GoogleSQL for BigQuery supports geography functions.
Geography functions operate on or generate GoogleSQL
GEOGRAPHY
values. The signature of most geography
functions starts with ST_
. GoogleSQL for BigQuery supports the following functions
that can be used to analyze geographical data, determine spatial relationships
between geographical features, and construct or manipulate
GEOGRAPHY
s.
All GoogleSQL geography functions return NULL
if any input argument
is NULL
.
Categories
The geography functions are grouped into the following categories based on their behavior:
Category | Functions | Description |
Constructors |
ST_GEOGPOINT ST_MAKELINE ST_MAKEPOLYGON ST_MAKEPOLYGONORIENTED
|
Functions that build new geography values from coordinates or existing geographies. |
Parsers |
ST_GEOGFROM ST_GEOGFROMGEOJSON ST_GEOGFROMTEXT ST_GEOGFROMWKB ST_GEOGPOINTFROMGEOHASH |
Functions that create geographies from an external format such as WKT and GeoJSON. |
Formatters |
ST_ASBINARY ST_ASGEOJSON ST_ASTEXT ST_GEOHASH
|
Functions that export geographies to an external format such as WKT. |
Transformations |
ST_BOUNDARY ST_BUFFER ST_BUFFERWITHTOLERANCE ST_CENTROID ST_CENTROID_AGG (Aggregate)ST_CLOSESTPOINT ST_CONVEXHULL ST_DIFFERENCE ST_EXTERIORRING ST_INTERIORRINGS ST_INTERSECTION ST_SIMPLIFY ST_SNAPTOGRID ST_UNION ST_UNION_AGG (Aggregate) |
Functions that generate a new geography based on input. |
Accessors |
ST_DIMENSION ST_DUMP ST_ENDPOINT ST_GEOMETRYTYPE ST_ISCLOSED ST_ISCOLLECTION ST_ISEMPTY ST_ISRING ST_NPOINTS ST_NUMGEOMETRIES ST_NUMPOINTS ST_POINTN ST_STARTPOINT ST_X ST_Y |
Functions that provide access to properties of a geography without side-effects. |
Predicates |
ST_CONTAINS ST_COVEREDBY ST_COVERS ST_DISJOINT ST_DWITHIN ST_EQUALS ST_INTERSECTS ST_INTERSECTSBOX ST_TOUCHES ST_WITHIN |
Functions that return TRUE or
FALSE for some spatial
relationship between two
geographies or some property of
a geography. These functions
are commonly used in filter
clauses.
|
Measures |
ST_ANGLE ST_AREA ST_AZIMUTH ST_BOUNDINGBOX ST_DISTANCE ST_EXTENT (Aggregate)ST_LENGTH ST_MAXDISTANCE ST_PERIMETER |
Functions that compute measurements of one or more geographies. |
Clustering |
ST_CLUSTERDBSCAN
|
Functions that perform clustering on geographies. |
S2 functions |
S2_CELLIDFROMPOINT S2_COVERINGCELLIDS |
Functions for working with S2 cell coverings of GEOGRAPHY. |
S2_CELLIDFROMPOINT
S2_CELLIDFROMPOINT(point_geography[, level => cell_level])
Description
Returns the S2 cell ID covering a point GEOGRAPHY
.
- The optional
INT64
parameterlevel
specifies the S2 cell level for the returned cell. Naming this argument is optional.
This is advanced functionality for interoperability with systems utilizing the S2 Geometry Library.
Constraints
- Returns the cell ID as a signed
INT64
bit-equivalent to unsigned 64-bit integer representation. - Can return negative cell IDs.
- Valid S2 cell levels are 0 to 30.
level
defaults to 30 if not explicitly specified.- The function only supports a single point GEOGRAPHY. Use the
SAFE
prefix if the input can be multipoint, linestring, polygon, or an emptyGEOGRAPHY
. - To compute the covering of a complex
GEOGRAPHY
, use S2_COVERINGCELLIDS.
