OpenGIS Functions

AddGeometryColumn(varchar, varchar, varchar, integer, varchar, integer)

Syntax: AddGeometryColumn(<db_name>, <table_name>, <column_name>, <srid>, <type>, <dimension>). Adds a geometry column to an existing table of attributes. The dbname is the name of the database instance. The srid must be an integer value reference to an entry in the SPATIAL_REF_SYS table. The type must be an uppercase string corresponding to the geometry type, eg, 'POLYGON' or 'MULTILINESTRING'.

DropGeometryColumn(varchar, varchar, varchar)

Syntax: DropGeometryColumn(<db_name>, <table_name>, <column_name>). Remove a geometry column from a spatial table.

AsBinary(geometry)

Returns the geometry in the OGC "well-known-binary" format, using the endian encoding of the server on which the database is running. This is useful in binary cursors to pull data out of the database without converting it to a string representation.

OGC SPEC s2.1.1.1 - also see asBinary(<geometry>,'XDR') and asBinary(<geometry>,'NDR')

Dimension(geometry)

The inherent dimension of this Geometry object, which must be less than or equal to the coordinate dimension. OGC SPEC s2.1.1.1 - returns 0 for points, 1 for lines, 2 for polygons, and the largest dimension of the components of a GEOMETRYCOLLECTION.

select dimension('GEOMETRYCOLLECTION(LINESTRING(1 1,0 0),POINT(0 0)'); 
dimension 
-----------
1

isEmpty(geometry)

Returns 1 (TRUE) if this Geometry is the empty geometry . If true, then this Geometry represents the empty point set - i.e. GEOMETRYCOLLECTION(EMPTY).

OGC SPEC s2.1.1.1

isSimple(geometry)

Returns 1 (TRUE) if this Geometry has no anomalous geometric points, such as self intersection or self tangency.

Performed by the GEOS module

OGC SPEC s2.1.1.1

boundary(geometry)

Returns the closure of the combinatorial boundary of this Geometry. The combinatorial boundary is defined as described in section 3.12.3.2 of the OGC SPEC. Because the result of this function is a closure, and hence topologically closed, the resulting boundary can be represented using representational geometry primitives as discussed in the OGC SPEC, section 3.12.2.

Performed by the GEOS module

OGC SPEC s2.1.1.1

equals(geometry)

Returns 1 (TRUE) if this Geometry is "spatially equal" to anotherGeometry. Use this for a 'better' answer than '='. equals ('LINESTRING(0 0, 10 10)','LINESTRING(0 0, 5 5, 10 10)') is true.

Performed by the GEOS module

OGC SPEC s2.1.1.1

disjoint(geometry,geometry)

Returns 1 (TRUE) if this Geometry is "spatially disjoint" from anotherGeometry.

Performed by the GEOS module

Do not call with a GeometryCollection as an argument

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

OGC SPEC s2.1.1.1 //s2.1.13.3 - a.Relate(b, 'FF*FF****')

intersects(geometry,geometry)

Returns 1 (TRUE) if this Geometry "spatially intersects" anotherGeometry.

Performed by the GEOS module

Do not call with a GeometryCollection as an argument

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

OGC SPEC s2.1.1.1 //s2.1.13.3 - Intersects(g1, g2 ) --> Not (Disjoint(g1, g2 ))

touches(geometry,geometry)

Returns 1 (TRUE) if this Geometry "spatially touches" anotherGeometry.

Performed by the GEOS module

Do not call with a GeometryCollection as an argument

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

OGC SPEC s2.1.1.1 // s2.1.13.3- a.Touches(b) -> (I(a) intersection I(b) = {empty set} ) and (a intersection b) not empty

crosses(geometry,geometry)

Returns 1 (TRUE) if this Geometry "spatially crosses" anotherGeometry.

Performed by the GEOS module

Do not call with a GeometryCollection as an argument

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

OGC SPEC s2.1.1.1 // s2.1.13.3 - a.Relate(b, 'T*T******')

within(geometry,geometry)

Returns 1 (TRUE) if this Geometry is "spatially within" anotherGeometry.

Performed by the GEOS module

Do not call with a GeometryCollection as an argument

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

OGC SPEC s2.1.1.1 // s2.1.13.3 - a.Relate(b, 'T*F**F***')

overlaps(geometry,geometry)

Returns 1 (TRUE) if this Geometry is "spatially overlapping" anotherGeometry.

Performed by the GEOS module

Do not call with a GeometryCollection as an argument

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

OGC SPEC s2.1.1.1 // s2.1.13.3

contains(geometry,geometry)

Returns 1 (TRUE) if this Geometry is "spatially contains" anotherGeometry.

Performed by the GEOS module

Do not call with a GeometryCollection as an argument

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

OGC SPEC s2.1.1.1 // s2.1.13.3 - same as within(geometry,geometry)

intersects(geometry,geometry)

Returns 1 (TRUE) if this Geometry is "spatially intersects" anotherGeometry.

Performed by the GEOS module

Do not call with a GeometryCollection as an argument

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

OGC SPEC s2.1.1.1 // s2.1.13.3 - NOT disjoint(geometry,geometry)

relate(geometry,geometry, intersectionPatternMatrix)

Returns 1 (TRUE) if this Geometry is spatially related to anotherGeometry, by testing for intersections between the Interior, Boundary and Exterior of the two geometries as specified by the values in the intersectionPatternMatrix.

