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SFCGAL Processing and Relationship Functions

CG_Intersection

Computes the intersection of two geometries

Synopsis

geometry CG_Intersection(geometry
                            geomA, geometry
                            geomB)

Description

Computes the intersection of two geometries.

Performed by the SFCGAL module

Note

NOTE: this function returns a geometry representing the intersection.

Availability: 3.5.0

Geometry Examples

SELECT ST_AsText(CG_Intersection('LINESTRING(0 0, 5 5)', 'LINESTRING(5 0, 0 5)'));
                cg_intersection
                -----------------
                POINT(2.5 2.5)
                (1 row)

CG_Intersects

Tests if two geometries intersect (they have at least one point in common)

Synopsis

boolean CG_Intersects(geometry
                        geomA, geometry
                        geomB)

Description

Returns true if two geometries intersect. Geometries intersect if they have any point in common.

Performed by the SFCGAL module

Note

NOTE: this is the "allowable" version that returns a boolean, not an integer.

Availability: 3.5.0

Geometry Examples

SELECT CG_Intersects('POINT(0 0)'::geometry, 'LINESTRING ( 2 0, 0 2 )'::geometry);
    cg_intersects
    ---------------
    f
    (1 row)
    SELECT CG_Intersects('POINT(0 0)'::geometry, 'LINESTRING ( 0 0, 0 2 )'::geometry);
    cg_intersects
    ---------------
    t
    (1 row)

CG_3DIntersects

Tests if two 3D geometries intersect

Synopsis

boolean CG_3DIntersects(geometry
                    geomA, geometry
                    geomB)

Description

Tests if two 3D geometries intersect. 3D geometries intersect if they have any point in common in the three-dimensional space.

Performed by the SFCGAL module

Note

NOTE: this is the "allowable" version that returns a boolean, not an integer.

Availability: 3.5.0

Geometry Examples

SELECT CG_3DIntersects('POINT(1.2 0.1 0)','POLYHEDRALSURFACE(((0 0 0,0.5 0.5 0,1 0 0,1 1 0,0 1 0,0 0 0)),((1 0 0,2 0 0,2 1 0,1 1 0,1 0 0),(1.2 0.2 0,1.2 0.8 0,1.8 0.8 0,1.8 0.2 0,1.2 0.2 0)))');
        cg_3dintersects
        ---------------
        t
        (1 row)

CG_Difference

Computes the geometric difference between two geometries

Synopsis

geometry CG_Difference(geometry
                    geomA, geometry
                    geomB)

Description

Computes the geometric difference between two geometries. The resulting geometry is a set of points that are present in geomA but not in geomB.

Performed by the SFCGAL module

Note

NOTE: this function returns a geometry.

Availability: 3.5.0

Geometry Examples

SELECT ST_AsText(CG_Difference('POLYGON((0 0, 0 1, 1 1, 1 0, 0 0))'::geometry, 'LINESTRING(0 0, 2 2)'::geometry));
    cg_difference
    ---------------
    POLYGON((0 0,1 0,1 1,0 1,0 0))
    (1 row)

ST_3DDifference

Perform 3D difference

Synopsis

geometry ST_3DDifference(geometry geom1, geometry geom2)

Description

Warning

ST_3DDifference is deprecated as of 3.5.0. Use CG_3DDifference instead.

Returns that part of geom1 that is not part of geom2.

Availability: 2.2.0

SQL-MM IEC 13249-3: 5.1

CG_3DDifference

Perform 3D difference

Synopsis

geometry CG_3DDifference(geometry geom1, geometry geom2)

Description

Returns that part of geom1 that is not part of geom2.

Availability: 3.5.0

SQL-MM IEC 13249-3: 5.1

Examples

3D images were generated using PostGIS ST_AsX3D and rendering in HTML using X3Dom HTML Javascript rendering library.

SELECT CG_Extrude(ST_Buffer(ST_GeomFromText('POINT(100 90)'),
                                50, 'quad_segs=2'),0,0,30) AS geom1,
                                CG_Extrude(ST_Buffer(ST_GeomFromText('POINT(80 80)'),
                                50, 'quad_segs=1'),0,0,30) AS geom2;

Original 3D geometries overlaid. geom2 is the part that will be removed.

SELECT CG_3DDifference(geom1,geom2)
                            FROM ( SELECT CG_Extrude(ST_Buffer(ST_GeomFromText('POINT(100 90)'),
                            50, 'quad_segs=2'),0,0,30) AS geom1,
                            CG_Extrude(ST_Buffer(ST_GeomFromText('POINT(80 80)'),
                            50, 'quad_segs=1'),0,0,30) AS geom2 ) As t;

What's left after removing geom2

CG_Distance

Computes the minimum distance between two geometries

Synopsis

double precision CG_Distance(geometry
                    geomA, geometry
                    geomB)

Description

Computes the minimum distance between two geometries.

Performed by the SFCGAL module

Note

NOTE: this function returns a double precision value representing the distance.

Availability: 3.5.0

Geometry Examples

SELECT CG_Distance('LINESTRING(0.0 0.0,-1.0 -1.0)', 'LINESTRING(3.0 4.0,4.0 5.0)');
        cg_distance
        -------------
        2.0
        (1 row)

CG_3DDistance

Computes the minimum 3D distance between two geometries

Synopsis

double precision CG_3DDistance(geometry
                    geomA, geometry
                    geomB)

Description

Computes the minimum 3D distance between two geometries.

Performed by the SFCGAL module

Note

NOTE: this function returns a double precision value representing the 3D distance.

Availability: 3.5.0

Geometry Examples

SELECT CG_3DDistance('LINESTRING(-1.0 0.0 2.0,1.0 0.0 3.0)', 'TRIANGLE((-4.0 0.0 1.0,4.0 0.0 1.0,0.0 4.0 1.0,-4.0 0.0 1.0))');
        cg_3ddistance
        ----------------
        1
        (1 row)

ST_3DConvexHull

Computes the 3D convex hull of a geometry.

Synopsis

geometry ST_3DConvexHull(geometry geom1)

Description

Warning

ST_3DConvexHull is deprecated as of 3.5.0. Use CG_3DConvexHull instead.

Availability: 3.3.0

CG_3DConvexHull

Computes the 3D convex hull of a geometry.

Synopsis

geometry CG_3DConvexHull(geometry geom1)

Description

Availability: 3.5.0

Examples

SELECT ST_AsText(CG_3DConvexHull('LINESTRING Z(0 0 5, 1 5 3, 5 7 6, 9 5 3 , 5 7 5, 6 3 5)'::geometry));

POLYHEDRALSURFACE Z (((1 5 3,9 5 3,0 0 5,1 5 3)),((1 5 3,0 0 5,5 7 6,1 5 3)),((5 7 6,5 7 5,1 5 3,5 7 6)),((0 0 5,6 3 5,5 7 6,0 0 5)),((6 3 5,9 5 3,5 7 6,6 3 5)),((0 0 5,9 5 3,6 3 5,0 0 5)),((9 5 3,5 7 5,5 7 6,9 5 3)),((1 5 3,5 7 5,9 5 3,1 5 3)))

WITH f AS (SELECT i, CG_Extrude(geom, 0,0, i ) AS geom
        FROM ST_Subdivide(ST_Letters('CH'),5) WITH ORDINALITY AS sd(geom,i)
        )
        SELECT CG_3DConvexHull(ST_Collect(f.geom) )
        FROM f;

Original geometry overlaid with 3D convex hull

ST_3DIntersection

Perform 3D intersection

Synopsis

geometry ST_3DIntersection(geometry geom1, geometry geom2)

Description

Warning

ST_3DIntersection is deprecated as of 3.5.0. Use CG_3DIntersection instead.

