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I have a PostGIS table testtin2 which is a sort of pseudo TIN consisting of a single multilinestring geometry, which I am intersecting with another table align, also a multilinestring, to generate a set of coordinates along an alignment (or alignments) via the following query...

SELECT ST_X(q1.int_pnt), ST_Y(q1.int_pnt), ST_Z(q1.int_pnt)
FROM
(SELECT ST_Intersection(align.geom, testtin2.geom) as int_pnt 
FROM align INNER JOIN testtin2 ON ST_Intersects(align.geom, testtin2.geom)
WHERE ST_isvalid(align.geom)='t' AND ST_isvalid(testtin2.geom)='t') As q1;

Which works fine except for the fact that the resulting output is seemingly in a 'random' order. Is there a way this query might be modified or re-written such that the coordinates come out in the correct linear sequence along the alignment linestring(s) from the align table?

I need this to happen so that the drafting software I am passing the coordinates to will join the dots up in the correct order.

Thanks in advance.

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...actually I suspect it may help if I break my alignment multilinestring into linestrings either beforehand or in the query somehow but I am not sure how to do this either. – Will Jun 18 '12 at 11:12

closed as too localized by underdark♦ Jul 18 '12 at 13:36

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1 Answer

up vote 0 down vote

Fixed it. Recreated the align table as linestrings (as opposed to a single multilinestring record) and then used the linear referencing function ST_line_locate_point to calculate the distance of each coordinate along the line it belonged to, before ordering the results by this value.

Thanks to anyone who looked.

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