Return type
INT64
Example
WITH data AS (
SELECT 1 AS id, ST_GEOGPOINT(-122, 47) AS geo
UNION ALL
-- empty geography is not supported
SELECT 2 AS id, ST_GEOGFROMTEXT('POINT EMPTY') AS geo
UNION ALL
-- only points are supported
SELECT 3 AS id, ST_GEOGFROMTEXT('LINESTRING(1 2, 3 4)') AS geo
)
SELECT id,
SAFE.S2_CELLIDFROMPOINT(geo) cell30,
SAFE.S2_CELLIDFROMPOINT(geo, level => 10) cell10
FROM data;
+----+---------------------+---------------------+
| id | cell30 | cell10 |
+----+---------------------+---------------------+
| 1 | 6093613931972369317 | 6093613287902019584 |
| 2 | NULL | NULL |
| 3 | NULL | NULL |
+----+---------------------+---------------------+
S2_COVERINGCELLIDS
S2_COVERINGCELLIDS(
geography
[, min_level => cell_level]
[, max_level => cell_level]
[, max_cells => max_cells]
[, buffer => buffer])
Description
Returns an array of S2 cell ids that cover the input
GEOGRAPHY
. The function returns at most max_cells
cells. The optional
arguments min_level
and max_level
specify minimum and maximum levels for
returned S2 cells. The array size is limited by the optional max_cells
argument. The optional buffer
argument specifies a buffering factor in
meters; the region being covered is expanded from the extent of the
input geography by this amount.
This is advanced functionality for interoperability with systems utilizing the S2 Geometry Library.
Constraints
- Returns the cell ID as a signed
INT64
bit-equivalent to unsigned 64-bit integer representation. - Can return negative cell IDs.
- Valid S2 cell levels are 0 to 30.
max_cells
defaults to 8 if not explicitly specified.buffer
should be nonnegative. It defaults to 0.0 meters if not explicitly specified.
Return type
ARRAY<INT64>
Example
WITH data AS (
SELECT 1 AS id, ST_GEOGPOINT(-122, 47) AS geo
UNION ALL
SELECT 2 AS id, ST_GEOGFROMTEXT('POINT EMPTY') AS geo
UNION ALL
SELECT 3 AS id, ST_GEOGFROMTEXT('LINESTRING(-122.12 47.67, -122.19 47.69)') AS geo
)
SELECT id, S2_COVERINGCELLIDS(geo, min_level => 12) cells
FROM data;
+----+--------------------------------------------------------------------------------------+
| id | cells |
+----+--------------------------------------------------------------------------------------+
| 1 | [6093613931972369317] |
| 2 | [] |
| 3 | [6093384954555662336, 6093390709811838976, 6093390735581642752, 6093390740145045504, |
| | 6093390791416217600, 6093390812891054080, 6093390817187069952, 6093496378892222464] |
+----+--------------------------------------------------------------------------------------+
ST_ANGLE
ST_ANGLE(point_geography_1, point_geography_2, point_geography_3)
Description
Takes three point GEOGRAPHY
values, which represent two intersecting lines.
Returns the angle between these lines. Point 2 and point 1 represent the first
line and point 2 and point 3 represent the second line. The angle between
these lines is in radians, in the range [0, 2pi)
. The angle is measured
clockwise from the first line to the second line.
ST_ANGLE
has the following edge cases:
- If points 2 and 3 are the same, returns
NULL
. - If points 2 and 1 are the same, returns
NULL
. - If points 2 and 3 are exactly antipodal, returns
NULL
. - If points 2 and 1 are exactly antipodal, returns
NULL
. - If any of the input geographies are not single points or are the empty geography, then throws an error.
Return type
FLOAT64
Example
WITH geos AS (
SELECT 1 id, ST_GEOGPOINT(1, 0) geo1, ST_GEOGPOINT(0, 0) geo2, ST_GEOGPOINT(0, 1) geo3 UNION ALL
SELECT 2 id, ST_GEOGPOINT(0, 0), ST_GEOGPOINT(1, 0), ST_GEOGPOINT(0, 1) UNION ALL
SELECT 3 id, ST_GEOGPOINT(1, 0), ST_GEOGPOINT(0, 0), ST_GEOGPOINT(1, 0) UNION ALL
SELECT 4 id, ST_GEOGPOINT(1, 0) geo1, ST_GEOGPOINT(0, 0) geo2, ST_GEOGPOINT(0, 0) geo3 UNION ALL
SELECT 5 id, ST_GEOGPOINT(0, 0), ST_GEOGPOINT(-30, 0), ST_GEOGPOINT(150, 0) UNION ALL
SELECT 6 id, ST_GEOGPOINT(0, 0), NULL, NULL UNION ALL
SELECT 7 id, NULL, ST_GEOGPOINT(0, 0), NULL UNION ALL
SELECT 8 id, NULL, NULL, ST_GEOGPOINT(0, 0))
SELECT ST_ANGLE(geo1,geo2,geo3) AS angle FROM geos ORDER BY id;
+---------------------+
| angle |
+---------------------+
| 4.71238898038469 |
| 0.78547432161873854 |
| 0 |
| NULL |
| NULL |
| NULL |
| NULL |
| NULL |
+---------------------+
ST_AREA
ST_AREA(geography_expression[, use_spheroid])
Description
Returns the area in square meters covered by the polygons in the input
GEOGRAPHY
.
