jbe@11: pgLatLon v0.3 documentation jbe@11:

pgLatLon v0.3 documentation

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pgLatLon is a spatial database extension for the PostgreSQL object-relational jbe@0: database management system providing geographic data types and spatial indexing jbe@0: for the WGS-84 spheroid.

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While many other spatial databases still use imprecise bounding boxes for many jbe@11: operations, pgLatLon aims to support more precise geometric calculations for jbe@11: all implemented operators. Efficient indexing of geometric objects is provided jbe@2: using space-filling fractal curves. Optimizations on bit level (including jbe@2: logarithmic compression) allow for a highly memory-efficient non-overlapping jbe@2: index suitable for huge datasets.

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pgLatLon is a lightweight solution as it only depends on PostgreSQL itself (and jbe@11: a C compiler for building).

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Unlike competing spatial extensions for PostgreSQL, pgLatLon is available under jbe@0: the permissive MIT/X11 license to avoid problems with viral licenses like the jbe@0: GPLv2/v3.

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Installation

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Automatic installation

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Prerequisites:

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Then simply type:

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make install
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Manual installation

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It is also possible to compile and install the extension without GNU Make as jbe@0: follows:

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cc -Wall -O2 -fPIC -shared -I `pg_config --includedir-server` -o latlon-v0003.so latlon-v0003.c
jbe@13: cp latlon-v0003.so `pg_config --pkglibdir`
jbe@0: cp latlon.control `pg_config --sharedir`/extension/
jbe@13: cp latlon--*.sql `pg_config --sharedir`/extension/
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Loading the extension

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After installation, you can create a database and load the extension as jbe@0: follows:

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% createdb test_database
jbe@0: % psql test_database
jbe@0: psql (9.5.4)
jbe@0: Type "help" for help.
jbe@0: 
jbe@0: test_database=# CREATE EXTENSION latlon;
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Reference

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1. Types

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pgLatLon provides four geographic types: epoint, ebox, ecircle, and jbe@0: ecluster.

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epoint

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A point on the earth spheroid (WGS-84).

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The text input format is '[N|S]<float> [E|W]<float>', where each float is in jbe@0: degrees. Note the required white space between the latitude and longitude jbe@0: components. Each floating point number may have a sign, in which case N/S jbe@0: or E/W are switched respectively (e.g. E-5 is the same as W5).

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An epoint may also be created from two floating point numbers by calling jbe@0: epoint(latitude, longitude), where positive latitudes are used for the jbe@0: northern hemisphere, negative latitudes are used for the southern hemisphere, jbe@0: positive longitudes indicate positions east of the prime meridian, and negative jbe@0: longitudes indicate positions west of the prime meridian.

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Latitudes exceeding -90 or +90 degrees are truncated to -90 or +90 jbe@0: respectively, in which case a warning will be issued. Longitudes exceeding -180 jbe@0: or +180 degrees will be converted to values between -180 and +180 (both jbe@0: inclusive) by adding or substracting a multiple of 360 degrees, in which case a jbe@0: notice will be issued.

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If the latitude is -90 or +90 (south pole or north pole), a longitude value is jbe@0: still stored in the datum, and if a point is on the prime meridian or the jbe@0: 180th meridian, the east/west bit is also stored in the datum. In case of the jbe@0: prime meridian, this is done by storing a floating point value of -0 for jbe@0: 0 degrees west and a value of +0 for 0 degrees east. In case of the jbe@0: 180th meridian, this is done by storing -180 or +180 respectively. The equality jbe@0: operator, however, returns true when the same points on earth are described, jbe@0: i.e. the longitude is ignored for the poles, and 180 degrees west is considered jbe@0: to be equal to 180 degrees east.

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ebox

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An area on earth demarcated by a southern and northern latitude, and a western jbe@0: and eastern longitude (all given in WGS-84).

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The text input format is jbe@0: '{N|S}<float> {E|W}<float> {N|S}<float> {E|W}<float>', where each float is in jbe@0: degrees. The ordering of the four white-space separated blocks is not jbe@0: significant. To include the 180th meridian, one longitude boundary must be jbe@0: equal to or exceed W180 or E180, e.g. 'N10 N20 E170 E190'.

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A special value is the empty area, denoted by the text represenation 'empty'. jbe@0: Such an ebox does not contain any point.

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An ebox may also be created from four floating point numbers by calling jbe@0: ebox(min_latitude, max_latitude, min_longitude, max_longitude), where jbe@0: positive values are used for north and east, and negative values are used for jbe@0: south and west. If min_latitude is strictly greater than max_latitude, an jbe@0: empty ebox is created. If min_longitude is greater than max_longitude and jbe@0: if both longitudes are between -180 and +180 degrees, then the area oriented in jbe@0: such way that the 180th meridian is included.

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If the longitude span is less than 120 degrees, an ebox may be alternatively jbe@0: created from two epoints in the following way: ebox(epoint(lat1, lon1), jbe@0: epoint(lat2, lon2)). In this case lat1 and lat2 as well as lon1 and jbe@0: lon2 can be swapped without any impact.

