Description

Computes the line which is the section of the input line starting and ending at the given fractional locations. The first argument must be a LINESTRING. The second and third arguments are values in the range [0, 1] representing the start and end locations. For geometry inputs, the fractions are measured in 2D line length. The Z and M values are interpolated for added endpoints if present.

Si startfraction et endfraction ont la même valeur, cela équivaut à ST_LineInterpolatePoint.

Amélioration : 3.4.0 - La prise en charge de la géographie a été introduite.

Modifié : 2.1.0. Jusqu'à la version 2.0.x, cette fonction était appelée ST_Line_Substring.

Disponibilité : 1.1.0, prise en charge des Z et M ajoutée dans la 1.1.1

Cette fonction prend en charge la 3D et ne supprime pas l'indice z.

Exemples

SELECT ST_AsText(ST_LineSubstring(
    'LINESTRING (20 180, 50 20, 90 80, 120 40, 180 150)',
    0.333,
    0.666));

LINESTRING (45.17311810399485 45.74337011202746, 50 20, 90 80, 112.97593050157862 49.36542599789519)

Si les points de départ et d'arrivée sont identiques, le résultat est un POINT.

SELECT ST_AsText(ST_LineSubstring(
    'LINESTRING(25 50, 100 125, 150 190)',
    0.333,
    0.333));

POINT(69.28469348539744 94.28469348539744)

Une requête pour découper une LineString en sections de longueur 100 ou moins. Elle utilise generate_series() avec un CROSS JOIN LATERAL pour produire l'équivalent d'une boucle FOR.

WITH data(id, geom) AS (VALUES
        ( 'A', 'LINESTRING( 0 0, 200 0)'::geometry ),
        ( 'B', 'LINESTRING( 0 100, 350 100)'::geometry ),
        ( 'C', 'LINESTRING( 0 200, 50 200)'::geometry )
    )
SELECT id, i,
       ST_AsText(ST_LineSubstring(geom, startfrac, LEAST( endfrac, 1 )) ) AS geom
FROM (
    SELECT id, geom, ST_Length(geom) len, 100 sublen FROM data
    ) AS d
CROSS JOIN LATERAL (
    SELECT i, (sublen * i) / len AS startfrac,
              (sublen * (i+1)) / len AS endfrac
    FROM generate_series(0, floor( len / sublen )::integer ) AS t(i)
    -- skip last i if line length is exact multiple of sublen
    WHERE (sublen * i) / len <
> 1.0
    ) AS d2;

id | i |            geom
----+---+-----------------------------
 A  | 0 | LINESTRING(0 0,100 0)
 A  | 1 | LINESTRING(100 0,200 0)
 B  | 0 | LINESTRING(0 100,100 100)
 B  | 1 | LINESTRING(100 100,200 100)
 B  | 2 | LINESTRING(200 100,300 100)
 B  | 3 | LINESTRING(300 100,350 100)
 C  | 0 | LINESTRING(0 200,50 200)

Mesures de mise en œuvre de la geography le long d'un sphéroïde, geometry le long d'une ligne

SELECT ST_AsText(ST_LineSubstring(
    'LINESTRING(-118.2436 34.0522, -71.0570 42.3611)'::geography,
    0.333,
    0.666),
    6) AS geog_sub,
    ST_AsText(ST_LineSubstring(
        'LINESTRING(-118.2436 34.0522, -71.0570 42.3611)'::geometry,
        0.333,
        0.666),
        6) AS geom_sub;

geog_sub                         |                         geom_sub
---------------------------------------------------------+----------------------------------------------------------
 LINESTRING(-103.911641 38.931128,-87.941787 41.831072) | LINESTRING(-102.530462 36.819064,-86.817324 39.585927)

For geometry inputs, the fractional locations are based on the 2D length of the line, even when the input has Z values. The resulting Z values are interpolated along the selected 2D location.

WITH data AS (
          SELECT 'LINESTRING Z (0 0 0, 0 2 5, 0 10 10)'::geometry AS geom
        )
        SELECT ST_Length(geom) AS length_2d,
               ST_3DLength(geom) AS length_3d,
               ST_AsText(ST_LineSubstring(geom, 0, 0.5)) AS substring
        FROM data;

length_2d |    length_3d     |              substring
        -----------+------------------+-------------------------------------
                10 | 14.819145939191106 | LINESTRING Z (0 0 0,0 2 5,0 5 6.875)

Voir aussi

ST_Length, ST_LineExtend, ST_LineInterpolatePoint, ST_LineMerge