H2GIS

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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