I have a problem to check if a Linestring contains a Point. I consider the straight line y = 0.1 x , and take by it a segment l='Linestring( 0 0 , 4 0.4 )' and a Point p on segment l, p = 'Point(1.5 0.15)'. If I check ST_Contains(l,p) the result is false and the distance ST_Distance(l,p) is near to zero, but this is wrong because the Point is on the Linestring. If I try with p= 'Point(2 0.2)' the result is right.
What is the problem?
Thanks so much.
WITH
l AS (
SELECT ST_GeomFromText('Linestring( 0 0 , 4 0.4 )') AS geom -- segment of the straight line y = 0.1 x
),
p AS (
SELECT ST_GeomFromText('Point(1.5 0.15)') AS geom -- point on the straight line y = 0.1 x
)
SELECT ST_AsText(ST_Intersection(p.geom,l.geom)) as ST_Intersection,
ST_Distance(p.geom,l.geom),
ST_Contains(l.geom,p.geom),
ST_Intersects(p.geom,l.geom),
ST_AsText(ST_Line_Interpolate_Point(l.geom,1.5/4)) as ST_Substring -- point in position 1.5/4 of l
FROM l,p
EDIT: My origin problem was: LineString L1 contains Linestring L2 but if I do ST_SymDifference(l1.geom,l2.geom) the result is incorrect.
WITH
l1 AS (
SELECT ST_GeomFromText('Linestring( 0 0 , 4 0.4 )') AS geom -- segment of the straight line y = 0.1 x
),
l2 AS (
SELECT ST_GeomFromText('LineString(0 0 , 1.5 0.15)') AS geom -- segment of the straight line y = 0.1 x
)
SELECT ST_AsText(ST_SymDifference(l1.geom,l2.geom)) as ST_Intersection
FROM l1,l2
