[postgis-users] st_union and simple line merge

[Nicklas Avén]

ok, I found:ST_LineMerge() I just expected that funtionality to be built in st_union but it will solve my problem :-) /Nicklas

2009-12-04 Nicklas Avén wrote:

>
Hallo>
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I found that st_union makes no effort to avoid multilinestring from st_union(linestring, linestring)>
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Is this expected?>
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an example:>
select st_astext(st_union('LINESTRING(1 1, 5 5)'::geometry, 'LINESTRING(5 5, 10 5)'::geometry));>
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returns MULTILINESTRING((1 1,5 5),(5 5,10 5))>
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and worst for practical cases if we input the linestrings in opposite order>
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select st_astext(st_union( 'LINESTRING(5 5, 10 5)'::geometry, 'LINESTRING(1 1, 5 5)'::geometry));>
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we get:>
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"MULTILINESTRING((5 5,10 5),(1 1,5 5))"
>>
This is not described in the documentation but it says that st_union will try to dissolv boudaries, and I can't imagine any simplier case to dissolv boundaries than this. >
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Is this the expected bahavior, is there any other way to merge simple linestrings to new linestrings?>
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Thanks>
Nicklas>
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 >
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