名稱
ST_LineCrossingDirection — 返回一個數字，指示兩個 LineString 的交叉行為
概要
integer ST_LineCrossingDirection(geometry linestringA, geometry linestringB);
描述
給定兩個線串，返回一個介於 -3 和 3 之間的整數，指示它們之間存在的交叉行為類型。0 表示沒有交叉。此函數僅支援 LINESTRING。
交叉數字的含義如下
-
0：線無交叉
-
-1：線交叉向左
-
1：線交叉向右
-
-2：線多重交叉末端向左
-
2：線多重交叉末端向右
-
-3：線多重交叉末端同首點向左
-
3：線多重交叉末端同首點向右
可用性：1.4
範例
範例：線交叉向左和線交叉向右
藍色：線 A；綠色：線 B
SELECT ST_LineCrossingDirection(lineA, lineB) As A_cross_B,
ST_LineCrossingDirection(lineB, lineA) As B_cross_A
FROM (SELECT
ST_GeomFromText('LINESTRING(25 169,89 114,40 70,86 43)') As lineA,
ST_GeomFromText('LINESTRING (20 140, 71 74, 161 53)') As lineB
) As foo;
A_cross_B | B_cross_A
-----------+-----------
-1 | 1
範例：線多重交叉末端同首點向左和線多重交叉末端同首點向右
藍色：線 A；綠色：線 B
SELECT ST_LineCrossingDirection(lineA, lineB) As A_cross_B,
ST_LineCrossingDirection(lineB, lineA) As B_cross_A
FROM (SELECT
ST_GeomFromText('LINESTRING(25 169,89 114,40 70,86 43)') As lineA,
ST_GeomFromText('LINESTRING(171 154,20 140,71 74,161 53)') As lineB
) As foo;
A_cross_B | B_cross_A
-----------+-----------
3 | -3
範例：線多重交叉末端向左和線多重交叉末端向右
藍色：線 A；綠色：線 B
SELECT ST_LineCrossingDirection(lineA, lineB) As A_cross_B,
ST_LineCrossingDirection(lineB, lineA) As B_cross_A
FROM (SELECT
ST_GeomFromText('LINESTRING(25 169,89 114,40 70,86 43)') As lineA,
ST_GeomFromText('LINESTRING(5 90, 71 74, 20 140, 171 154)') As lineB
) As foo;
A_cross_B | B_cross_A
-----------+-----------
-2 | 2
範例： 尋找所有交叉的街道
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;