CODEWITHSUNDEEP
postgispostgresql-10multilinestring
Cyrus the Great
Cyrus the Great

Reputation: 5932

STLineMerge do not make my MULTILINESTRING in to LINESTRING

This is my part of multilinestring :

MULTILINESTRING((59.6338836103678 36.3408616511151,59.6336405351758 36.3410074124113),(59.648377513513 36.3329201331362,59.6481338515878 36.3326094998047,59.6478482801467 36.3322287937626))

When i execute this command in postgresql :

SELECT  ST_AsText(ST_LineMerge(ST_GeomFromText('MULTILINESTRING((59.6338836103678 36.3408616511151,59.6336405351758 36.3410074124113),(59.648377513513 36.3329201331362,59.6481338515878 36.3326094998047,59.6478482801467 36.3322287937626))')));

I do not get linestring?I got still MULTILINESTRING ?

Upvotes: 2

Views: 2386

Answers (2)

Grzegorz Grabek
Grzegorz Grabek

Reputation: 980

I assume that you want to merge multilinestring to one linestring if possible if not then merge to N linestrings where N is the lowest possible number of linestrings.

I add another multilinestring that can be marged to one linestring to check if it works as intented.

with  edges as (select ST_GeomFromText('MULTILINESTRING((59.6338836103678 36.3408616511151,59.6336405351758 36.3410074124113),
                                                        (59.648377513513 36.3329201331362,59.6481338515878 36.3326094998047,59.6478482801467 36.3322287937626))') geom
                UNION
                select ST_GeomFromText('MULTILINESTRING((0 0,1 1),
                                                        (1 1,30 20,100 120)
                                                       )') geom)

select row_number() over () id,geom, st_astext(geom)
    FROM (select distinct (st_dump(st_linemerge(geom))).geom geom
            from (select st_union(geom) geom
                    from edges e) a
         ) b;

Upvotes: 2

mlinth
mlinth

Reputation: 3118

It's returning the original multilinestring, which st_linemerge does when it can't merge. It looks like your multilinestring has separate pieces which is why it cannot be merged. I get the following when I put it into QGIS.

enter image description here

There is some more information on this issue here: https://gis.stackexchange.com/questions/83069/cannot-st-linemerge-a-multilinestring-because-its-not-properly-ordered

Upvotes: 3

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