If geography_expression
is a point or a line, returns zero. If
geography_expression
is a collection, returns the area of the polygons in the
collection; if the collection does not contain polygons, returns zero.
The optional use_spheroid
parameter determines how this function measures
distance. If use_spheroid
is FALSE
, the function measures distance on the
surface of a perfect sphere.
The use_spheroid
parameter currently only supports
the value FALSE
. The default value of use_spheroid
is FALSE
.
Return type
FLOAT64
ST_ASBINARY
ST_ASBINARY(geography_expression)
Description
Returns the WKB representation of an input
GEOGRAPHY
.
See ST_GEOGFROMWKB
to construct a
GEOGRAPHY
from WKB.
Return type
BYTES
ST_ASGEOJSON
ST_ASGEOJSON(geography_expression)
Description
Returns the RFC 7946 compliant GeoJSON
representation of the input GEOGRAPHY
.
A GoogleSQL GEOGRAPHY
has spherical
geodesic edges, whereas a GeoJSON Geometry
object explicitly has planar edges.
To convert between these two types of edges, GoogleSQL adds additional
points to the line where necessary so that the resulting sequence of edges
remains within 10 meters of the original edge.
See ST_GEOGFROMGEOJSON
to construct a
GEOGRAPHY
from GeoJSON.
Return type
STRING
ST_ASTEXT
ST_ASTEXT(geography_expression)
Description
Returns the WKT representation of an input
GEOGRAPHY
.
See ST_GEOGFROMTEXT
to construct a
GEOGRAPHY
from WKT.
Return type
STRING
ST_AZIMUTH
ST_AZIMUTH(point_geography_1, point_geography_2)
Description
Takes two point GEOGRAPHY
values, and returns the azimuth of the line segment
formed by points 1 and 2. The azimuth is the angle in radians measured between
the line from point 1 facing true North to the line segment from point 1 to
point 2.
The positive angle is measured clockwise on the surface of a sphere. For example, the azimuth for a line segment:
- Pointing North is
0
- Pointing East is
PI/2
- Pointing South is
PI
- Pointing West is
3PI/2
ST_AZIMUTH
has the following edge cases:
- If the two input points are the same, returns
NULL
. - If the two input points are exactly antipodal, returns
NULL
. - If either of the input geographies are not single points or are the empty geography, throws an error.
Return type
FLOAT64
Example
WITH geos AS (
SELECT 1 id, ST_GEOGPOINT(1, 0) AS geo1, ST_GEOGPOINT(0, 0) AS geo2 UNION ALL
SELECT 2, ST_GEOGPOINT(0, 0), ST_GEOGPOINT(1, 0) UNION ALL
SELECT 3, ST_GEOGPOINT(0, 0), ST_GEOGPOINT(0, 1) UNION ALL
-- identical
SELECT 4, ST_GEOGPOINT(0, 0), ST_GEOGPOINT(0, 0) UNION ALL
-- antipode
SELECT 5, ST_GEOGPOINT(-30, 0), ST_GEOGPOINT(150, 0) UNION ALL
-- nulls
SELECT 6, ST_GEOGPOINT(0, 0), NULL UNION ALL
SELECT 7, NULL, ST_GEOGPOINT(0, 0))
SELECT ST_AZIMUTH(geo1, geo2) AS azimuth FROM geos ORDER BY id;
+--------------------+
| azimuth |
+--------------------+
| 4.71238898038469 |
| 1.5707963267948966 |
| 0 |
| NULL |
| NULL |
| NULL |
| NULL |
+--------------------+
ST_BOUNDARY
ST_BOUNDARY(geography_expression)
Description
Returns a single GEOGRAPHY
that contains the union
of the boundaries of each component in the given input
GEOGRAPHY
.
