Hi, i'm a postgis beginner, too, but i think i see the problem, if not
the exact solution:
Point 27 is the /first /point that postgis found that matched your
search-and-snap criteria, not the /best/ (closest) point.
You need to somehow get all the candidate points (ones that match the
criteria), sort (order by) by distance, and use the first one.
Easier said than done maybe, but that's my guess...
Martin Feuchtwanger feu...@shaw.ca 604-254-0361
302 - 1429 E 4th Ave, Vancouver, BC V5N 1J6
http://members.shaw.ca/geomatics.developer
On 21/11/2012 1:50 PM, Guillaume Drolet wrote:
Hi Nicolas,
I didn't quite follow the tips in the "Closing Coutour" thread but got
some inspiration from it (I think it's a bit complicated for my
PostGIS level).
I can now snap lines but some of them (see attached file) don't snap
at the right place. In the attached image, I want the last point of
the line in the southern area (the un-numbered point closest to the
north area in grey) to snap to point 26. Unfortunately, it is point 27
that snapped to 26. The second image shows another case where the snap
didn't do as I expected (multi snaps on the same line..). In some
other cases however, it did work alright.
I'm sure this has to do with the conditions in my query below but I
don't understand what. Maybe you have some clues about it?
DROP TABLE IF EXISTS hydrology.snappedlines;
SELECT b.gid, ST_Snap(a.geom_intersections, b.geom_intersections, 50) geom
INTO TABLE hydrology.snappedlines
FROM hydrology.nhn_coursdeau_merge_test a, -- lines in the north area
hydrology.bdtq_20k_hydro_lo_merge_test b, -- lines in the south area
hydrology.test_north c, -- north area polygon
hydrology.test_south d -- south area polygon
WHERE ST_DWithin(a.geom_intersections, b.geom_intersections, 50) --
units in meters
AND ST_DWithin(a.geom_intersections, c.geom, 0.001)
AND ST_DWithin(a.geom_intersections, d.geom, 0.001)
AND ST_DWithin(b.geom_intersections, c.geom, 0.001)
AND ST_DWithin(b.geom_intersections, d.geom, 0.001);
Thanks for helping,
Guillaume
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