User's Guide and Reference

Multilinestrings

A multilinestring is a collection of linestrings. Multilinestrings are simple if they intersect only at the endpoints of the linestring elements. Multilinestrings are non-simple if the interiors of the linestring elements intersect.

The boundary of a multilinestring is the non-intersected endpoints of the linestring elements. The multilinestring is closed if all of its linestring elements are closed. The boundary of a multilinestring is NULL if all of the endpoints of all of the elements are intersected. In addition to the other properties inherited from the superclass geometry, multilinestrings have length. Multilinestrings are used to define streams or road networks.

Functions that operate on multilinestrings:

ST_Length

Takes a multilinestring and returns the cumulative length of all its linestring elements as a double precision number. For more information, see ST_Length.

ST_IsClosed

Takes a multilinestring and returns 1 (TRUE) if the multilinestring is closed and 0 (FALSE) otherwise. For more information, see ST_IsClosed.

ST_NumGeometries

Takes a homogeneous collection and returns the number of base geometry elements it contains. For more information, see ST_NumGeometries.

ST_GeometryN

Takes a homogeneous collection and an index and returns the nth base geometry. For more information, see ST_GeometryN.

Figure 12. Multilinestrings.

1. A simple multilinestring whose boundary is defined by the four endpoints of its two linestring elements.
2. A simple multilinestring because only the endpoints of the linestring elements intersect. The boundary is defined by the two non-intersecting endpoints.
3. A non-simple linestring because the interior of one of its linestring elements is intersected. The boundary of this multilinestring is defined by the four endpoints, including the intersecting point.
4. A simple non-closed multilinestring. It is not closed because its element linestrings are not closed. It is simple because none of the interiors of any of the element linestrings are intersected.
5. A simple closed multilinestring. It is closed because all of its elements are closed. It is simple because none of its elements are intersected at the interiors.