[postgis-users] ST_MakeLine() woes

[georgew]

Hi, I have the following code (based on the blog:
http://blog.mathieu-leplatre.info/drape-lines-on-a-dem-with-postgis.html):

WITH line AS
-- From an arbitrary line
(SELECT geom from foot_cl where (sheet='AT24' AND sid=463)),
cells AS
-- Get DEM elevation for each intersected cell
(SELECT ST_Centroid((ST_Intersection(at24.rast, line.geom)).geom) AS geom,
(ST_Intersection(at24.rast, line.geom)).val AS val
FROM at24, line
WHERE ST_Intersects(at24.rast, line.geom)),
-- Instantiate 3D points, ordered on line
points3d AS
(SELECT ST_SetSRID(ST_MakePoint(ST_X(cells.geom), ST_Y(cells.geom), val),
2193) AS geom
FROM cells, line)
select * from points3d

which produces a series of points with the correct shape of the line.
If however I replace the last  line with:

SELECT ST_MakeLine(points3d.geom ORDER BY
ST_Distance(ST_StartPoint(line.geom), cells.geom)) FROM points3d,line,cells

I end up with a line shape which bears only a faint resemblance to what it
should be, i.e. the points are not in the correct sequence.
What is wrong with what I am doing and how can I get the points in the
correct sequence?
Many thanks






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