Return a geometry that is the shared portion between geom1 and geom2.

Availability: 2.1.0

SQL-MM IEC 13249-3: 5.1

CG_3DIntersection

Perform 3D intersection

Synopsis

geometry CG_3DIntersection(geometry geom1, geometry geom2)

Description

Return a geometry that is the shared portion between geom1 and geom2.

Availability: 3.5.0

SQL-MM IEC 13249-3: 5.1

Examples

3D images were generated using PostGIS ST_AsX3D and rendering in HTML using X3Dom HTML Javascript rendering library.

SELECT CG_Extrude(ST_Buffer(ST_GeomFromText('POINT(100 90)'),
                                    50, 'quad_segs=2'),0,0,30) AS geom1,
                                    CG_Extrude(ST_Buffer(ST_GeomFromText('POINT(80 80)'),
                                    50, 'quad_segs=1'),0,0,30) AS geom2;

Original 3D geometries overlaid. geom2 is shown semi-transparent

SELECT CG_3DIntersection(geom1,geom2)
                                FROM ( SELECT CG_Extrude(ST_Buffer(ST_GeomFromText('POINT(100 90)'),
                                50, 'quad_segs=2'),0,0,30) AS geom1,
                                CG_Extrude(ST_Buffer(ST_GeomFromText('POINT(80 80)'),
                                50, 'quad_segs=1'),0,0,30) AS geom2 ) As t;

Intersection of geom1 and geom2

3D linestrings and polygons

    SELECT ST_AsText(CG_3DIntersection(linestring, polygon)) As wkt
    FROM  ST_GeomFromText('LINESTRING Z (2 2 6,1.5 1.5 7,1 1 8,0.5 0.5 8,0 0 10)') AS linestring
    CROSS JOIN ST_GeomFromText('POLYGON((0 0 8, 0 1 8, 1 1 8, 1 0 8, 0 0 8))') AS polygon;

    wkt
    --------------------------------
    LINESTRING Z (1 1 8,0.5 0.5 8)

Cube (closed Polyhedral Surface) and Polygon Z

SELECT ST_AsText(CG_3DIntersection(
ST_GeomFromText('POLYHEDRALSURFACE Z( ((0 0 0, 0 0 1, 0 1 1, 0 1 0, 0 0 0)),
((0 0 0, 0 1 0, 1 1 0, 1 0 0, 0 0 0)), ((0 0 0, 1 0 0, 1 0 1, 0 0 1, 0 0 0)),
((1 1 0, 1 1 1, 1 0 1, 1 0 0, 1 1 0)),
((0 1 0, 0 1 1, 1 1 1, 1 1 0, 0 1 0)), ((0 0 1, 1 0 1, 1 1 1, 0 1 1, 0 0 1)) )'),
'POLYGON Z ((0 0 0, 0 0 0.5, 0 0.5 0.5, 0 0.5 0, 0 0 0))'::geometry))

TIN Z (((0 0 0,0 0 0.5,0 0.5 0.5,0 0 0)),((0 0.5 0,0 0 0,0 0.5 0.5,0 0.5 0)))

Intersection of 2 solids that result in volumetric intersection is also a solid (ST_Dimension returns 3)

SELECT ST_AsText(CG_3DIntersection( CG_Extrude(ST_Buffer('POINT(10 20)'::geometry,10,1),0,0,30),
            CG_Extrude(ST_Buffer('POINT(10 20)'::geometry,10,1),2,0,10) ));

POLYHEDRALSURFACE Z (((13.3333333333333 13.3333333333333 10,20 20 0,20 20 10,13.3333333333333 13.3333333333333 10)),
        ((20 20 10,16.6666666666667 23.3333333333333 10,13.3333333333333 13.3333333333333 10,20 20 10)),
        ((20 20 0,16.6666666666667 23.3333333333333 10,20 20 10,20 20 0)),
        ((13.3333333333333 13.3333333333333 10,10 10 0,20 20 0,13.3333333333333 13.3333333333333 10)),
        ((16.6666666666667 23.3333333333333 10,12 28 10,13.3333333333333 13.3333333333333 10,16.6666666666667 23.3333333333333 10)),
        ((20 20 0,9.99999999999995 30 0,16.6666666666667 23.3333333333333 10,20 20 0)),
        ((10 10 0,9.99999999999995 30 0,20 20 0,10 10 0)),((13.3333333333333 13.3333333333333 10,12 12 10,10 10 0,13.3333333333333 13.3333333333333 10)),
        ((12 28 10,12 12 10,13.3333333333333 13.3333333333333 10,12 28 10)),
        ((16.6666666666667 23.3333333333333 10,9.99999999999995 30 0,12 28 10,16.6666666666667 23.3333333333333 10)),
        ((10 10 0,0 20 0,9.99999999999995 30 0,10 10 0)),
        ((12 12 10,11 11 10,10 10 0,12 12 10)),((12 28 10,11 11 10,12 12 10,12 28 10)),
        ((9.99999999999995 30 0,11 29 10,12 28 10,9.99999999999995 30 0)),((0 20 0,2 20 10,9.99999999999995 30 0,0 20 0)),
        ((10 10 0,2 20 10,0 20 0,10 10 0)),((11 11 10,2 20 10,10 10 0,11 11 10)),((12 28 10,11 29 10,11 11 10,12 28 10)),
        ((9.99999999999995 30 0,2 20 10,11 29 10,9.99999999999995 30 0)),((11 11 10,11 29 10,2 20 10,11 11 10)))

CG_Union

Computes the union of two geometries

Synopsis

geometry CG_Union(geometry
                            geomA, geometry
                            geomB)

Description

Computes the union of two geometries.

Performed by the SFCGAL module

Note

NOTE: this function returns a geometry representing the union.

Availability: 3.5.0

Geometry Examples

SELECT CG_Union('POINT(.5 0)', 'LINESTRING(-1 0,1 0)');
                cg_union
                -----------
                LINESTRING(-1 0,0.5 0,1 0)
                (1 row)

ST_3DUnion

Perform 3D union.

Synopsis

geometry ST_3DUnion(geometry geom1, geometry geom2)
geometry ST_3DUnion(geometry set g1field)

Description

Warning

ST_3DUnion is deprecated as of 3.5.0. Use CG_3DUnion instead.

Availability: 2.2.0

Availability: 3.3.0 aggregate variant was added

SQL-MM IEC 13249-3: 5.1

Aggregate variant: returns a geometry that is the 3D union of a rowset of geometries. The ST_3DUnion() function is an "aggregate" function in the terminology of PostgreSQL. That means that it operates on rows of data, in the same way the SUM() and AVG() functions do and like most aggregates, it also ignores NULL geometries.

