[postgis-users] [Question] Point returned in ST_LineLocatePoint and ST_ClosestPoint is not able to detect in ST_Contains

[Dharshan Bharathur]

Hi all, Need experts advice.

This is the same question I have asked here.
<http://gis.stackexchange.com/questions/164683/point-returned-from-st-linelocatepoint-returns-false-in-st-contains>

I am using postgis's ST_LineLocatePoint to find out the closest point on a
LineString to the given Point, and using  ST_LineInterpolatePoint to
extract a Point from the returned float number.(as referred here
<http://postgis.net/docs/ST_LineLocatePoint.html>)

This is my ST_LineLocatePoint Query

SELECT ST_AsText(ST_LineInterpolatePoint(foo.the_line,
         ST_LineLocatePoint(foo.the_line,ST_GeomFromText('POINT(12.962315
         77.584841)')))) AS g FROM (SELECT ST_GeomFromText('LINESTRING(12.96145
         77.58408,12.96219 77.58447,12.96302 77.58489,12.96316
77.58496,12.96348
         77.58511)') AS the_line) AS foo;


Output:

                  g
------------------------------------------
 POINT(12.9624389808159 77.5845959902924)

Which exactly lies on the linestring I have passed. Demonstration is
displayed here <http://jsfiddle.net/2p3zekae/2/>.


query with St_Closest function also returns the same points.

But when I check whether this point lies in the same linestring using
ST_Contains it always return false, even though the point lies within.

My ST_Contains Query:
SELECT ST_Contains(ST_GeomFromText('LINESTRING(12.96145 77.58408,12.96219
77.58447,12.96302 77.58489, 12.96316 77.58496, 12.96348 77.58511)'),
ST_GeomFromText('POINT(12.9624389808159 77.5845959902924)'));

Output:
st_contains
-------------
f

I am not getting where I am doing wrong, why I am getting false. Can anyone
help me in this.

I am using Postgresql : 9.4, postgis : 2.1






*Thanks & RegardsDharshan*
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