ST_LongestLine

Signature

LINESTRING ST_LongestLine(GEOMETRY geomA, GEOMETRY geomB);

Description

Returns the 2-dimensional longest LINESTRING between the points of two geometries (geomA and geomB).

If geomA and geomB are the same, the function will return the longest LINESTRING between the two farthest vertices in this geometry.

Examples

Cases where `geomA` and `geomB` are different

SELECT ST_Longestline('POLYGON ((0 1, 1 1, 1 0, 0 0, 0 1))', 
                      'POLYGON ((2 3, 2 2, 3 2, 4 3, 2 3))');
-- Answer: LINESTRING (0 0, 4 3)

SELECT ST_Longestline('POLYGON ((0 1, 1 1, 1 0, 0 0, 0 1))', 
		      'LINESTRING (1 3, 4 3)');
-- Answer: LINESTRING (0 0, 4 3)

SELECT ST_Longestline('POLYGON ((0 1, 1 1, 1 0, 0 0, 0 1))', 
		      'POINT (3 2)');
-- Answer: LINESTRING (0 0, 3 2)

SELECT ST_Longestline('MULTIPOLYGON (((0 1, 1 1, 1 0, 0 0, 0 1)), 
				    ((2 3, 2 2, 3 3, 2 3)))', 
		      'POINT (3 2)');
-- Answer: LINESTRING (0 0, 3 2)

Case where `geomA` is equal to `geomB`

SELECT ST_Longestline('POLYGON ((1 3, 0 0, 3 2, 1 3))', 
		      'POLYGON ((1 3, 0 0, 3 2, 1 3))');
-- Answer: LINESTRING (0 0, 3 2)

See also