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ecircle

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An area containing all points not farther away from a given center point jbe@0: (WGS-84) than a given radius.

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The text input format is '{N|S}<float> {E|W}<float> <float>', where the first jbe@0: two floats denote the center point in degrees and the third float denotes the jbe@0: radius in meters. A radius equal to minus infinity denotes an empty circle jbe@0: which contains no point at all (despite having a center), while a radius equal jbe@0: to zero denotes a circle that includes a single point.

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An ecircle may also be created by calling ecircle(epoint(...), radius) or jbe@0: from three floating point numbers by calling ecircle(latitude, longitude, jbe@0: radius).

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ecluster

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A collection of points, paths, polygons, and outlines on the WGS-84 spheroid. jbe@0: Each path, polygon, or outline must cover a longitude range of less than jbe@0: 180 degrees to avoid ambiguities.

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The text input format is a white-space separated list of the following items:

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Paths are open by default (i.e. there is no connection from the last point in jbe@0: the list to the first point in the list). Outlines and polygons, in contrast, jbe@0: are automatically closed (i.e. there is a line segment from the last point in jbe@0: the list to the first point in the list) which means the first point should not jbe@0: be repeated as last point in the list. Polygons are filled, outlines are not.

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2. Indices

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Two kinds of indices are supported: B-tree and GiST indices.

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B-tree indices

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A B-tree index can be used for simple equality searches and is supported by the jbe@0: epoint, ebox, and ecircle data types. B-tree indices can not be used for jbe@0: geographic searches.

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GiST indices

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For geographic searches, GiST indices must be used. The epoint, ecircle, jbe@0: and ecluster data types support GiST indexing. A GiST index for geographic jbe@0: searches can be created as follows:

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CREATE TABLE tbl (
jbe@0:         id              serial4         PRIMARY KEY,
jbe@0:         loc             epoint          NOT NULL );
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jbe@0: CREATE INDEX name_of_index ON tbl USING gist (loc);
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GiST indices also support nearest neighbor searches when using the distance jbe@0: operator (<->) in the ORDER BY clause.

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Indices on other data types (e.g. GeoJSON)

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Note that further types can be indexed by using an index on an expression with jbe@0: a conversion function. One conversion function provided by pgLatLon is the jbe@0: GeoJSON_to_ecluster(float8, float8, text) function:

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CREATE TABLE tbl (
jbe@0:         id              serial4         PRIMARY KEY,
jbe@0:         loc             jsonb           NOT NULL );
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jbe@0: CREATE INDEX name_of_index ON tbl USING gist((GeoJSON_to_ecluster("loc")));
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When using the conversion function in an expression, the index will be used jbe@0: automatically:

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SELECT * FROM tbl WHERE GeoJSON_to_ecluster("loc") && 'N50 E10 10000'::ecircle;
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3. Operators

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Equality operator =

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Tests if two geographic objects are equal.

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The longitude is ignored for the poles, and 180 degrees west is considered to jbe@0: be equal to 180 degrees east.

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For boxes and circles, two empty objects are considered equal. (Note that a jbe@0: circle is not empty if the radius is zero but only if it is negative infinity, jbe@0: i.e. smaller than zero.) Two circles with a positive infinite radius are also jbe@0: considered equal.

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Implemented for:

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The negation is the inequality operator (<> or !=).

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Linear ordering operators <<<, <<<=, >>>=, >>>

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These operators create an arbitrary (but well-defined) linear ordering of jbe@0: geographic objects, which is used internally for B-tree indexing and merge jbe@0: joins. These operators will usually not be used by an application programmer.

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Overlap operator &&

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Tests if two geographic objects have at least one point in common. Currently jbe@0: implemented for:

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The && operator is commutative, i.e. a && b is the same as b && a. Each jbe@0: commutation is supported as well.

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Lossy overlap operator &&+

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Tests if two geographic objects may have at least one point in common. Opposed jbe@11: to the && operator, the &&+ operator may return false positives and is jbe@11: currently implemented for:

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The &&+ operator is commutative, i.e. a &&+ b is the same as b &&+ a. Each jbe@11: commutation is supported as well.

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Where two data types support both the && and the &&+ operator, the &&+ jbe@11: operator computes faster.

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Distance operator <->

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Calculates the shortest distance between two geographic objects in meters (zero jbe@0: if the objects are overlapping). Currently implemented for:

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The <-> operator is commutative, i.e. a <-> b is the same as b <-> a. jbe@0: Each commutation is supported as well.

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For short distances, the result is very accurate (i.e. respects the dimensions jbe@0: of the WGS-84 spheroid). For longer distances in the order of magnitude of jbe@0: earth's radius or greater, the value is only approximate (but the error is jbe@0: still less than 0.2% as long as no polygons with very long edges are involved).

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The functions distance(epoint, epoint) and distance(ecluster, epoint) can jbe@0: be used as an alias for this operator.

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Note: In case of radial searches with a fixed radius, this operator should jbe@0: not be used. Instead, an ecircle should be created and used in combination jbe@0: with the overlap operator (&&). Alternatively, the functions jbe@0: distance_within(epoint, epoint, float8) or distance_within(ecluster, epoint, jbe@0: float8) can be used for fixed-radius searches.

