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

[Andreas Neumann]

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

-- 
Andreas Neumann
Böschacherstrasse 6, CH-8624 Grüt/Gossau, Switzerland
Email: a.neumann at carto.net, Web:
* http://www.carto.net/ (Carto and SVG resources)
* http://www.carto.net/neumann/ (personal page)
* http://www.svgopen.org/ (SVG Open Conference)
* http://www.geofoto.ch/ (Georeferenced Photos of Switzerland)