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Operation functions

Use operation functions to perform operations on geometry data type values. For example, you can obtain the boundaries of a single geometry data type; intersections between two geometry data types; difference between left and right geometries, where each is of the same geometry data type; or an exterior buffer or ring around a particular geometry data type.

geometry_union(array(geometry))

Returns a geometry that represents the point set union of the specified geometries. Example:

SELECT geometry_union(ARRAY[ST_Point(-158.54, 61.56), ST_Point(-158.55, 61.56)])

ST_Boundary(geometry)

Takes as an input one of the geometry data types and returns the boundary geometry data type.

Examples:

SELECT ST_Boundary(ST_Line('linestring(0 1, 1 0)')))

SELECT ST_Boundary(ST_Polygon('polygon((1  1, 1  4, 4  4, 4 1))'))

ST_Buffer(geometry, double)

Takes as an input one of the geometry data types, such as point, line, polygon, multiline, or multipolygon, and a distance as type double). Returns the geometry data type buffered by the specified distance (or radius). Example:

SELECT ST_Buffer(ST_Point(1, 2), 2.0)

In the following example, the map coordinates are specified in longitude and latitude, and the value .072284, which is the buffer distance, is specified in angular units as decimal degrees:

SELECT ST_Buffer(ST_Point(-74.006801, 40.705220), .072284)

ST_Difference(geometry, geometry)

Returns a geometry of the difference between the left geometry and right geometry. Example:

SELECT ST_AsText(ST_Difference(ST_Polygon('polygon((0 0, 0 10, 10 10, 10 0))'), ST_Polygon('polygon((0 0, 0 5, 5 5, 5 0))')))

ST_Envelope(geometry)

Takes as an input line, polygon, multiline, and multipolygon geometry data types. Does not support point geometry data type. Returns the envelope as a geometry, where an envelope is a rectangle around the specified geometry data type. Examples:

SELECT ST_Envelope(ST_Line('linestring(0 1, 1 0)'))

SELECT ST_Envelope(ST_Polygon('polygon((1  1, 1  4, 4  4, 4 1))'))

ST_EnvelopeAsPts(geometry)

Returns an array of two points that represent the lower left and upper right corners of a geometry's bounding rectangular polygon. Returns null if the specified geometry is empty. Example:

SELECT ST_EnvelopeAsPts(ST_Point(-158.54, 61.56))

ST_ExteriorRing(geometry)

Returns the geometry of the exterior ring of the input type polygon. Starting in Athena engine version 2, polygons are the only geometries accepted as inputs. Examples:

SELECT ST_ExteriorRing(ST_Polygon(1,1, 1,4, 4,1))

SELECT ST_ExteriorRing(ST_Polygon('polygon ((0 0, 8 0, 0 8, 0 0), (1 1, 1 5, 5 1, 1 1))'))

ST_Intersection(geometry, geometry)

Returns the geometry of the intersection of the left geometry and right geometry. Examples:

SELECT ST_Intersection(ST_Point(1,1), ST_Point(1,1))

SELECT ST_Intersection(ST_Line('linestring(0 1, 1 0)'), ST_Polygon('polygon((1  1, 1  4, 4  4, 4 1))'))

SELECT ST_AsText(ST_Intersection(ST_Polygon('polygon((2 0, 2 3, 3 0))'), ST_Polygon('polygon((1 1, 4 1, 4 4, 1 4))')))

ST_SymDifference(geometry, geometry)

Returns the geometry of the geometrically symmetric difference between the left geometry and the right geometry. Example:

SELECT ST_AsText(ST_SymDifference(ST_Line('linestring(0 2, 2 2)'), ST_Line('linestring(1 2, 3 2)')))

ST_Union(geometry, geometry)

Returns a geometry data type that represents the point set union of the specified geometries. Example:

SELECT ST_Union(ST_Point(-158.54, 61.56),ST_LineString(array[ST_Point(1,2), ST_Point(3,4)]))