The boundary of each component of a GEOGRAPHY
is
defined as follows:
- The boundary of a point is empty.
- The boundary of a linestring consists of the endpoints of the linestring.
- The boundary of a polygon consists of the linestrings that form the polygon shell and each of the polygon's holes.
Return type
GEOGRAPHY
ST_BOUNDINGBOX
ST_BOUNDINGBOX(geography_expression)
Description
Returns a STRUCT
that represents the bounding box for the specified geography.
The bounding box is the minimal rectangle that encloses the geography. The edges
of the rectangle follow constant lines of longitude and latitude.
Caveats:
- Returns
NULL
if the input isNULL
or an empty geography. - The bounding box might cross the antimeridian if this allows for a smaller
rectangle. In this case, the bounding box has one of its longitudinal bounds
outside of the [-180, 180] range, so that
xmin
is smaller than the eastmost valuexmax
.
Return type
STRUCT<xmin FLOAT64, ymin FLOAT64, xmax FLOAT64, ymax FLOAT64>
.
Bounding box parts:
xmin
: The westmost constant longitude line that bounds the rectangle.xmax
: The eastmost constant longitude line that bounds the rectangle.ymin
: The minimum constant latitude line that bounds the rectangle.ymax
: The maximum constant latitude line that bounds the rectangle.
Example
WITH data AS (
SELECT 1 id, ST_GEOGFROMTEXT('POLYGON((-125 48, -124 46, -117 46, -117 49, -125 48))') g
UNION ALL
SELECT 2 id, ST_GEOGFROMTEXT('POLYGON((172 53, -130 55, -141 70, 172 53))') g
UNION ALL
SELECT 3 id, ST_GEOGFROMTEXT('POINT EMPTY') g
UNION ALL
SELECT 4 id, ST_GEOGFROMTEXT('POLYGON((172 53, -141 70, -130 55, 172 53))', oriented => TRUE)
)
SELECT id, ST_BOUNDINGBOX(g) AS box
FROM data
+----+------------------------------------------+
| id | box |
+----+------------------------------------------+
| 1 | {xmin:-125, ymin:46, xmax:-117, ymax:49} |
| 2 | {xmin:172, ymin:53, xmax:230, ymax:70} |
| 3 | NULL |
| 4 | {xmin:-180, ymin:-90, xmax:180, ymax:90} |
+----+------------------------------------------+
See ST_EXTENT
for the aggregate version of ST_BOUNDINGBOX
.
ST_BUFFER
ST_BUFFER(
geography,
buffer_radius
[, num_seg_quarter_circle => num_segments]
[, use_spheroid => boolean_expression]
[, endcap => endcap_style]
[, side => line_side])
Description
Returns a GEOGRAPHY
that represents the buffer around the input GEOGRAPHY
.
This function is similar to ST_BUFFERWITHTOLERANCE
,
but you specify the number of segments instead of providing tolerance to
determine how much the resulting geography can deviate from the ideal
buffer radius.
geography
: The inputGEOGRAPHY
to encircle with the buffer radius.buffer_radius
:DOUBLE
that represents the radius of the buffer around the input geography. The radius is in meters. Note that polygons contract when buffered with a negativebuffer_radius
. Polygon shells and holes that are contracted to a point are discarded.num_seg_quarter_circle
: (Optional)DOUBLE
specifies the number of segments that are used to approximate a quarter circle. The default value is8.0
. Naming this argument is optional.endcap
: (Optional)STRING
allows you to specify one of two endcap styles:ROUND
andFLAT
. The default value isROUND
. This option only affects the endcaps of buffered linestrings.side
: (Optional)STRING
allows you to specify one of three possibilities for lines:BOTH
,LEFT
, andRIGHT
. The default isBOTH
. This option only affects how linestrings are buffered.use_spheroid
: (Optional)BOOL
determines how this function measures distance. Ifuse_spheroid
isFALSE
, the function measures distance on the surface of a perfect sphere. Theuse_spheroid
parameter currently only supports the valueFALSE
. The default value ofuse_spheroid
isFALSE
.
