[postgis-users] breake lines

[Martin Davis]

On Thu, Sep 5, 2019 at 6:38 AM <paul.malm at lfv.se> wrote:

>
>
>
> Result*: all of the lines* from LayerToBeSplitted where copied into tmp2*,
> not just the ones NOT intersecting*, and I don't know how to
>
> get the attributes to be transferred to tmp2 for those new lines.
>

To get the lines from LayerToBeSplitted which don't intersect ANY lines
from LayerToSplitWith, you need to use this SQL pattern:

SELECT d.* FROM LayerToBeSplitted d
LEFT JOIN LayerToSplitWith c ON ST_Intersects(d.geom, c.geom)
WHERE c.geom IS NULL

(Your query is including lines if there is SOME cutting line which isn't
intersected, which will generally always be the case)

Here's an updated example query which does both split and non-split
together:

WITH
data AS (
    SELECT * FROM (VALUES
        ( 1, 'LINESTRING (100 100, 400 100)'::geometry ),
        ( 2, 'LINESTRING (100 300, 400 300)'::geometry ),
        ( 3, 'LINESTRING (250 400, 400 400)'::geometry ),
        ( 4, 'LINESTRING (-10 -10, -20 -20)'::geometry ),
        ( 5, 'LINESTRING (-30 -30, -40 -40)'::geometry )
    ) AS t(id, geom)
),
cutter AS (
    SELECT * FROM (VALUES
        ( 'LINESTRING (150 50, 150 350)'::geometry ),
        ( 'LINESTRING (200 50, 200 150)'::geometry ),
        ( 'LINESTRING (250 350, 250 250)'::geometry ),
        ( 'LINESTRING (300 350, 300 50)'::geometry ),
        ( 'LINESTRING (350 250, 350 450)'::geometry )
    ) AS t(geom)
)
SELECT * FROM (SELECT id, ST_Split( d.geom,
            (SELECT ST_Collect(c.geom) geom
                FROM cutter c WHERE ST_Intersects(d.geom, c.geom)
            )) geom
    FROM data d) AS t WHERE geom IS NOT NULL
UNION
SELECT d.id, d.geom
    FROM data d
    LEFT JOIN cutter c ON ST_Intersects(d.geom, c.geom)
    WHERE c.geom IS NULL;
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