))) |
+-------------------------------------------------------------+
| POINT(1 1)                                                  |
+-------------------------------------------------------------+

The OpenGIS specification also defines the following function, which MySQL does not yet implement:

IsRing(ls)

Returns 1 if the LineString value ls is closed (thatis, its StartPoint() and EndPoint() 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.

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