ST_DumpSegments
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## Name

ST_DumpSegments — Returns a set of `geometry_dump` rows for the segments in a geometry.

## Synopsis

`geometry_dump[] ST_DumpSegments(`geometry geom`)`;

## Description

A set-returning function (SRF) that extracts the segments of a geometry. It returns a set of geometry_dump rows, each containing a geometry (`geom` field) and an array of integers (`path` field).

- the `geom` field `LINESTRING`s represent the segments of the supplied geometry.

- the `path` field (an `integer[]`) is an index enumerating the segment start point positions in the elements of the supplied geometry. The indices are 1-based. For example, for a `LINESTRING` the paths are `{i}` where `i` is the `nth` segment start point in the `LINESTRING`. For a `POLYGON` the paths are `{i,j}` where `i` is the ring number (1 is outer; inner rings follow) and `j` is the segment start point position in the ring.

Availability: 3.2.0

This function supports Triangles and Triangulated Irregular Network Surfaces (TIN).

This function supports 3d and will not drop the z-index.

## Standard Geometry Examples

    SELECT path, ST_AsText(geom)
    FROM (
        SELECT (ST_DumpSegments(g.geom)).*
        FROM (SELECT 'GEOMETRYCOLLECTION(
        LINESTRING(1 1, 3 3, 4 4),
        POLYGON((5 5, 6 6, 7 7, 5 5))
    )'::geometry AS geom
            ) AS g
    ) j;

      path   │      st_astext
    ---------------------------------
     {1,1}   │ LINESTRING(1 1,3 3)
     {1,2}   │ LINESTRING(3 3,4 4)
     {2,1,1} │ LINESTRING(5 5,6 6)
     {2,1,2} │ LINESTRING(6 6,7 7)
     {2,1,3} │ LINESTRING(7 7,5 5)
    (5 rows)

## TIN and Triangle Examples

    -- Triangle --
    SELECT path, ST_AsText(geom)
    FROM (
        SELECT (ST_DumpSegments(g.geom)).*
        FROM (SELECT 'TRIANGLE((
            0 0,
            0 9,
            9 0,
            0 0
        ))'::geometry AS geom
            ) AS g
    ) j;

     path  │      st_astext
     ---------------------------------
     {1,1} │ LINESTRING(0 0,0 9)
     {1,2} │ LINESTRING(0 9,9 0)
     {1,3} │ LINESTRING(9 0,0 0)
    (3 rows)

    -- TIN --
    SELECT path, ST_AsEWKT(geom)
    FROM (
        SELECT (ST_DumpSegments(g.geom)).*
        FROM (SELECT 'TIN(((
            0 0 0,
            0 0 1,
            0 1 0,
            0 0 0
        )), ((
            0 0 0,
            0 1 0,
            1 1 0,
            0 0 0
        ))
        )'::geometry AS geom
            ) AS g
    ) j;

      path   │        st_asewkt
      ---------------------------------
     {1,1,1} │ LINESTRING(0 0 0,0 0 1)
     {1,1,2} │ LINESTRING(0 0 1,0 1 0)
     {1,1,3} │ LINESTRING(0 1 0,0 0 0)
     {2,1,1} │ LINESTRING(0 0 0,0 1 0)
     {2,1,2} │ LINESTRING(0 1 0,1 1 0)
     {2,1,3} │ LINESTRING(1 1 0,0 0 0)
    (6 rows)

## See Also

geometry_dump, Section 15.6, “PostGIS Geometry / Geography / Raster Dump Functions”, ST_Dump, ST_DumpRings

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