transformations

This module contains functions that compute geometric constructions, or alter geometry size or shape.

ST_BUFFER

ST_BUFFER(geog, radius, units, steps)

Description

Calculates a Geography buffer for input features for a given radius, i.e. the area within the given distance of the input. Units supported are miles, kilometers, and degrees.

Input parameters

geog: GEOGRAPHY input to be buffered.
radius: FLOAT64 distance to draw the buffer (negative values are allowed).
units: STRING|NULL units of length, the supported options are: miles, kilometers, and degrees. If NULLthe default value kilometers is used.
steps: INT64|NULL number of segments used to approximate a quarter circle. If NULL the default value 8 is used.

Return type

GEOGRAPHY

Example

SELECT `carto-un`.carto.ST_BUFFER(
  ST_GEOGPOINT(-74.00, 40.7128),
  1,
  "kilometers",
  10
);
-- POLYGON((-73.9881354374691 40.7127993926494 ...

Additional examples

Bikeshare stations within a San Francisco buffer

ST_CENTERMEAN

ST_CENTERMEAN(geog)

Description

Takes a Feature or FeatureCollection and returns the mean center (average of its vertices).

Input parameters

geog: GEOGRAPHY feature for which to compute the center.

Return type

GEOGRAPHY

Example

SELECT `carto-un`.carto.ST_CENTERMEAN(
  ST_GEOGFROMTEXT("POLYGON ((30 10, 40 40, 20 40, 10 20, 30 10))")
);
-- POINT(25.3890912155939 29.7916831655627)

Additional examples

New police stations based on Chicago crime location clusters

ST_CENTERMEDIAN

ST_CENTERMEDIAN(geog)

Description

Takes a FeatureCollection of points and computes the median center. The median center is understood as the point that requires the least total travel from all other points.

Input parameters

geog: GEOGRAPHY feature for which to compute the center.

Return type

GEOGRAPHY

Example

SELECT `carto-un`.carto.ST_CENTERMEDIAN(
  ST_GEOGFROMTEXT("POLYGON ((30 10, 40 40, 20 40, 10 20, 30 10))")
);
-- POINT(25.3783930513609 29.8376035441371)

ST_CENTEROFMASS

ST_CENTEROFMASS(geog)

Description

Takes any Feature or a FeatureCollection and returns its center of mass (also known as centroid).

Input parameters

geog: GEOGRAPHY feature to be centered.

Return type

GEOGRAPHY

Example

SELECT `carto-un`.carto.ST_CENTEROFMASS(
  ST_GEOGFROMTEXT("POLYGON ((30 10, 40 40, 20 40, 10 20, 30 10))")
);
-- POINT(25.1730977433239 27.2789529273059)

ST_CONCAVEHULL

ST_CONCAVEHULL(geog, maxEdge, units)

Description

Takes a set of points and returns a concave hull Polygon or MultiPolygon. In case that a single or a couple of points are passed as input, the function will return that point or a segment respectively.

Input parameters

geog: ARRAY<GEOGRAPHY> input points.
maxEdge: FLOAT64|NULL the maximum length allowed for an edge of the concave hull. Higher maxEdge values will produce more convex-like hulls. If NULL, the default value infinity is used and it would be equivalent to a Convex Hull.
units: STRING|NULL units of length, the supported options are: miles, kilometers, degrees or radians. If NULLthe default value kilometers is used.

Return type

GEOGRAPHY

Examples

SELECT `carto-un`.carto.ST_CONCAVEHULL(
  [
    ST_GEOGPOINT(-75.833, 39.284),
    ST_GEOGPOINT(-75.6, 39.984),
    ST_GEOGPOINT(-75.221, 39.125),
    ST_GEOGPOINT(-75.521, 39.325)
  ],
  100,
  'kilometers'
);
-- POLYGON((-75.68 39.24425, -75.527 39.2045 ...

SELECT `carto-un-eu`.carto.ST_CONCAVEHULL(
  [
    ST_GEOGPOINT(-75.833, 39.284),
    ST_GEOGPOINT(-75.6, 39.984),
    ST_GEOGPOINT(-75.221, 39.125),
    ST_GEOGPOINT(-75.521, 39.325)
  ],
  100,
  'kilometers'
);
-- POLYGON((-75.68 39.24425, -75.527 39.2045 ...

SELECT carto.ST_CONCAVEHULL(
  [
    ST_GEOGPOINT(-75.833, 39.284),
    ST_GEOGPOINT(-75.6, 39.984),
    ST_GEOGPOINT(-75.221, 39.125),
    ST_GEOGPOINT(-75.521, 39.325)
  ],
  100,
  'kilometers'
);
-- POLYGON((-75.68 39.24425, -75.527 39.2045 ...

SELECT `carto-un`.carto.ST_CONCAVEHULL(
  [
    ST_GEOGPOINT(-75.833, 39.284)
  ],
  100, 'kilometers'
);
-- POINT(-75.833 39.284)

ST_DESTINATION

ST_DESTINATION(startPoint, distance, bearing, units)

Description

Takes a Point and calculates the location of a destination point given a distance in degrees, radians, miles, or kilometers; and a bearing in degrees. This uses the Haversine formula to account for global curvature.

