ST_Dump
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Nome

ST_Dump — Returns a set of geometry_dump rows for the components of a geometry.

Sinopse

geometry_dump[] ST_Dump(geometry g1);

Descrição

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

For an atomic geometry type (POINT,LINESTRING,POLYGON) a single record is returned with an empty path array and the input geometry as geom. For a collection or multi-geometry a record is returned for each of the collection components, and the path denotes the position of the component inside the collection.

ST_Dump is useful for expanding geometries. It is the inverse of a ST_Collect / GROUP BY, in that it creates new rows. For example it can be use to expand MULTIPOLYGONS into POLYGONS.

Melhorias: 2.0.0 suporte para superfícies poliédricas, triângulos e TIN introduzido.

Availability: PostGIS 1.0.0RC1. Requires PostgreSQL 7.3 or higher.

[Nota]

Anteriores a 1.3.4, essa função falha se usada com geometrias que contêm CURVAS. Isso é consertado em 1.3.4+

This method supports Circular Strings and Curves.

This function supports Polyhedral surfaces.

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

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

Exemplos

Dump the components of geometries stored in a table.

Code
SELECT sometable.field1,
       (ST_Dump(sometable.geom)).geom AS geom
FROM sometable;

Break a CompoundCurve into its constituent LineStrings and CircularStrings.

Code
SELECT a.geom, ST_HasArc(a.geom)
  FROM ( SELECT (ST_Dump(p_geom)).geom AS geom
         FROM (SELECT 'COMPOUNDCURVE(CIRCULARSTRING(0 0,1 1,1 0),(1 0,0 1))'::geometry AS p_geom) AS b
        ) AS a;
Raster Outputs
st_asewkt          | st_hasarc
-----------------------------+----------
 CIRCULARSTRING(0 0,1 1,1 0) | t
 LINESTRING(1 0,0 1)         | f
(2 rows)
Figure
Geometry figure for visual-st-dump-01

This example breaks a PolyhedralSurface into its faces.

Code
SELECT (a.p_geom).path[1] As path,(a.p_geom).geom As geom_ewkt
  FROM (SELECT ST_Dump('POLYHEDRALSURFACE(
((0 0 0,0 0 1,0 1 1,0 1 0,0 0 0)),
((0 0 0,0 1 0,1 1 0,1 0 0,0 0 0)),((0 0 0,1 0 0,1 0 1,0 0 1,0 0 0)),((1 1 0,1 1 1,1 0 1,1 0 0,1 1 0)),
((0 1 0,0 1 1,1 1 1,1 1 0,0 1 0)),((0 0 1,1 0 1,1 1 1,0 1 1,0 0 1))
)' ) AS p_geom )  AS a;
Raster Outputs
path |                geom_ewkt
------+------------------------------------------
    1 | POLYGON((0 0 0,0 0 1,0 1 1,0 1 0,0 0 0))
    2 | POLYGON((0 0 0,0 1 0,1 1 0,1 0 0,0 0 0))
    3 | POLYGON((0 0 0,1 0 0,1 0 1,0 0 1,0 0 0))
    4 | POLYGON((1 1 0,1 1 1,1 0 1,1 0 0,1 1 0))
    5 | POLYGON((0 1 0,0 1 1,1 1 1,1 1 0,0 1 0))
    6 | POLYGON((0 0 1,1 0 1,1 1 1,0 1 1,0 0 1))
Figure
Geometry figure for visual-st-dump-02

This example uses a TIN geometry.

Code
SELECT (g.gdump).path,(g.gdump).geom as wkt
  FROM
    (SELECT
       ST_Dump('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
            ))
            )' ) AS gdump
    ) AS g;
Raster Outputs
path |                 wkt
------+-------------------------------------
 {1}  | TRIANGLE((0 0 0,0 0 1,0 1 0,0 0 0))
 {2}  | TRIANGLE((0 0 0,0 1 0,1 1 0,0 0 0))
Figure
Geometry figure for visual-st-dump-03