Performed by the GEOS module

Do not call with a GeometryCollection as an argument

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

OGC SPEC s2.1.1.1 // s2.1.13.3

relate(geometry,geometry)

returns the DE-9IM (dimensionally extended nine-intersection matrix)

Performed by the GEOS module

Do not call with a GeometryCollection as an argument

not in OGC spec, but implied. see s2.1.13.2

buffer(geometry,double)

Returns a geometry that represents all points whose distance from this Geometry is less than or equal to distance. Calculations are in the Spatial Reference System of this Geometry.

Performed by the GEOS module

Do not call with a GeometryCollection as an argument

OGC SPEC s2.1.1.1

convexhull(geometry)

Returns a geometry that represents the convex hull of this Geometry.

Performed by the GEOS module

OGC SPEC s2.1.1.1

intersection(geometry,geometry)

Returns a geometry that represents the point set intersection of this Geometry with anotherGeometry.

Performed by the GEOS module

Do not call with a GeometryCollection as an argument

OGC SPEC s2.1.1.1

GeomUnion(geometry,geometry)

Returns a geometry that represents the point set union of this Geometry with anotherGeometry.

Performed by the GEOS module

Do not call with a GeometryCollection as an argument

NOTE: this is renamed from "union" because union is an SQL reserved word

OGC SPEC s2.1.1.1

GeomUnion(geometry set)

Returns a geometry that represents the point set union of this all Geometries in given set.

Performed by the GEOS module

Do not call with a GeometryCollection in the argument set

Not explicitly defined in OGC SPEC

memGeomUnion(geometry set)

Same as the above, only memory-friendly (uses less memory and more processor time).

difference(geometry,geometry)

Returns a geometry that represents the point set difference of this Geometry with anotherGeometry.

Performed by the GEOS module

Do not call with a GeometryCollection as an argument

OGC SPEC s2.1.1.1

difference(geometry,geometry)

Returns a geometry that represents the point set symmetric difference of this Geometry with anotherGeometry.

Performed by the GEOS module

Do not call with a GeometryCollection as an argument

OGC SPEC s2.1.1.1

Envelope(geometry)

Returns a POLYGON representing the bounding box of the geometry.

OGC SPEC s2.1.1.1 - The minimum bounding box for this Geometry, returned as a Geometry. The polygon is defined by the corner points of the bounding box ((MINX, MINY), (MAXX, MINY), (MAXX, MAXY), (MINX, MAXY), (MINX, MINY)).

NOTE:PostGIS will add a Zmin/Zmax coordinate as well.

GeometryType(geometry)

Returns the type of the geometry as a string. Eg: 'LINESTRING', 'POLYGON', 'MULTIPOINT', etc.

OGC SPEC s2.1.1.1 - Returns the name of the instantiable subtype of Geometry of which this Geometry instance is a member. The name of the instantiable subtype of Geometry is returned as a string.

X(geometry)

Find and return the X coordinate of the first point in the geometry. Return NULL if there is no point in the geometry.

Y(geometry)

Find and return the Y coordinate of the first point in the geometry. Return NULL if there is no point in the geometry.

Z(geometry)

Find and return the Z coordinate of the first point in the geometry. Return NULL if there is no point in the geometry.

NumPoints(geometry)

Find and return the number of points in the first linestring in the geometry. Return NULL if there is no linestring in the geometry.

PointN(geometry,integer)

Return the N'th point in the first linestring in the geometry. Return NULL if there is no linestring in the geometry.

ExteriorRing(geometry)

Return the exterior ring of the first polygon in the geometry. Return NULL if there is no polygon in the geometry.

NumInteriorRings(geometry)

Return the number of interior rings of the first polygon in the geometry. Return NULL if there is no polygon in the geometry.

InteriorRingN(geometry,integer)

Return the N'th interior ring of the first polygon in the geometry. Return NULL if there is no polygon in the geometry.

IsClosed(geometry)

Returns true of the geometry start and end points are coincident.

IsRing(geometry)

Returns 1 (TRUE) if this Curve is closed (StartPoint ( ) = EndPoint ( )) and this Curve is simple (does not pass through the same point more than once).

performed by GEOS

OGC spec 2.1.5.1

NumGeometries(geometry)

If geometry is a GEOMETRYCOLLECTION (or MULTI*) return the number of geometries, otherwise return NULL.

GeometryN(geometry,int)

Return the N'th geometry if the geometry is a GEOMETRYCOLLECTION, MULTIPOINT, MULTILINESTRING or MULTIPOLYGON. Otherwise, return NULL.

0 is 1st geometry

Distance(geometry,geometry)

Return the cartesian distance between two geometries in projected units.

AsText(geometry)

Return the Well-Known Text representation of the geometry. For example: POLYGON(0 0,0 1,1 1,1 0,0 0)

OGC SPEC s2.1.1.1

SRID(geometry)

Returns the integer SRID number of the spatial reference system of the geometry.

OGC SPEC s2.1.1.1

GeometryFromText(varchar, integer)

Syntax: GeometryFromText(<geometry>,<SRID>) Convert a Well-Known Text representation of a geometry into a geometry object.

GeomFromText(varchar, integer)

As above. A synonym for GeometryFromText.

SetSRID(geometry)

Set the SRID on a geometry to a particular integer value. Useful in constructing bounding boxes for queries.

EndPoint(geometry)

Returns the last point of the geometry as a point.

StartPoint(geometry)

Returns the first point of the geometry as a point.

Centroid(geometry)

Returns the centroid of the geometry as a point.

Computation will be more accurate if performed by the GEOS module (enabled at compile time).

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