CG_3DUnion

Perform 3D union using postgis_sfcgal.

Synopsis

geometry CG_3DUnion(geometry geom1, geometry geom2)
geometry CG_3DUnion(geometry set g1field)

Description

Availability: 3.5.0

SQL-MM IEC 13249-3: 5.1

Aggregate variant: returns a geometry that is the 3D union of a rowset of geometries. The CG_3DUnion() function is an "aggregate" function in the terminology of PostgreSQL. That means that it operates on rows of data, in the same way the SUM() and AVG() functions do and like most aggregates, it also ignores NULL geometries.

Examples

3D images were generated using PostGIS ST_AsX3D and rendering in HTML using X3Dom HTML Javascript rendering library.

SELECT CG_Extrude(ST_Buffer(ST_GeomFromText('POINT(100 90)'),
                                    50, 'quad_segs=2'),0,0,30) AS geom1,
                                    CG_Extrude(ST_Buffer(ST_GeomFromText('POINT(80 80)'),
                                    50, 'quad_segs=1'),0,0,30) AS geom2;

Original 3D geometries overlaid. geom2 is the one with transparency.

SELECT CG_3DUnion(geom1,geom2)
                                FROM ( SELECT CG_Extrude(ST_Buffer(ST_GeomFromText('POINT(100 90)'),
                                50, 'quad_segs=2'),0,0,30) AS geom1,
                                CG_Extrude(ST_Buffer(ST_GeomFromText('POINT(80 80)'),
                                50, 'quad_segs=1'),0,0,30) AS geom2 ) As t;

Union of geom1 and geom2

ST_AlphaShape

Computes an Alpha-shape enclosing a geometry

Synopsis

geometry ST_AlphaShape(geometry geom, float  alpha, boolean  allow_holes = false)

Description

Warning

ST_AlphaShape is deprecated as of 3.5.0. Use CG_AlphaShape instead.

Computes the Alpha-Shape of the points in a geometry. An alpha-shape is a (usually) concave polygonal geometry which contains all the vertices of the input, and whose vertices are a subset of the input vertices. An alpha-shape provides a closer fit to the shape of the input than the shape produced by the convex hull.

CG_AlphaShape

Computes an Alpha-shape enclosing a geometry

Synopsis

geometry CG_AlphaShape(geometry geom, float  alpha, boolean  allow_holes = false)

Description

Computes the Alpha-Shape of the points in a geometry. An alpha-shape is a (usually) concave polygonal geometry which contains all the vertices of the input, and whose vertices are a subset of the input vertices. An alpha-shape provides a closer fit to the shape of the input than the shape produced by the convex hull.

The "closeness of fit" is controlled by the alpha parameter, which can have values from 0 to infinity. Smaller alpha values produce more concave results. Alpha values greater than some data-dependent value produce the convex hull of the input.

Note

Following the CGAL implementation, the alpha value is the square of the radius of the disc used in the Alpha-Shape algorithm to "erode" the Delaunay Triangulation of the input points. See CGAL Alpha-Shapes for more information. This is different from the original definition of alpha-shapes, which defines alpha as the radius of the eroding disc.

The computed shape does not contain holes unless the optional allow_holes argument is specified as true.

This function effectively computes a concave hull of a geometry in a similar way to ST_ConcaveHull, but uses CGAL and a different algorithm.

Availability: 3.5.0 - requires SFCGAL >= 1.4.1.

Examples

Alpha-shape of a MultiPoint (same example As CG_OptimalAlphaShape)

SELECT ST_AsText(CG_AlphaShape('MULTIPOINT((63 84),(76 88),(68 73),(53 18),(91 50),(81 70),
            (88 29),(24 82),(32 51),(37 23),(27 54),(84 19),(75 87),(44 42),(77 67),(90 30),(36 61),(32 65),
            (81 47),(88 58),(68 73),(49 95),(81 60),(87 50),
            (78 16),(79 21),(30 22),(78 43),(26 85),(48 34),(35 35),(36 40),(31 79),(83 29),(27 84),(52 98),(72 95),(85 71),
            (75 84),(75 77),(81 29),(77 73),(41 42),(83 72),(23 36),(89 53),(27 57),(57 97),(27 77),(39 88),(60 81),
            (80 72),(54 32),(55 26),(62 22),(70 20),(76 27),(84 35),(87 42),(82 54),(83 64),(69 86),(60 90),(50 86),(43 80),(36 73),
            (36 68),(40 75),(24 67),(23 60),(26 44),(28 33),(40 32),(43 19),(65 16),(73 16),(38 46),(31 59),(34 86),(45 90),(64 97))'::geometry,80.2));

POLYGON((89 53,91 50,87 42,90 30,88 29,84 19,78 16,73 16,65 16,53 18,43 19,
        37 23,30 22,28 33,23 36,26 44,27 54,23 60,24 67,27 77,
        24 82,26 85,34 86,39 88,45 90,49 95,52 98,57 97,
        64 97,72 95,76 88,75 84,83 72,85 71,88 58,89 53))

Alpha-shape of a MultiPoint, allowing holes (same example as CG_OptimalAlphaShape)

SELECT ST_AsText(CG_AlphaShape('MULTIPOINT((63 84),(76 88),(68 73),(53 18),(91 50),(81 70),(88 29),(24 82),(32 51),(37 23),(27 54),(84 19),(75 87),(44 42),(77 67),(90 30),(36 61),(32 65),(81 47),(88 58),(68 73),(49 95),(81 60),(87 50),
    (78 16),(79 21),(30 22),(78 43),(26 85),(48 34),(35 35),(36 40),(31 79),(83 29),(27 84),(52 98),(72 95),(85 71),
    (75 84),(75 77),(81 29),(77 73),(41 42),(83 72),(23 36),(89 53),(27 57),(57 97),(27 77),(39 88),(60 81),
    (80 72),(54 32),(55 26),(62 22),(70 20),(76 27),(84 35),(87 42),(82 54),(83 64),(69 86),(60 90),(50 86),(43 80),(36 73),
    (36 68),(40 75),(24 67),(23 60),(26 44),(28 33),(40 32),(43 19),(65 16),(73 16),(38 46),(31 59),(34 86),(45 90),(64 97))'::geometry, 100.1,true))

POLYGON((89 53,91 50,87 42,90 30,84 19,78 16,73 16,65 16,53 18,43 19,30 22,28 33,23 36,
26 44,27 54,23 60,24 67,27 77,24 82,26 85,34 86,39 88,45 90,49 95,52 98,57 97,64 97,72 95,
76 88,75 84,83 72,85 71,88 58,89 53),(36 61,36 68,40 75,43 80,60 81,68 73,77 67,
81 60,82 54,81 47,78 43,76 27,62 22,54 32,44 42,38 46,36 61))

Alpha-shape of a MultiPoint, allowing holes (same example as ST_ConcaveHull)

