Hi, Not having tried this, but perhaps:
Use ST_Polygonize() on the linestrings as in the example here: http://postgis.org/docs/ST_Polygonize.html You could use ST_Dump() to return the polygons & wrap it up in count() for the where clause, so only linestrings able to generate one or more polygons are returned. This should identify the self-crossing linestrings, as only such linestrings can form a closed polygon boundary. HTH, Brent Wood --- On Sun, 2/19/12, Hilton Long <seldoms...@scinternet.net> wrote: From: Hilton Long <seldoms...@scinternet.net> Subject: [postgis-users] Need help detecting lassos To: postgis-users@postgis.refractions.net Date: Sunday, February 19, 2012, 11:58 AM I’d like to be able to detect all line loops that are not closed, but where one end of the line loops around and terminates on another line (a lasso). Querying a table containing several of these returns no ST_IsClosed=true, or ST_IsValid=false, or ST_IsSimple=false. Ultimately, I’d like to split the original loop into a line segment = two loop halves. Thanks In Advance. -----Inline Attachment Follows----- _______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
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