ST_SharedPaths-PolarDB(PolarDB)-阿里云帮助中心

Returns a geometry collection of paths shared by two lineal geometry objects. Use ST_SharedPaths to detect overlapping segments between line geometries, such as shared road segments in a road network.

Syntax

geometry ST_SharedPaths(geometry lineal1, geometry lineal2)

Parameters

Parameter	Description
`lineal1`	The first lineal geometry (LINESTRING or MULTILINESTRING). The direction of this geometry determines how shared paths are classified in the result.
`lineal2`	The second lineal geometry (LINESTRING or MULTILINESTRING).

Return value

A GeometryCollection with two elements:

First element: Paths that run in the same direction as lineal1.
Second element: Paths that run in the opposite direction to lineal1.

Both elements are returned as MULTILINESTRING. If no paths fall into a category, the corresponding element is MULTILINESTRING EMPTY.

Examples

Same-direction shared paths

The two line geometries share the segment (0 0,0 1) and travel in the same direction, so the shared path appears in the first element of the result.

SELECT
  ST_AsText(ST_GeometryN(g, 1)) AS same_direction,
  ST_AsText(ST_GeometryN(g, 2)) AS opposite_direction
FROM (
  SELECT ST_SharedPaths(
    'LINESTRING(-1 0,0 0,0 1)'::geometry,
    'LINESTRING(0 0,0 1,1 1)'::geometry
  ) AS g
) AS t;

Result:

     same_direction      | opposite_direction
-------------------------+-----------------------
 MULTILINESTRING((0 0,0 1)) | MULTILINESTRING EMPTY
(1 row)

Opposite-direction shared paths

Reversing the direction of lineal1 causes the same shared segment to appear in the second element instead.

SELECT
  ST_AsText(ST_GeometryN(g, 1)) AS same_direction,
  ST_AsText(ST_GeometryN(g, 2)) AS opposite_direction
FROM (
  SELECT ST_SharedPaths(
    'LINESTRING(0 1,0 0,-1 0)'::geometry,
    'LINESTRING(0 0,0 1,1 1)'::geometry
  ) AS g
) AS t;

Result:

 same_direction  |    opposite_direction
-----------------+---------------------------
 MULTILINESTRING EMPTY | MULTILINESTRING((0 1,0 0))
(1 row)

What's next

To process the returned GeometryCollection, use these functions:

ST_GeometryN(g, n) — Extract the nth element (1 for same-direction, 2 for opposite-direction paths).