SELECT ST_AsText(CG_AlphaShape(
                'MULTIPOINT ((132 64), (114 64), (99 64), (81 64), (63 64), (57 49), (52 36), (46 20), (37 20), (26 20), (32 36), (39 55), (43 69), (50 84), (57 100), (63 118), (68 133), (74 149), (81 164), (88 180), (101 180), (112 180), (119 164), (126 149), (132 131), (139 113), (143 100), (150 84), (157 69), (163 51), (168 36), (174 20), (163 20), (150 20), (143 36), (139 49), (132 64), (99 151), (92 138), (88 124), (81 109), (74 93), (70 82), (83 82), (99 82), (112 82), (126 82), (121 96), (114 109), (110 122), (103 138), (99 151), (34 27), (43 31), (48 44), (46 58), (52 73), (63 73), (61 84), (72 71), (90 69), (101 76), (123 71), (141 62), (166 27), (150 33), (159 36), (146 44), (154 53), (152 62), (146 73), (134 76), (143 82), (141 91), (130 98), (126 104), (132 113), (128 127), (117 122), (112 133), (119 144), (108 147), (119 153), (110 171), (103 164), (92 171), (86 160), (88 142), (79 140), (72 124), (83 131), (79 118), (68 113), (63 102), (68 93), (35 45))'::geometry,102.2, true));

POLYGON((26 20,32 36,35 45,39 55,43 69,50 84,57 100,63 118,68 133,74 149,81 164,88 180,
            101 180,112 180,119 164,126 149,132 131,139 113,143 100,150 84,157 69,163 51,168 36,
            174 20,163 20,150 20,143 36,139 49,132 64,114 64,99 64,90 69,81 64,63 64,57 49,52 36,46 20,37 20,26 20),
            (74 93,81 109,88 124,92 138,103 138,110 122,114 109,121 96,112 82,99 82,83 82,74 93))

CG_ApproxConvexPartition

Computes approximal convex partition of the polygon geometry

Synopsis

geometry CG_ApproxConvexPartition(geometry geom)

Description

Computes approximal convex partition of the polygon geometry (using a triangulation).

Note

A partition of a polygon P is a set of polygons such that the interiors of the polygons do not intersect and the union of the polygons is equal to the interior of the original polygon P. CG_ApproxConvexPartition and CG_GreeneApproxConvexPartition functions produce approximately optimal convex partitions. Both these functions produce convex decompositions by first decomposing the polygon into simpler polygons; CG_ApproxConvexPartition uses a triangulation and CG_GreeneApproxConvexPartition a monotone partition. These two functions both guarantee that they will produce no more than four times the optimal number of convex pieces but they differ in their runtime complexities. Though the triangulation-based approximation algorithm often results in fewer convex pieces, this is not always the case.

Availability: 3.5.0 - requires SFCGAL >= 1.5.0.

Requires SFCGAL >= 1.5.0

Examples

Approximal Convex Partition (same example As CG_YMonotonePartition, CG_GreeneApproxConvexPartition and CG_OptimalConvexPartition)

SELECT ST_AsText(CG_ApproxConvexPartition('POLYGON((156 150,83 181,89 131,148 120,107 61,32 159,0 45,41 86,45 1,177 2,67 24,109 31,170 60,180 110,156 150))'::geometry));

GEOMETRYCOLLECTION(POLYGON((156 150,83 181,89 131,148 120,156 150)),POLYGON((32 159,0 45,41 86,32 159)),POLYGON((107 61,32 159,41 86,107 61)),POLYGON((45 1,177 2,67 24,45 1)),POLYGON((41 86,45 1,67 24,41 86)),POLYGON((107 61,41 86,67 24,109 31,107 61)),POLYGON((148 120,107 61,109 31,170 60,148 120)),POLYGON((156 150,148 120,170 60,180 110,156 150)))

ST_ApproximateMedialAxis

Compute the approximate medial axis of an areal geometry.

Synopsis

geometry ST_ApproximateMedialAxis(geometry geom)

Description

Warning

ST_ApproximateMedialAxis is deprecated as of 3.5.0. Use CG_ApproximateMedialAxis instead.

Return an approximate medial axis for the areal input based on its straight skeleton. Uses an SFCGAL specific API when built against a capable version (1.2.0+). Otherwise the function is just a wrapper around CG_StraightSkeleton (slower case).

Availability: 2.2.0

CG_ApproximateMedialAxis

Compute the approximate medial axis of an areal geometry.

Synopsis

geometry CG_ApproximateMedialAxis(geometry geom)

Description

Return an approximate medial axis for the areal input based on its straight skeleton. Uses an SFCGAL specific API when built against a capable version (1.2.0+). Otherwise the function is just a wrapper around CG_StraightSkeleton (slower case).

Availability: 3.5.0

Examples

SELECT CG_ApproximateMedialAxis(ST_GeomFromText('POLYGON (( 190 190, 10 190, 10 10, 190 10, 190 20, 160 30, 60 30, 60 130, 190 140, 190 190 ))'));

A polygon and its approximate medial axis

ST_ConstrainedDelaunayTriangles

Return a constrained Delaunay triangulation around the given input geometry.

Synopsis

geometry ST_ConstrainedDelaunayTriangles(geometry  g1)

Description

Warning

ST_ConstrainedDelaunayTriangles is deprecated as of 3.5.0. Use CG_ConstrainedDelaunayTriangles instead.

Return a Constrained Delaunay triangulation around the vertices of the input geometry. Output is a TIN.

Availability: 3.0.0

CG_ConstrainedDelaunayTriangles

Return a constrained Delaunay triangulation around the given input geometry.

Synopsis

geometry CG_ConstrainedDelaunayTriangles(geometry  g1)

Description

Return a Constrained Delaunay triangulation around the vertices of the input geometry. Output is a TIN.

Availability: 3.0.0

Examples

CG_ConstrainedDelaunayTriangles of 2 polygons


                                        select CG_ConstrainedDelaunayTriangles(
                                        ST_Union(
                                        'POLYGON((175 150, 20 40, 50 60, 125 100, 175 150))'::geometry,
                                        ST_Buffer('POINT(110 170)'::geometry, 20)
                                        )
                                        );

ST_DelaunayTriangles of 2 polygons. Triangle edges cross polygon boundaries.


                                        select ST_DelaunayTriangles(
                                        ST_Union(
                                        'POLYGON((175 150, 20 40, 50 60, 125 100, 175 150))'::geometry,
                                        ST_Buffer('POINT(110 170)'::geometry, 20)
                                        )
                                        );

ST_Extrude

Extrude a surface to a related volume

Synopsis

geometry ST_Extrude(geometry geom, float x, float y, float z)

Description

Warning

ST_Extrude is deprecated as of 3.5.0. Use CG_Extrude instead.

Availability: 2.1.0

CG_Extrude

Extrude a surface to a related volume

Synopsis

geometry CG_Extrude(geometry geom, float x, float y, float z)

Description

Availability: 3.5.0

Examples

3D images were generated using PostGIS ST_AsX3D and rendering in HTML using X3Dom HTML Javascript rendering library.

SELECT ST_Buffer(ST_GeomFromText('POINT(100 90)'),
                                    50, 'quad_segs=2'),0,0,30);

Original octagon formed from buffering point

CG_Extrude(ST_Buffer(ST_GeomFromText('POINT(100 90)'),
                                50, 'quad_segs=2'),0,0,30);

Hexagon extruded 30 units along Z produces a PolyhedralSurfaceZ

SELECT ST_GeomFromText('LINESTRING(50 50, 100 90, 95 150)')

Original linestring

SELECT CG_Extrude(
                            ST_GeomFromText('LINESTRING(50 50, 100 90, 95 150)'),0,0,10));

LineString Extruded along Z produces a PolyhedralSurfaceZ

CG_ExtrudeStraightSkeleton

Straight Skeleton Extrusion

Synopsis

geometry CG_ExtrudeStraightSkeleton(geometry geom, float  roof_height, float  body_height = 0)

Description

Computes an extrusion with a maximal height of the polygon geometry.