Return type
Polygon GEOGRAPHY
Example
The following example shows the result of ST_BUFFER
on a point. A buffered
point is an approximated circle. When num_seg_quarter_circle = 2
, there are
two line segments in a quarter circle, and therefore the buffered circle has
eight sides and ST_NUMPOINTS
returns nine vertices. When
num_seg_quarter_circle = 8
, there are eight line segments in a quarter circle,
and therefore the buffered circle has thirty-two sides and
ST_NUMPOINTS
returns thirty-three vertices.
SELECT
-- num_seg_quarter_circle=2
ST_NUMPOINTS(ST_BUFFER(ST_GEOGFROMTEXT('POINT(1 2)'), 50, 2)) AS eight_sides,
-- num_seg_quarter_circle=8, since 8 is the default
ST_NUMPOINTS(ST_BUFFER(ST_GEOGFROMTEXT('POINT(100 2)'), 50)) AS thirty_two_sides;
+-------------+------------------+
| eight_sides | thirty_two_sides |
+-------------+------------------+
| 9 | 33 |
+-------------+------------------+
ST_BUFFERWITHTOLERANCE
ST_BUFFERWITHTOLERANCE(
geography,
buffer_radius,
tolerance_meters => tolernace
[, use_spheroid => boolean_expression]
[, endcap => endcap_style]
[, side => line_side])
Returns a GEOGRAPHY
that represents the buffer around the input GEOGRAPHY
.
This function is similar to ST_BUFFER
,
but you provide tolerance instead of segments to determine how much the
resulting geography can deviate from the ideal buffer radius.
geography
: The inputGEOGRAPHY
to encircle with the buffer radius.buffer_radius
:DOUBLE
that represents the radius of the buffer around the input geography. The radius is in meters. Note that polygons contract when buffered with a negativebuffer_radius
. Polygon shells and holes that are contracted to a point are discarded.tolerance_meters
:DOUBLE
specifies a tolerance in meters with which the shape is approximated. Tolerance determines how much a polygon can deviate from the ideal radius. Naming this argument is optional.endcap
: (Optional)STRING
allows you to specify one of two endcap styles:ROUND
andFLAT
. The default value isROUND
. This option only affects the endcaps of buffered linestrings.side
: (Optional)STRING
allows you to specify one of three possible line styles:BOTH
,LEFT
, andRIGHT
. The default isBOTH
. This option only affects the endcaps of buffered linestrings.use_spheroid
: (Optional)BOOL
determines how this function measures distance. Ifuse_spheroid
isFALSE
, the function measures distance on the surface of a perfect sphere. Theuse_spheroid
parameter currently only supports the valueFALSE
. The default value ofuse_spheroid
isFALSE
.
Return type
Polygon GEOGRAPHY
Example
The following example shows the results of ST_BUFFERWITHTOLERANCE
on a point,
given two different values for tolerance but with the same buffer radius of
100
. A buffered point is an approximated circle. When tolerance_meters=25
,
the tolerance is a large percentage of the buffer radius, and therefore only
five segments are used to approximate a circle around the input point. When
tolerance_meters=1
, the tolerance is a much smaller percentage of the buffer
radius, and therefore twenty-four edges are used to approximate a circle around
the input point.
SELECT
-- tolerance_meters=25, or 25% of the buffer radius.
ST_NumPoints(ST_BUFFERWITHTOLERANCE(ST_GEOGFROMTEXT('POINT(1 2)'), 100, 25)) AS five_sides,
-- tolerance_meters=1, or 1% of the buffer radius.
st_NumPoints(ST_BUFFERWITHTOLERANCE(ST_GEOGFROMTEXT('POINT(100 2)'), 100, 1)) AS twenty_four_sides;
+------------+-------------------+
| five_sides | twenty_four_sides |
+------------+-------------------+
| 6 | 24 |
+------------+-------------------+
ST_CENTROID_AGG
ST_CENTROID_AGG(geography)
Description
Computes the centroid of the set of input GEOGRAPHY
s as a single point
GEOGRAPHY
.
The centroid over the set of input GEOGRAPHY
s is the weighted average of the
centroid of each individual GEOGRAPHY
. Only the GEOGRAPHY
s with the highest
dimension present in the input contribute to the centroid of the entire set.
