Geographic Functions

Geographical functions operate on geographic input, like points, lines or polygons. The built-in general-purpose geographic functions are listed in below.

Geography functions

Function	Description
geo_make_point(latitude double, longitude double) → geography(point)	Creates a point with coordinates latitude and longitude
geo_make_line(a geography(point), b geography(point)) → geography(linestring)	Creates a line between a and b
geo_distance(a geography(point),b geography (point), unit string) → double	Distance in the WGS84 ellipsoid between points a and b expressed in unit
geo_buffer(p geography(point), r double, unit string) → geography(polygon)	120-sided polygon around point p, which is fully enclosed by circle with center in same point and radius r, where radius unit is given in unit. When radius is 0, a single point is returned (the input parameter) instead of a 120-sided polygon
geo_auto_vertex_order(arg geography) → geography	Inverts the vertex order for all polygons if they are specified in an interior-right winding order assuming flat earth to topology 4
geo_invert_vertex_order(arg geography) → geography	Inverts the vertex order of all polygons

note

Explicit use of geo_auto_vertex_order is needed and recommended only when processing extracts generated by Hyper API version v0.0.12514 or earlier. geo_auto_vertex_order is implicitly used when parsing GEOGRAPHY values from WKT format.

Examples

To pass a geography constant as an argument, it needs to be cast from a string which contains a geography object formatted in the Well Known Text (WKT) format defined by the Open GIS Consortium, Inc, in the OpenGIS Simple Features Specification For SQL. More examples of handling geography objects using the Hyper API can be found here. Return values of type geography are also shown in WKT format.

SELECT geo_make_point(20, 30);
Result: point(30.0000003 20.0)
(Note that the latitude and longitude are flipped in the result, because it is shown in the WKT format as point(longitude latitude).)

SELECT geo_make_line('point(14 42)'::geography,'point(18 43)'::geography);
Result: linestring(14.0000003 42.0000002, 18.0000003 43.0000001)

SELECT geo_distance('point(0 0)'::geography, 'point(0 1)'::geography, 'kilometers');
Result: 110.574372592802

SELECT geo_buffer('point(90 45)'::geography, 1989.0, 'meter');
Result: polygon((90.0000002 45.0178973, 89.9986795 45.0178727, ..., 90.0013209 45.0178727, 90.0000002 45.0178973))

SELECT geo_invert_vertex_order('geometrycollection(polygon((0 0, 2 0, 0 4, 0 0)), polygon((0 0, 0 2, 4 0, 0 0)), point(0 2))'::geography);
Result: geometry collection(polygon((0.0 0.0,0.0 4.0,2.0000003 0.0,0.0 0.0)), polygon((0.0 0.0,4.0 0.0,0.0 2.0000003,0.0 0.0)), point(0.0 2.0000003))

SELECT geo_auto_vertex_order('geometrycollection(polygon((0 0, 2 0, 0 4, 0 0)), polygon((0 0, 0 2, 4 0, 0 0)), point(0 2))'::geography);
Result: geometrycollection(polygon((0.0 0.0,2.0000003 0.0,0.0 4.0,0.0 0.0)), polygon((0.0 0.0,4.0 0.0,0.0 2.0000003,0.0 0.0)),point(0.0 2.0000003))

Supported distance units

The supported units of length are:

Unit name in American spelling	Other supported spellings	Description
meter	metre, m, meters, metres	Base unit of length in International System of Units (SI)
kilometer	kilometre, km, kilometers, kilometres	Equal to 1000 meters
mile	mi, miles	Equal to 1609.344 meters
foot	ft, feet	Equal to 0.3048 meters