Note

Perhaps the first (historically) use-case of straight skeletons: given a polygonal roof, the straight skeleton directly gives the layout of each tent. If each skeleton edge is lifted from the plane a height equal to its offset distance, the resulting roof is "correct" in that water will always fall down to the contour edges (the roof's border), regardless of where it falls on the roof. The function computes this extrusion aka "roof" on a polygon. If the argument body_height > 0, so the polygon is extruded like with CG_Extrude(polygon, 0, 0, body_height). The result is an union of these polyhedralsurfaces.

Availability: 3.5.0 - requires SFCGAL >= 1.5.0.

Requires SFCGAL >= 1.5.0

Examples

SELECT ST_AsText(CG_ExtrudeStraightSkeleton('POLYGON (( 0 0, 5 0, 5 5, 4 5, 4 4, 0 4, 0 0 ), (1 1, 1 2,2 2, 2 1, 1 1))', 3.0, 2.0));

POLYHEDRALSURFACE Z (((0 0 0,0 4 0,4 4 0,4 5 0,5 5 0,5 0 0,0 0 0),(1 1 0,2 1 0,2 2 0,1 2 0,1 1 0)),((0 0 0,0 0 2,0 4 2,0 4 0,0 0 0)),((0 4 0,0 4 2,4 4 2,4 4 0,0 4 0)),((4 4 0,4 4 2,4 5 2,4 5 0,4 4 0)),((4 5 0,4 5 2,5 5 2,5 5 0,4 5 0)),((5 5 0,5 5 2,5 0 2,5 0 0,5 5 0)),((5 0 0,5 0 2,0 0 2,0 0 0,5 0 0)),((1 1 0,1 1 2,2 1 2,2 1 0,1 1 0)),((2 1 0,2 1 2,2 2 2,2 2 0,2 1 0)),((2 2 0,2 2 2,1 2 2,1 2 0,2 2 0)),((1 2 0,1 2 2,1 1 2,1 1 0,1 2 0)),((4 5 2,5 5 2,4 4 2,4 5 2)),((2 1 2,5 0 2,0 0 2,2 1 2)),((5 5 2,5 0 2,4 4 2,5 5 2)),((2 1 2,0 0 2,1 1 2,2 1 2)),((1 2 2,1 1 2,0 0 2,1 2 2)),((0 4 2,2 2 2,1 2 2,0 4 2)),((0 4 2,1 2 2,0 0 2,0 4 2)),((4 4 2,5 0 2,2 2 2,4 4 2)),((4 4 2,2 2 2,0 4 2,4 4 2)),((2 2 2,5 0 2,2 1 2,2 2 2)),((0.5 2.5 2.5,0 0 2,0.5 0.5 2.5,0.5 2.5 2.5)),((1 3 3,0 4 2,0.5 2.5 2.5,1 3 3)),((0.5 2.5 2.5,0 4 2,0 0 2,0.5 2.5 2.5)),((2.5 0.5 2.5,5 0 2,3.5 1.5 3.5,2.5 0.5 2.5)),((0 0 2,5 0 2,2.5 0.5 2.5,0 0 2)),((0.5 0.5 2.5,0 0 2,2.5 0.5 2.5,0.5 0.5 2.5)),((4.5 3.5 2.5,5 5 2,4.5 4.5 2.5,4.5 3.5 2.5)),((3.5 2.5 3.5,3.5 1.5 3.5,4.5 3.5 2.5,3.5 2.5 3.5)),((4.5 3.5 2.5,5 0 2,5 5 2,4.5 3.5 2.5)),((3.5 1.5 3.5,5 0 2,4.5 3.5 2.5,3.5 1.5 3.5)),((5 5 2,4 5 2,4.5 4.5 2.5,5 5 2)),((4.5 4.5 2.5,4 4 2,4.5 3.5 2.5,4.5 4.5 2.5)),((4.5 4.5 2.5,4 5 2,4 4 2,4.5 4.5 2.5)),((3 3 3,0 4 2,1 3 3,3 3 3)),((3.5 2.5 3.5,4.5 3.5 2.5,3 3 3,3.5 2.5 3.5)),((3 3 3,4 4 2,0 4 2,3 3 3)),((4.5 3.5 2.5,4 4 2,3 3 3,4.5 3.5 2.5)),((2 1 2,1 1 2,0.5 0.5 2.5,2 1 2)),((2.5 0.5 2.5,2 1 2,0.5 0.5 2.5,2.5 0.5 2.5)),((1 1 2,1 2 2,0.5 2.5 2.5,1 1 2)),((0.5 0.5 2.5,1 1 2,0.5 2.5 2.5,0.5 0.5 2.5)),((1 3 3,2 2 2,3 3 3,1 3 3)),((0.5 2.5 2.5,1 2 2,1 3 3,0.5 2.5 2.5)),((1 3 3,1 2 2,2 2 2,1 3 3)),((2 2 2,2 1 2,2.5 0.5 2.5,2 2 2)),((3.5 2.5 3.5,3 3 3,3.5 1.5 3.5,3.5 2.5 3.5)),((3.5 1.5 3.5,2 2 2,2.5 0.5 2.5,3.5 1.5 3.5)),((3 3 3,2 2 2,3.5 1.5 3.5,3 3 3)))

CG_GreeneApproxConvexPartition

Computes approximal convex partition of the polygon geometry

Synopsis

geometry CG_GreeneApproxConvexPartition(geometry geom)

Description

Computes approximal monotone convex partition of the polygon geometry.

Note

A partition of a polygon P is a set of polygons such that the interiors of the polygons do not intersect and the union of the polygons is equal to the interior of the original polygon P. CG_ApproxConvexPartition and CG_GreeneApproxConvexPartition functions produce approximately optimal convex partitions. Both these functions produce convex decompositions by first decomposing the polygon into simpler polygons; CG_ApproxConvexPartition uses a triangulation and CG_GreeneApproxConvexPartition a monotone partition. These two functions both guarantee that they will produce no more than four times the optimal number of convex pieces but they differ in their runtime complexities. Though the triangulation-based approximation algorithm often results in fewer convex pieces, this is not always the case.

Availability: 3.5.0 - requires SFCGAL >= 1.5.0.

