[postgis-users] Merging 2 Linestring to get another Linestring

[Kevin Neufeld]

ST_Collect() the geometries together and then use ST_LineMerge() to 
merge the multilinestring.

This yields a single LineString:
SELECT AsText(ST_LineMerge(ST_Collect('LINESTRING(...)'::geometry, 
'LINESTRING(...)'::geometry)));

Cheers,
Kevin

Andreas Neumann wrote:
> Hi,
>
> I am trying to merge two adjacent LINESTRING, which share one coordinate.
> I tried several methods including ST_LineMerge(), ST_Union(), ST_COLLECT()
> but I always get a MULTILINESTRING (with 2 lines) and not one LINESTRING.
> I am sure that the two LINESTRINGS share one coordinate.
>
> Here are the two LINESTRINGS:
> LINESTRING(698743.275 247423.051,698736.415 247418.128,698729.24798758
> 247421.79729034,698730.68588476 247411.21739393,698727.44597887
> 247408.23890492,698720.60897496 247402.31714286,698695.08735303
> 247377.58230291,698688.7535124 247371.68476191,698687.7687112
> 247370.76779766,698668.50284867 247359.12136294,698659.14969397
> 247355.5832141,698607.8062372 247337.32603572,698578.70982688
> 247326.19051288,698551.37595726 247318.7513057,698498.88241182
> 247309.41108415,698494.06629765 247308.55414883,698466.35518599
> 247300.51456377,698450.40507561 247293.85890908,698437.00424285
> 247295.30551693,698426.725 247318.873,698421.483 247316.59,698407.529
> 247348.734,698393.578 247380.872,698379.644 247412.853,698365.703
> 247444.85,698352.073 247476.204,698319.393 247460.056,698317.925
> 247459.33,698293.723 247447.371,698287.356 247444.225,698268.42
> 247434.205,698262.313 247429.797,698252.121 247424.758,698285.096
> 247378.915,698313.574 247339.323,698312.43749951 247339.0551761,698297.835
> 247335.614,698284.946 247330.848,698263.273 247320.271,698243.567
> 247310.119,698222.168 247310.99,698216.05389007 247311.81569585,698200.74
> 247296.77,698146.526 247244.695,698144.14486829 247242.40781526,698155.343
> 247231.164,698152.892 247228.722,698152.70068758
> 247228.53139008,698163.3329707 247213.81319548,698175.00856403
> 247197.61458341,698233.2746542 247159.85760142,698231.671
> 247157.9,698219.524 247143.072,698180.269 247094.706,698133.958
> 247133.077,698095.594 247176.128,698038.242 247091.136,698036.84324328
> 247089.0631319,698017.72201345 247107.76725733,697983.59952742
> 247136.38272159,697937.81014344 247161.4233732,697904.60984576
> 247169.32667165)
>
> and
>
> LINESTRING(697904.60984576 247169.32667165,697893.1506172
> 247173.90833164,697868.885915 247193.74698711,697863.33904042
> 247202.1075178,697857.41357564 247211.64600192,697840.22672596
> 247230.52556801,697800.40623846 247265.71379369,697795.643
> 247285.35,697787.741 247263.451)
>
> and here is one of the commands I tried:
> SELECT ST_AsText(ST_LineMerge(geom)) FROM (SELECT
> ST_Union(ST_Reverse(the_geom)) AS geom FROM admin.plz WHERE gid > 14) AS
> the_geom;
>
> There are only 16 lines in the db and the gids 15 and 16 are the two I
> want to merge.
>
> Thanks for any hints how I can get a sewed together LINESTRING.
>
> Andreas
>
>