2

ST_LineCrossingDirection

 3 years ago
source link: http://postgis.net/docs/ST_LineCrossingDirection.html
Go to the source link to view the article. You can view the picture content, updated content and better typesetting reading experience. If the link is broken, please click the button below to view the snapshot at that time.
neoserver,ios ssh client
ST_LineCrossingDirection

Synopsis

integer ST_LineCrossingDirection(geometry linestringA, geometry linestringB);

Description

Given 2 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

Examples

st_linecrossingdirection01.png

Line 1 (green), Line 2 ball is start point, triangle are end points. Query below. 

SELECT ST_LineCrossingDirection(foo.line1, foo.line2) As l1_cross_l2 ,
	  ST_LineCrossingDirection(foo.line2, foo.line1) As l2_cross_l1
FROM (
SELECT
 ST_GeomFromText('LINESTRING(25 169,89 114,40 70,86 43)') As line1,
 ST_GeomFromText('LINESTRING(171 154,20 140,71 74,161 53)') As line2
	) As foo;

 l1_cross_l2 | l2_cross_l1
-------------+-------------
           3 |          -3
st_linecrossingdirection02.png

Line 1 (green), Line 2 (blue) ball is start point, triangle are end points. Query below.

SELECT ST_LineCrossingDirection(foo.line1, foo.line2) As l1_cross_l2 ,
	  ST_LineCrossingDirection(foo.line2, foo.line1) As l2_cross_l1
FROM (
 SELECT
  ST_GeomFromText('LINESTRING(25 169,89 114,40 70,86 43)') As line1,
  ST_GeomFromText('LINESTRING (171 154, 20 140, 71 74, 2.99 90.16)') As line2
) As foo;

 l1_cross_l2 | l2_cross_l1
-------------+-------------
           2 |          -2
st_linecrossingdirection03.png

Line 1 (green), Line 2 (blue) ball is start point, triangle are end points. Query below. 

SELECT
	ST_LineCrossingDirection(foo.line1, foo.line2) As l1_cross_l2 ,
	ST_LineCrossingDirection(foo.line2, foo.line1) As l2_cross_l1
FROM (
 SELECT
  ST_GeomFromText('LINESTRING(25 169,89 114,40 70,86 43)') As line1,
  ST_GeomFromText('LINESTRING (20 140, 71 74, 161 53)') As line2
  ) As foo;

 l1_cross_l2 | l2_cross_l1
-------------+-------------
          -1 |          1
st_linecrossingdirection04.png

Line 1 (green), Line 2 (blue) ball is start point, triangle are end points. Query below.

SELECT ST_LineCrossingDirection(foo.line1, foo.line2) As l1_cross_l2 ,
	  ST_LineCrossingDirection(foo.line2, foo.line1) As l2_cross_l1
FROM (SELECT
	ST_GeomFromText('LINESTRING(25 169,89 114,40 70,86 43)') As line1,
	ST_GeomFromText('LINESTRING(2.99 90.16,71 74,20 140,171 154)') As line2
	) As foo;

 l1_cross_l2 | l2_cross_l1
-------------+-------------
          -2 |          2
				
SELECT s1.gid, s2.gid, ST_LineCrossingDirection(s1.the_geom, s2.the_geom)
	FROM streets s1 CROSS JOIN streets s2 ON (s1.gid != s2.gid AND s1.the_geom && s2.the_geom )
WHERE ST_CrossingDirection(s1.the_geom, s2.the_geom) > 0;

report

Recommend

About Joyk


Aggregate valuable and interesting links.
Joyk means Joy of geeK