Requires SFCGAL >= 1.5.0

Examples

Greene Approximal Convex Partition (same example As CG_YMonotonePartition, CG_ApproxConvexPartition and CG_OptimalConvexPartition)

SELECT ST_AsText(CG_GreeneApproxConvexPartition('POLYGON((156 150,83 181,89 131,148 120,107 61,32 159,0 45,41 86,45 1,177 2,67 24,109 31,170 60,180 110,156 150))'::geometry));

GEOMETRYCOLLECTION(POLYGON((32 159,0 45,41 86,32 159)),POLYGON((45 1,177 2,67 24,45 1)),POLYGON((67 24,109 31,170 60,107 61,67 24)),POLYGON((41 86,45 1,67 24,41 86)),POLYGON((107 61,32 159,41 86,67 24,107 61)),POLYGON((148 120,107 61,170 60,148 120)),POLYGON((148 120,170 60,180 110,156 150,148 120)),POLYGON((156 150,83 181,89 131,148 120,156 150)))

ST_MinkowskiSum

Performs Minkowski sum

Synopsis

geometry ST_MinkowskiSum(geometry geom1, geometry geom2)

Description

Warning

ST_MinkowskiSum is deprecated as of 3.5.0. Use CG_MinkowskiSum instead.

This function performs a 2D minkowski sum of a point, line or polygon with a polygon.

A minkowski sum of two geometries A and B is the set of all points that are the sum of any point in A and B. Minkowski sums are often used in motion planning and computer-aided design. More details on Wikipedia Minkowski addition.

The first parameter can be any 2D geometry (point, linestring, polygon). If a 3D geometry is passed, it will be converted to 2D by forcing Z to 0, leading to possible cases of invalidity. The second parameter must be a 2D polygon.

Implementation utilizes CGAL 2D Minkowskisum.

Availability: 2.1.0

CG_MinkowskiSum

Performs Minkowski sum

Synopsis

geometry CG_MinkowskiSum(geometry geom1, geometry geom2)

Description

This function performs a 2D minkowski sum of a point, line or polygon with a polygon.

A minkowski sum of two geometries A and B is the set of all points that are the sum of any point in A and B. Minkowski sums are often used in motion planning and computer-aided design. More details on Wikipedia Minkowski addition.

The first parameter can be any 2D geometry (point, linestring, polygon). If a 3D geometry is passed, it will be converted to 2D by forcing Z to 0, leading to possible cases of invalidity. The second parameter must be a 2D polygon.

Implementation utilizes CGAL 2D Minkowskisum.

Availability: 3.5.0

Examples

Minkowski Sum of Linestring and circle polygon where Linestring cuts thru the circle

Before Summing

After summing

            SELECT CG_MinkowskiSum(line, circle))
            FROM (SELECT
            ST_MakeLine(ST_Point(10, 10),ST_Point(100, 100)) As line,
            ST_Buffer(ST_GeomFromText('POINT(50 50)'), 30) As circle) As foo;

            -- wkt --
            MULTIPOLYGON(((30 59.9999999999999,30.5764415879031 54.1472903395161,32.2836140246614 48.5194970290472,35.0559116309237 43.3328930094119,38.7867965644036 38.7867965644035,43.332893009412 35.0559116309236,48.5194970290474 32.2836140246614,54.1472903395162 30.5764415879031,60.0000000000001 30,65.8527096604839 30.5764415879031,71.4805029709527 32.2836140246614,76.6671069905881 35.0559116309237,81.2132034355964 38.7867965644036,171.213203435596 128.786796564404,174.944088369076 133.332893009412,177.716385975339 138.519497029047,179.423558412097 144.147290339516,180 150,179.423558412097 155.852709660484,177.716385975339 161.480502970953,174.944088369076 166.667106990588,171.213203435596 171.213203435596,166.667106990588 174.944088369076,
            161.480502970953 177.716385975339,155.852709660484 179.423558412097,150 180,144.147290339516 179.423558412097,138.519497029047 177.716385975339,133.332893009412 174.944088369076,128.786796564403 171.213203435596,38.7867965644035 81.2132034355963,35.0559116309236 76.667106990588,32.2836140246614 71.4805029709526,30.5764415879031 65.8527096604838,30 59.9999999999999)))

Minkowski Sum of a polygon and multipoint

Before Summing

After summing: polygon is duplicated and translated to position of points

SELECT CG_MinkowskiSum(mp, poly)
        FROM (SELECT 'MULTIPOINT(25 50,70 25)'::geometry As mp,
        'POLYGON((130 150, 20 40, 50 60, 125 100, 130 150))'::geometry As poly
        ) As foo


        -- wkt --
        MULTIPOLYGON(
        ((70 115,100 135,175 175,225 225,70 115)),
        ((120 65,150 85,225 125,275 175,120 65))
        )

ST_OptimalAlphaShape

Computes an Alpha-shape enclosing a geometry using an "optimal" alpha value.

Synopsis

geometry ST_OptimalAlphaShape(geometry geom, boolean  allow_holes = false, integer  nb_components = 1)

Description

Warning

ST_OptimalAlphaShape is deprecated as of 3.5.0. Use CG_OptimalAlphaShape instead.

Computes the "optimal" alpha-shape of the points in a geometry. The alpha-shape is computed using a value of α chosen so that:

the number of polygon elements is equal to or smaller than nb_components (which defaults to 1)
all input points are contained in the shape

The result will not contain holes unless the optional allow_holes argument is specified as true.

Availability: 3.3.0 - requires SFCGAL >= 1.4.1.

CG_OptimalAlphaShape

Computes an Alpha-shape enclosing a geometry using an "optimal" alpha value.

Synopsis

geometry CG_OptimalAlphaShape(geometry geom, boolean  allow_holes = false, integer  nb_components = 1)

Description

Computes the "optimal" alpha-shape of the points in a geometry. The alpha-shape is computed using a value of α chosen so that:

the number of polygon elements is equal to or smaller than nb_components (which defaults to 1)
all input points are contained in the shape

The result will not contain holes unless the optional allow_holes argument is specified as true.

Availability: 3.5.0 - requires SFCGAL >= 1.4.1.

Examples

Optimal alpha-shape of a MultiPoint (same example as CG_AlphaShape)

SELECT ST_AsText(CG_OptimalAlphaShape('MULTIPOINT((63 84),(76 88),(68 73),(53 18),(91 50),(81 70),
                (88 29),(24 82),(32 51),(37 23),(27 54),(84 19),(75 87),(44 42),(77 67),(90 30),(36 61),(32 65),
                (81 47),(88 58),(68 73),(49 95),(81 60),(87 50),
                (78 16),(79 21),(30 22),(78 43),(26 85),(48 34),(35 35),(36 40),(31 79),(83 29),(27 84),(52 98),(72 95),(85 71),
                (75 84),(75 77),(81 29),(77 73),(41 42),(83 72),(23 36),(89 53),(27 57),(57 97),(27 77),(39 88),(60 81),
                (80 72),(54 32),(55 26),(62 22),(70 20),(76 27),(84 35),(87 42),(82 54),(83 64),(69 86),(60 90),(50 86),(43 80),(36 73),
                (36 68),(40 75),(24 67),(23 60),(26 44),(28 33),(40 32),(43 19),(65 16),(73 16),(38 46),(31 59),(34 86),(45 90),(64 97))'::geometry));

POLYGON((89 53,91 50,87 42,90 30,88 29,84 19,78 16,73 16,65 16,53 18,43 19,37 23,30 22,28 33,23 36,
            26 44,27 54,23 60,24 67,27 77,24 82,26 85,34 86,39 88,45 90,49 95,52 98,57 97,64 97,72 95,76 88,75 84,75 77,83 72,85 71,83 64,88 58,89 53))

