ST_LineCrossingDirection — Returns a number indicating the crossing behavior of two LineStrings
integer ST_LineCrossingDirection(geometry linestringA, geometry linestringB);
Given two linestrings returns an integer between -3 and 3
indicating what kind of crossing behavior exists between them.
0 indicates no crossing.
This is only supported for LINESTRINGs.
The crossing number has the following meaning:
0: LINE NO CROSS
-1: LINE CROSS LEFT
1: LINE CROSS RIGHT
-2: LINE MULTICROSS END LEFT
2: LINE MULTICROSS END RIGHT
-3: LINE MULTICROSS END SAME FIRST LEFT
3: LINE MULTICROSS END SAME FIRST RIGHT
Availability: 1.4
Example: LINE CROSS LEFT and LINE CROSS RIGHT
SELECT ST_LineCrossingDirection(lineA, lineB) As A_cross_B,
ST_LineCrossingDirection(lineB, lineA) As B_cross_A
FROM (SELECT
'LINESTRING(25 169,89 114,40 70,86 43)'::geometry As lineA,
'LINESTRING (20 140,71 74,161 53)'::geometry As lineB
) As foo;
A_cross_B | B_cross_A
-----------+-----------
-1 | 1
Example: LINE MULTICROSS END SAME FIRST LEFT and LINE MULTICROSS END SAME FIRST RIGHT
SELECT ST_LineCrossingDirection(lineA, lineB) As A_cross_B,
ST_LineCrossingDirection(lineB, lineA) As B_cross_A
FROM (SELECT
'LINESTRING(25 169,89 114,40 70,86 43)'::geometry As lineA,
'LINESTRING(171 154,20 140,71 74,161 53)'::geometry As lineB
) As foo;
A_cross_B | B_cross_A
-----------+-----------
3 | -3
Example: LINE MULTICROSS END LEFT and LINE MULTICROSS END RIGHT
SELECT ST_LineCrossingDirection(lineA, lineB) As A_cross_B,
ST_LineCrossingDirection(lineB, lineA) As B_cross_A
FROM (SELECT
'LINESTRING(25 169,89 114,40 70,86 43)'::geometry As lineA,
'LINESTRING(5 90,71 74,20 140,171 154)'::geometry As lineB
) As foo;
A_cross_B | B_cross_A
-----------+-----------
-2 | 2
Example: Finds all streets that cross
SELECT s1.gid, s2.gid, ST_LineCrossingDirection(s1.geom, s2.geom)
FROM streets s1 CROSS JOIN streets s2
ON (s1.gid != s2.gid AND s1.geom && s2.geom )
WHERE ST_LineCrossingDirection(s1.geom, s2.geom) > 0;