Covers predicate fails for Line/Point due to geometric robustness

[cuteDen-ECNU]

Geometry Description

The distance from Point c ('POINT( 0.2 0.9)') to Line a ('LINESTRING(2 0, 0 1)') is 0. Line b ('LINESTRING(2 0, 0.2 0.9, 0 1)') is Line a plus Point c.

SELECT ST_Equals(Foo.a, Foo.b), ST_Distance(Foo.a, Foo.c)
    FROM (SELECT ST_GeomFromText('LINESTRING(2 0, 0 1)') As a,
    ST_GeomFromText('LINESTRING(2 0, 0.2 0.9, 0 1)') As b,
    ST_GeomFromText('POINT( 0.2 0.9)') As c) As Foo;

Expected Behavior

Line a should equal Line b. As the example in the document [link](https://postgis.net/docs/ST_Equals.html):

SELECT ST_Equals(g1, g2) As g1Equalsg2
FROM (SELECT ST_GeomFromText('LINESTRING(0 0, 10 10)') As g1,
    ST_GeomFromText('LINESTRING(0 0, 5 5, 10 10)') As g2) As Foo;
 
g1equalsg2 
------------
 t
(1 row)

Actual Behavior

PostGIS doesn’t think Line a equals Line b. The following statement is the same as the statement in the geometry description. The result of st_equals is false which means Postgis doesn’t think they are the same line.

SELECT ST_Equals(Foo.a, Foo.b), ST_Distance(Foo.a, Foo.c)
    FROM (SELECT ST_GeomFromText('LINESTRING(2 0, 0 1)') As a,
    ST_GeomFromText('LINESTRING(2 0, 0.2 0.9, 0 1)') As b,
    ST_GeomFromText('POINT( 0.2 0.9)') As c) As Foo;

st_equals | st_distance
-----------+-------------
f         |           0
(1 row)

Additional Information

SQLServer thinks the two LINESTRINGs are equal.

DECLARE @g1 geometry;DECLARE @g2 geometry;DECLARE @g3 geometry;
SET @g1 = geometry::STGeomFromText ('LINESTRING(2 0, 0 1)',0);
SET @g2 = geometry::STGeomFromText ('LINESTRING(2 0, 0.2 0.9, 0 1)',0);
SET @g3 = geometry::STGeomFromText ('POINT(0.2 0.9)',0);
SELECT @g1.STEquals(@g2) As g1Equalsg2

g1Equalsg2
----------
         1

(1 rows affected)

[cuteDen-ECNU]

bugtracker link: libgeos/geos#968