Optimal alpha-shape of a MultiPoint, allowing holes (same example as CG_AlphaShape)

SELECT ST_AsText(CG_OptimalAlphaShape('MULTIPOINT((63 84),(76 88),(68 73),(53 18),(91 50),(81 70),(88 29),(24 82),(32 51),(37 23),(27 54),(84 19),(75 87),(44 42),(77 67),(90 30),(36 61),(32 65),(81 47),(88 58),(68 73),(49 95),(81 60),(87 50),
        (78 16),(79 21),(30 22),(78 43),(26 85),(48 34),(35 35),(36 40),(31 79),(83 29),(27 84),(52 98),(72 95),(85 71),
        (75 84),(75 77),(81 29),(77 73),(41 42),(83 72),(23 36),(89 53),(27 57),(57 97),(27 77),(39 88),(60 81),
        (80 72),(54 32),(55 26),(62 22),(70 20),(76 27),(84 35),(87 42),(82 54),(83 64),(69 86),(60 90),(50 86),(43 80),(36 73),
        (36 68),(40 75),(24 67),(23 60),(26 44),(28 33),(40 32),(43 19),(65 16),(73 16),(38 46),(31 59),(34 86),(45 90),(64 97))'::geometry, allow_holes => true));

POLYGON((89 53,91 50,87 42,90 30,88 29,84 19,78 16,73 16,65 16,53 18,43 19,37 23,30 22,28 33,23 36,26 44,27 54,23 60,24 67,27 77,24 82,26 85,34 86,39 88,45 90,49 95,52 98,57 97,64 97,72 95,76 88,75 84,75 77,83 72,85 71,83 64,88 58,89 53),(36 61,36 68,40 75,43 80,50 86,60 81,68 73,77 67,81 60,82 54,81 47,78 43,81 29,76 27,70 20,62 22,55 26,54 32,48 34,44 42,38 46,36 61))

CG_OptimalConvexPartition

Computes an optimal convex partition of the polygon geometry

Synopsis

geometry CG_OptimalConvexPartition(geometry geom)

Description

Computes an optimal convex partition of the polygon geometry.

Note

A partition of a polygon P is a set of polygons such that the interiors of the polygons do not intersect and the union of the polygons is equal to the interior of the original polygon P. CG_OptimalConvexPartition produces a partition that is optimal in the number of pieces.

Availability: 3.5.0 - requires SFCGAL >= 1.5.0.

Requires SFCGAL >= 1.5.0

Examples

Optimal Convex Partition (same example As CG_YMonotonePartition, CG_ApproxConvexPartition and CG_GreeneApproxConvexPartition)

SELECT ST_AsText(CG_OptimalConvexPartition('POLYGON((156 150,83 181,89 131,148 120,107 61,32 159,0 45,41 86,45 1,177 2,67 24,109 31,170 60,180 110,156 150))'::geometry));

GEOMETRYCOLLECTION(POLYGON((156 150,83 181,89 131,148 120,156 150)),POLYGON((32 159,0 45,41 86,32 159)),POLYGON((45 1,177 2,67 24,45 1)),POLYGON((41 86,45 1,67 24,41 86)),POLYGON((107 61,32 159,41 86,67 24,109 31,107 61)),POLYGON((148 120,107 61,109 31,170 60,180 110,148 120)),POLYGON((156 150,148 120,180 110,156 150)))

CG_StraightSkeleton

Compute a straight skeleton from a geometry

Synopsis

geometry CG_StraightSkeleton(geometry geom, boolean  use_distance_as_m = false)

Description

Availability: 3.5.0

Requires SFCGAL >= 1.3.8 for option use_distance_as_m

Examples

SELECT CG_StraightSkeleton(ST_GeomFromText('POLYGON (( 190 190, 10 190, 10 10, 190 10, 190 20, 160 30, 60 30, 60 130, 190 140, 190 190 ))'));

ST_AsText(CG_StraightSkeleton('POLYGON((0 0,1 0,1 1,0 1,0 0))', true);

MULTILINESTRING M ((0 0 0,0.5 0.5 0.5),(1 0 0,0.5 0.5 0.5),(1 1 0,0.5 0.5 0.5),(0 1 0,0.5 0.5 0.5))

Original polygon

Straight Skeleton of polygon

ST_StraightSkeleton

Compute a straight skeleton from a geometry

Synopsis

geometry ST_StraightSkeleton(geometry geom)

Description

Warning

ST_StraightSkeleton is deprecated as of 3.5.0. Use CG_StraightSkeleton instead.

Availability: 2.1.0

Examples

SELECT ST_StraightSkeleton(ST_GeomFromText('POLYGON (( 190 190, 10 190, 10 10, 190 10, 190 20, 160 30, 60 30, 60 130, 190 140, 190 190 ))'));

Original polygon

Straight Skeleton of polygon

ST_Tesselate

Perform surface Tessellation of a polygon or polyhedralsurface and returns as a TIN or collection of TINS

Synopsis

geometry ST_Tesselate(geometry geom)

Description

Warning

ST_Tesselate is deprecated as of 3.5.0. Use CG_Tesselate instead.

Takes as input a surface such a MULTI(POLYGON) or POLYHEDRALSURFACE and returns a TIN representation via the process of tessellation using triangles.

Note

ST_TriangulatePolygon does similar to this function except that it returns a geometry collection of polygons instead of a TIN and also only works with 2D geometries.

Availability: 2.1.0

CG_Tesselate

Perform surface Tessellation of a polygon or polyhedralsurface and returns as a TIN or collection of TINS

Synopsis

geometry CG_Tesselate(geometry geom)

Description

Takes as input a surface such a MULTI(POLYGON) or POLYHEDRALSURFACE and returns a TIN representation via the process of tessellation using triangles.

Note

ST_TriangulatePolygon does similar to this function except that it returns a geometry collection of polygons instead of a TIN and also only works with 2D geometries.

Availability: 3.5.0

Examples

SELECT ST_GeomFromText('POLYHEDRALSURFACE Z( ((0 0 0, 0 0 1, 0 1 1, 0 1 0, 0 0 0)),
                                    ((0 0 0, 0 1 0, 1 1 0, 1 0 0, 0 0 0)), ((0 0 0, 1 0 0, 1 0 1, 0 0 1, 0 0 0)),
                                    ((1 1 0, 1 1 1, 1 0 1, 1 0 0, 1 1 0)),
                                    ((0 1 0, 0 1 1, 1 1 1, 1 1 0, 0 1 0)), ((0 0 1, 1 0 1, 1 1 1, 0 1 1, 0 0 1)) )');

Original Cube

SELECT CG_Tesselate(ST_GeomFromText('POLYHEDRALSURFACE Z( ((0 0 0, 0 0 1, 0 1 1, 0 1 0, 0 0 0)),
                                ((0 0 0, 0 1 0, 1 1 0, 1 0 0, 0 0 0)), ((0 0 0, 1 0 0, 1 0 1, 0 0 1, 0 0 0)),
                                ((1 1 0, 1 1 1, 1 0 1, 1 0 0, 1 1 0)),
                                ((0 1 0, 0 1 1, 1 1 1, 1 1 0, 0 1 0)), ((0 0 1, 1 0 1, 1 1 1, 0 1 1, 0 0 1)) )'));