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4. Functions

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center(circle)

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Returns the center of an ecircle as an epoint.

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distance(epoint, epoint)

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Calculates the distance between two epoint datums in meters. This function is jbe@0: an alias for the distance operator <->.

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Note: In case of radial searches with a fixed radius, this function should not be jbe@0: used. Use distance_within(epoint, epoint, float8) instead.

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distance(ecluster, epoint)

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Calculates the distance from an ecluster to an epoint in meters. This jbe@0: function is an alias for the distance operator <->.

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Note: In case of radial searches with a fixed radius, this function should not be jbe@0: used. Use distance_within(epoint, epoint, float8) instead.

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distance_within(variable epoint, fixed epoint, radius float8)

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Checks if the distance between two epoint datums is not greater than a given jbe@0: value (search radius).

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Note: In case of radial searches with a fixed radius, the first argument must jbe@0: be used for the table column, while the second argument must be used for the jbe@0: search center. Otherwise an existing index cannot be used.

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distance_within(variable ecluster, fixed epoint, radius float8)

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Checks if the distance from an ecluster to an epoint is not greater than a jbe@0: given value (search radius).

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ebox(latmin float8, latmax float8, lonmin float8, lonmax float8)

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Creates a new ebox with the given boundaries. jbe@0: See "1. Types", subsection ebox for details.

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ebox(epoint, epoint)

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Creates a new ebox. This function may only be used if the longitude jbe@0: difference is less than or equal to 120 degrees. jbe@0: See "1. Types", subsection ebox for details.

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ecircle(epoint, float8)

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Creates an ecircle with the given center point and radius.

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ecircle(latitude float8, longitude float8, radius float8)

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Creates an ecircle with the given center point and radius.

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ecluster_concat(ecluster, ecluster)

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Combines two clusters to form a new ecluster by uniting all entries of both jbe@0: clusters. Note that two overlapping areas of polygons annihilate each other jbe@0: (which may be used to create polygons with holes).

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ecluster_concat(ecluster[])

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Creates a new ecluster that unites all entries of all clusters in the passed jbe@0: array. Note that two overlapping areas of polygons annihilate each other (which jbe@0: may be used to create polygons with holes).

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ecluster_create_multipoint(epoint[])

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Creates a new ecluster which contains multiple points.

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ecluster_create_outline(epoint[])

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Creates a new ecluster that is an outline given by the passed points.

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ecluster_create_path(epoint[])

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Creates a new ecluster that is a path given by the passed points.

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ecluster_create_polygon(epoint[])

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Creates a new ecluster that is a polygon given by the passed points.

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ecluster_extract_outlines(ecluster)

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Set-returning function that returns the outlines of an ecluster as epoint[] jbe@0: rows.

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ecluster_extract_paths(ecluster)

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Set-returning function that returns the paths of an ecluster as epoint[] jbe@0: rows.

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ecluster_extract_points(ecluster)

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Set-returning function that returns the points of an ecluster as epoint jbe@0: rows.

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ecluster_extract_polygons(ecluster)

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Set-returning function that returns the polygons of an ecluster as epoint[] jbe@0: rows.

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empty_ebox()

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Returns the empty ebox. jbe@0: See "1. Types", subsection ebox for details.

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epoint(latitude float8, longitude float8)

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Returns an epoint with the given latitude and longitude.

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epoint_latlon(latitude float8, longitude float8)

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Alias for epoint(float8, float8).

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epoint_lonlat(longitude float8, latitude float8)

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Same as epoint(float8, float8) but with arguments reversed.

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GeoJSON_to_epoint(jsonb, text)

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Maps a GeoJSON object of type "Point" or "Feature" (which contains a jbe@0: "Point") to an epoint datum. For any other JSON objects, NULL is returned.

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The second parameter (which defaults to epoint_lonlat) may be set to a name jbe@0: of a conversion function that transforms two coordinates (two float8 jbe@0: parameters) to an epoint.

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GeoJSON_to_ecluster(jsonb, text)

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Maps a (valid) GeoJSON object to an ecluster. Note that this function jbe@0: does not check whether the JSONB object is a valid GeoJSON object.

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The second parameter (which defaults to epoint_lonlat) may be set to a name jbe@0: of a conversion function that transforms two coordinates (two float8 jbe@0: parameters) to an epoint.

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max_latitude(ebox)

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Returns the northern boundary of a given ebox in degrees between -90 and +90.

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max_longitude(ebox)

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Returns the eastern boundary of a given ebox in degrees between -180 and +180 jbe@0: (both inclusive).

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min_latitude(ebox)

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Returns the southern boundary of a given ebox in degrees between -90 and +90.

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min_longitude(ebox)

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Returns the western boundary of a given ebox in degrees between -180 and +180 jbe@0: (both inclusive).

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latitude(epoint)

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Returns the latitude value of an epoint in degrees between -90 and +90.

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longitude(epoint)

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Returns the longitude value of an epoint in degrees between -180 and +180 jbe@0: (both inclusive).

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radius(ecircle)

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Returns the radius of an ecircle in meters.

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