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I am trying to find the common intersections between several multi line segments in postgis. I have a solution, it seems to work for small data networks,but it takes its time for large networks. My set up is

create table test(id serial, name text );

ALTER TABLE test ADD PRIMARY KEY (id); select addGeometryColumn('test','the_geom',3857,'MULTILINESTRING',2); create table test_results(id serial, name text ); ALTER TABLE test_results ADD PRIMARY KEY (id); select addGeometryColumn('test_results','the_geom',3857,'MULTILINESTRING',2); Load some data

insert into test (name,the_geom) values('Line_1',st_setsrid(ST_LineMerge( ST_GeomFromText('MULTILINESTRING((1 1,2 2,3 3),(4 4 ,5 5))')),3857)); insert into test (name,the_geom) values('Line_2',st_setsrid(ST_LineMerge( ST_GeomFromText('MULTILINESTRING((1 1,2 2,3 0,0 0,0 4),(4 4 ,5 5))')),3857));insert into test (name,the_geom) values('Line_3',st_setsrid(ST_LineMerge( ST_GeomFromText('MULTILINESTRING((1 1,2 2,4 4,0 0,0 4),(4 4 ,5 5))')),3857));

Compute all matching segments

insert into test_results(name,the_geom) select t1.name|| ' '|| t2.name as name  ,st_intersection(t1.the_geom,t2.the_geom) as  the_geom from test t1, test t2 where st_intersects(t1.the_geom,t2.the_geom) and  st_equals(t1.the_geom ,t2.the_geom)=false;

i.e. find every intersection in every line where the lines are not same as each other. It gives the following results in qgis

where Line 1 green Line 2 red Line 3 yellow Combine Black

Is there a faster way of getting this to work ? enter image description here

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