ST_AsText output:

TIN Z (((0 0 0,0 0 1,0 1 1,0 0 0)),((0 1 0,0 0 0,0 1 1,0 1 0)),
                        ((0 0 0,0 1 0,1 1 0,0 0 0)),
                        ((1 0 0,0 0 0,1 1 0,1 0 0)),((0 0 1,1 0 0,1 0 1,0 0 1)),
                        ((0 0 1,0 0 0,1 0 0,0 0 1)),
                        ((1 1 0,1 1 1,1 0 1,1 1 0)),((1 0 0,1 1 0,1 0 1,1 0 0)),
                        ((0 1 0,0 1 1,1 1 1,0 1 0)),((1 1 0,0 1 0,1 1 1,1 1 0)),
                        ((0 1 1,1 0 1,1 1 1,0 1 1)),((0 1 1,0 0 1,1 0 1,0 1 1)))

Tessellated Cube with triangles colored

SELECT 'POLYGON (( 10 190, 10 70, 80 70, 80 130, 50 160, 120 160, 120 190, 10 190 ))'::geometry;

Original polygon

SELECT
                        CG_Tesselate('POLYGON (( 10 190, 10 70, 80 70, 80 130, 50 160, 120 160, 120 190, 10 190 ))'::geometry);

ST_AsText output

TIN(((80 130,50 160,80 70,80 130)),((50 160,10 190,10 70,50 160)),
                ((80 70,50 160,10 70,80 70)),((120 160,120 190,50 160,120 160)),
                ((120 190,10 190,50 160,120 190)))

Tessellated Polygon

CG_Triangulate

Triangulates a polygonal geometry

Synopsis

geometry CG_Triangulate(geometry
                            geom)

Description

Triangulates a polygonal geometry.

Performed by the SFCGAL module

Note

NOTE: this function returns a geometry representing the triangulated result.

Availability: 3.5.0

Geometry Examples

SELECT CG_Triangulate('POLYGON((0.0 0.0,1.0 0.0,1.0 1.0,0.0 1.0,0.0 0.0),(0.2 0.2,0.2 0.8,0.8 0.8,0.8 0.2,0.2 0.2))');
                cg_triangulate
                ----------------
                TIN(((0.8 0.2,0.2 0.2,1 0,0.8 0.2)),((0.2 0.2,0 0,1 0,0.2 0.2)),((1 1,0.8 0.8,0.8 0.2,1 1)),((0 1,0 0,0.2 0.2,0 1)),((0 1,0.2 0.8,1 1,0 1)),((0 1,0.2 0.2,0.2 0.8,0 1)),((0.2 0.8,0.8 0.8,1 1,0.2 0.8)),((0.2 0.8,0.2 0.2,0.8 0.2,0.2 0.8)),((1 1,0.8 0.2,1 0,1 1)),((0.8 0.8,0.2 0.8,0.8 0.2,0.8 0.8)))

                (1 row)

CG_Visibility

Compute a visibility polygon from a point or a segment in a polygon geometry

Synopsis

geometry CG_Visibility(geometry polygon, geometry point)
geometry CG_Visibility(geometry polygon, geometry pointA, geometry pointB)

Description

Availability: 3.5.0 - requires SFCGAL >= 1.5.0.

Requires SFCGAL >= 1.5.0

Examples

SELECT CG_Visibility('POLYGON((23.5 23.5,23.5 173.5,173.5 173.5,173.5 23.5,23.5 23.5),(108 98,108 36,156 37,155 99,108 98),(107 157.5,107 106.5,135 107.5,133 127.5,143.5 127.5,143.5 108.5,153.5 109.5,151.5 166,107 157.5),(41 95.5,41 35,100.5 36,98.5 68,78.5 68,77.5 96.5,41 95.5),(39 150,40 104,97.5 106.5,95.5 152,39 150))'::geometry, 'POINT(91 87)'::geometry);

SELECT CG_Visibility('POLYGON((23.5 23.5,23.5 173.5,173.5 173.5,173.5 23.5,23.5 23.5),(108 98,108 36,156 37,155 99,108 98),(107 157.5,107 106.5,135 107.5,133 127.5,143.5 127.5,143.5 108.5,153.5 109.5,151.5 166,107 157.5),(41 95.5,41 35,100.5 36,98.5 68,78.5 68,77.5 96.5,41 95.5),(39 150,40 104,97.5 106.5,95.5 152,39 150))'::geometry,'POINT(78.5 68)'::geometry, 'POINT(98.5 68)'::geometry);

Original polygon

Visibility from the point

Visibility from the segment

CG_YMonotonePartition

Computes y-monotone partition of the polygon geometry

Synopsis

geometry CG_YMonotonePartition(geometry geom)

Description

Computes y-monotone partition of the polygon geometry.

Note

A partition of a polygon P is a set of polygons such that the interiors of the polygons do not intersect and the union of the polygons is equal to the interior of the original polygon P. A y-monotone polygon is a polygon whose vertices v1,…,vn can be divided into two chains v1,…,vk and vk,…,vn,v1, such that any horizontal line intersects either chain at most once. This algorithm does not guarantee a bound on the number of polygons produced with respect to the optimal number.

Availability: 3.5.0 - requires SFCGAL >= 1.5.0.

Requires SFCGAL >= 1.5.0

Examples

Original polygon

Y-Monotone Partition (same example As CG_ApproxConvexPartition, CG_GreeneApproxConvexPartition and CG_OptimalConvexPartition)

SELECT ST_AsText(CG_YMonotonePartition('POLYGON((156 150,83 181,89 131,148 120,107 61,32 159,0 45,41 86,45 1,177 2,67 24,109 31,170 60,180 110,156 150))'::geometry));

GEOMETRYCOLLECTION(POLYGON((32 159,0 45,41 86,32 159)),POLYGON((107 61,32 159,41 86,45 1,177 2,67 24,109 31,170 60,107 61)),POLYGON((156 150,83 181,89 131,148 120,107 61,170 60,180 110,156 150)))

SFCGAL Processing and Relationship Functions

CG_Intersection

Synopsis

Description

Geometry Examples

See Also

CG_Intersects

Synopsis

Description

Geometry Examples

See Also

CG_3DIntersects

Synopsis

Description

Geometry Examples

See Also

CG_Difference

Synopsis

Description

Geometry Examples

See Also

ST_3DDifference

Synopsis

Description

CG_3DDifference

Synopsis

Description

Examples

See Also

CG_Distance

Synopsis

Description

Geometry Examples

See Also

CG_3DDistance

Synopsis

Description

Geometry Examples

See Also

ST_3DConvexHull

Synopsis

Description

CG_3DConvexHull

Synopsis

Description

Examples

See Also

ST_3DIntersection

Synopsis

Description

CG_3DIntersection

Synopsis

Description

Examples

CG_Union

Synopsis

Description

Geometry Examples

See Also

ST_3DUnion

Synopsis

Description

CG_3DUnion

Synopsis

Description

Examples

See Also

ST_AlphaShape

Synopsis

Description

CG_AlphaShape

Synopsis

Description

Examples

See Also

CG_ApproxConvexPartition

Synopsis

Description

Examples

See Also