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ST_Drape

Signature

GEOMETRY ST_Drape(GEOMETRY geomA, GEOMETRY geomB);

Description

This function drapes an input geometry (geomA) to a set of triangles (geomB).

Notes :

  • The supported input geometry types are POINT, MULTIPOINT, LINESTRING, MULTILINESTRING, POLYGON and MULTIPOLYGON
  • In case of 1 or 2 dimension, the input geometry (geomA) is intersected with the triangles to perform a full draping.
  • If a POINT lies on two triangles, the z value of the first triangle is kept.

Examples

Case between a LINESTRING and a POLYGON

SELECT ST_Drape('LINESTRING(1 2, 5 2)',
                'POLYGON((1 1 0, 4 1 0, 4 4 5, 1 1 0))');
-- Answer: LINESTRING(1 2, 2 2 2, 4 2 2, 5 2)

Case between a LINESTRING and a MULTIPOLYGON

SELECT ST_Drape('LINESTRING(1 2, 5 2)',
                'MULTIPOLYGON(((1 1 0, 4 1 0, 4 4 5, 1 1 0))
                              ((4 1 0, 4 4 5, 5 4 5, 4 1 0))');
-- Answer: LINESTRING(1 2, 2 2 1.66, 4 2 1.66, 4.33 2 1.66, 5 2)

Case between two POLYGONS

SELECT ST_Drape('POLYGON((1 2, 5 2, 2 5, 1 2))',
                'POLYGON((1 1 0, 4 1 0, 4 4 5, 1 1 0))');
-- Answer: POLYGON((1 2, 2 2 1.66, 4 2 1.66, 5 2, 
--                  4 3 3.33, 3.5 3.5 4.16, 2 5, 1 2))

Case between two POLYGONS (input one with hole)

SELECT ST_Drape('POLYGON ((1 2, 5 2, 2 5, 1 2),(2 2.5, 2 3.5, 3.5 2.5, 2 2.5))',
                'POLYGON((1 1 0, 4 1 0, 4 4 5, 1 1 0))');
-- Answer: POLYGON((1 2, 2 2 1.66, 4 2 1.66, 5 2, 4 3 3.33, 3.5 3.5 4.16, 2 5, 1 2), 
--                 (2 2.5, 2 3.5, 2.9 2.9 3.16, 3.5 2.5 2.5, 2.5 2.5 2.5, 2 2.5))

Case between a MULTIPOINT and a POLYGON

SELECT ST_Drape('MULTIPOINT((1 2), (2 2), (3 2), (4 3))',
                'POLYGON((1 1 0, 4 1 0, 4 4 5, 1 1 0))');
-- Answer: MULTIPOINT((1 2), (2 2 1.66), (3 2 1.66), (4 3 3.33))

Case between a MULTILINESTRING and a POLYGON

SELECT ST_Drape('MULTILINESTRING((1 2, 3 2),(2 4, 5 2))',
                'POLYGON((1 1 0, 4 1 0, 4 4 5, 1 1 0))');
-- Answer: MULTILINESTRING((1 2, 2 2 1.66, 3 2 1.66),
--                         (2 4, 3.2 3.2 3.66, 4 2.66 2.77, 5 2))

Case between a MULTIPOLYGON and a POLYGON

SELECT ST_Drape('MULTIPOLYGON(((1 2, 3 2, 2 3, 1 2)),
                              ((2 4, 5 2, 5 5, 2 4)))',
                'POLYGON((1 1 0, 4 1 0, 4 4 5, 1 1 0))');
-- Answer: MULTIPOLYGON(((1 2, 2 2 1.66, 3 2 1.66, 2.5 2.5 2.5, 2 3, 1 2)), 
--                      ((2 4, 3.2 3.2 3.66, 4 2.66 2.77, 5 2, 5 5, 2 4)))

See also