The ST_LineString data type is a one-dimensional object
stored as a sequence of points defining a linear interpolated path.
ST_LineString types are often used to define linear features such
as roads, rivers, and power lines.
Properties
An ST_LineString is simple if
it does not intersect its interior. The endpoints (the boundary) of
a closed ST_LineString occupy the same point in space. An ST_LineString
is a ring if it is both closed and simple. In addition to properties
inherited from the superclass ST_Geometry, ST_LineString values have
length.
The endpoints normally form the boundary of a ST_LineString
unless the ST_LineString is closed, in which case the boundary is
NULL. The interior of a ST_LineString is the connected path that lies
between the endpoints, unless it is closed, in which case the interior
is continuous. The following figure shows examples of ST_LineString
objects: (1) is a simple nonclosed ST_LineString; (2) is a nonsimple
nonclosed ST_LineString; (3) is a closed simple ST_LineString and
therefore is a ring; (4) is a closed nonsimple ST_LineString—it is
not a ring. Figure 1: Examples
of ST_LineString objects
Functions
The following functions operate
on ST_LineString:
ST_StartPoint()
The function returns the linestring's first point.
ST_EndPoint()
The function returns the linestring's last point.
ST_PointN()
The function takes an ST_LineString and an index to nth
point and returns that point.
ST_Length()
The function returns the linestring's length as a double-precision
number.
ST_NumPoints()
The function returns the number of points in the linestring's
sequence as an integer.
ST_IsRing()
The function returns t (TRUE) if the ST_LineString
is a ring and f (FALSE) otherwise.
ST_IsClosed()
The function returns t (TRUE) if the ST_LineString
is closed and f (FALSE) otherwise.
ST_Polygon()
The function creates a polygon from an ST_LineString that is a
ring.