Input parameters

origin: GEOGRAPHY starting point.
distance: FLOAT64 distance from the origin point in the units specified.
bearing: FLOAT64 ranging from -180 to 180 (e.g. 0 is North, 90 is East, 180 is South, -90 is West).
units: STRING|NULL units of length, the supported options are: miles, kilometers, degrees or radians. If NULLthe default value kilometers is used.

Return type

GEOGRAPHY

Example

SELECT `carto-un`.carto.ST_DESTINATION(
  ST_GEOGPOINT(-3.70325,40.4167),
  10,
  45,
  "miles"
);
-- POINT(-3.56862505487045 40.5189626777536)

ST_GREATCIRCLE

ST_GREATCIRCLE(startPoint, endPoint, npoints)

Description

Calculate great circle routes as LineString or MultiLineString. If the start and end points span the antimeridian, the resulting feature will be split into a MultiLineString.

Input parameters

startPoint: GEOGRAPHY source point feature.
endPoint: GEOGRAPHY destination point feature.
npoints: INT64|NULL number of points. If NULL the default value 100 is used.

Return type

GEOGRAPHY

Example

SELECT `carto-un`.carto.ST_GREATCIRCLE(ST_GEOGPOINT(-3.70325,40.4167), ST_GEOGPOINT(-73.9385,40.6643), 20);
-- LINESTRING(-3.70325 40.4167 ...

Additional examples

Computing US airport connections and route interpolations

ST_LINE_INTERPOLATE_POINT

ST_LINE_INTERPOLATE_POINT(geog, distance, units)

Description

Takes a LineString and returns a Point at a specified distance along the line.

Input parameters

geog: GEOGRAPHY input line.
distance: FLOAT64 distance along the line.
units: STRING|NULL units of length, the supported options are: miles, kilometers, degrees and radians. If NULLthe default value kilometers is used.

Return type

GEOGRAPHY

Example

SELECT `carto-un`.carto.ST_LINE_INTERPOLATE_POINT(ST_GEOGFROMTEXT("LINESTRING (-76.091308 18.427501,-76.695556 18.729501,-76.552734 19.40443,-74.61914 19.134789,-73.652343 20.07657,-73.157958 20.210656)"), 250, 'miles');
-- POINT(-74.297592068938 19.4498107103156)

SELECT `carto-un-eu`.carto.ST_LINE_INTERPOLATE_POINT(ST_GEOGFROMTEXT("LINESTRING (-76.091308 18.427501,-76.695556 18.729501,-76.552734 19.40443,-74.61914 19.134789,-73.652343 20.07657,-73.157958 20.210656)"), 250, 'miles');
-- POINT(-74.297592068938 19.4498107103156)

SELECT carto.ST_LINE_INTERPOLATE_POINT(ST_GEOGFROMTEXT("LINESTRING (-76.091308 18.427501,-76.695556 18.729501,-76.552734 19.40443,-74.61914 19.134789,-73.652343 20.07657,-73.157958 20.210656)"), 250, 'miles');
-- POINT(-74.297592068938 19.4498107103156)

Additional examples

Computing US airport connections and route interpolations

ST_POINTONSURFACE

ST_POINTONSURFACE(geog)

Description

Takes any Feature or a FeatureCollection and returns a point that is granted to be inside one of the polygons.

Input parameters

geog: GEOGRAPHY feature to be centered.

Return type

GEOGRAPHY

Example

SELECT `carto-un`.carto.ST_POINTONSURFACE(
  ST_GEOGFROMTEXT("POLYGON ((1.444057 38.791203 ,  1.450457 38.793763 ,  1.457178 38.792403 ,  1.458298 38.781282 ,  1.453418 38.778242 ,  1.445977 38.780482 ,  1.453498 38.781042 ,  1.456218 38.786883 ,  1.450617 38.790643 ,  1.444057 38.791203))")
);
-- POINT(1.456218 38.786883)

SELECT `carto-un-eu`.carto.ST_POINTONSURFACE(
  ST_GEOGFROMTEXT("POLYGON ((1.444057 38.791203 ,  1.450457 38.793763 ,  1.457178 38.792403 ,  1.458298 38.781282 ,  1.453418 38.778242 ,  1.445977 38.780482 ,  1.453498 38.781042 ,  1.456218 38.786883 ,  1.450617 38.790643 ,  1.444057 38.791203))")
);
-- POINT(1.456218 38.786883)

SELECT carto.ST_POINTONSURFACE(
  ST_GEOGFROMTEXT("POLYGON ((1.444057 38.791203 ,  1.450457 38.793763 ,  1.457178 38.792403 ,  1.458298 38.781282 ,  1.453418 38.778242 ,  1.445977 38.780482 ,  1.453498 38.781042 ,  1.456218 38.786883 ,  1.450617 38.790643 ,  1.444057 38.791203))")
);
-- POINT(1.456218 38.786883)

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 960401.

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