For example, if the input contains both GEOGRAPHY
s with lines and
GEOGRAPHY
s with only points, ST_CENTROID_AGG
returns the weighted average
of the GEOGRAPHY
s with lines, since those have maximal dimension. In this
example, ST_CENTROID_AGG
ignores GEOGRAPHY
s with only points when
calculating the aggregate centroid.
ST_CENTROID_AGG
ignores NULL
input GEOGRAPHY
values.
See ST_CENTROID
for the non-aggregate version of
ST_CENTROID_AGG
and the definition of centroid for an individual GEOGRAPHY
value.
Return type
Point GEOGRAPHY
Example
The following queries compute the aggregate centroid over a set of
GEOGRAPHY
values. The input to the first query
contains only points, and therefore each value contribute to the aggregate
centroid. Also notice that ST_CENTROID_AGG
is not equivalent to calling
ST_CENTROID
on the result of ST_UNION_AGG
; duplicates are removed by the
union, unlike ST_CENTROID_AGG
. The input to the second query has mixed
dimensions, and only values with the highest dimension in the set, the lines,
affect the aggregate centroid.
SELECT ST_CENTROID_AGG(points) AS st_centroid_agg,
ST_CENTROID(ST_UNION_AGG(points)) AS centroid_of_union
FROM UNNEST([ST_GEOGPOINT(1, 5),
ST_GEOGPOINT(1, 2),
ST_GEOGPOINT(1, -1),
ST_GEOGPOINT(1, -1)]) points;
+---------------------------+-------------------+
| st_centroid_agg | centroid_of_union |
+---------------------------+-------------------+
| POINT(1 1.24961422620969) | POINT(1 2) |
+---------------------------+-------------------+
SELECT ST_CENTROID_AGG(points) AS st_centroid_agg
FROM UNNEST([ST_GEOGPOINT(50, 26),
ST_GEOGPOINT(34, 33.3),
ST_GEOGFROMTEXT('LINESTRING(0 -1, 0 1)'),
ST_GEOGFROMTEXT('LINESTRING(0 1, 0 3)')]) points;
+-----------------+
| st_centroid_agg |
+-----------------+
| POINT(0 1) |
+-----------------+
ST_CENTROID
ST_CENTROID(geography_expression)
Description
Returns the centroid of the input GEOGRAPHY
as a single point GEOGRAPHY
.
The centroid of a GEOGRAPHY
is the weighted average of the centroids of the
highest-dimensional components in the GEOGRAPHY
. The centroid for components
in each dimension is defined as follows:
- The centroid of points is the arithmetic mean of the input coordinates.
- The centroid of linestrings is the centroid of all the edges weighted by length. The centroid of each edge is the geodesic midpoint of the edge.
- The centroid of a polygon is its center of mass.
If the input GEOGRAPHY
is empty, an empty GEOGRAPHY
is returned.
Constraints
In the unlikely event that the centroid of a GEOGRAPHY
cannot be defined by a
single point on the surface of the Earth, a deterministic but otherwise
arbitrary point is returned. This can only happen if the centroid is exactly at
the center of the Earth, such as the centroid for a pair of antipodal points,
and the likelihood of this happening is vanishingly small.
Return type
Point GEOGRAPHY
ST_CLOSESTPOINT
ST_CLOSESTPOINT(geography_1, geography_2[, use_spheroid])
Description
Returns a GEOGRAPHY
containing a point on
geography_1
with the smallest possible distance to geography_2
. This implies
that the distance between the point returned by ST_CLOSESTPOINT
and
geography_2
is less than or equal to the distance between any other point on
geography_1
and geography_2
.
If either of the input GEOGRAPHY
s is empty, ST_CLOSESTPOINT
returns NULL
.
The optional use_spheroid
parameter determines how this function measures
distance. If use_spheroid
is FALSE
, the function measures distance on the
surface of a perfect sphere.
The use_spheroid
parameter currently only supports
the value FALSE
. The default value of use_spheroid
is FALSE
.
Return type
Point GEOGRAPHY
ST_CLUSTERDBSCAN
ST_CLUSTERDBSCAN(geography_column, epsilon, minimum_geographies)
OVER over_clause
over_clause:
{ named_window | ( [ window_specification ] ) }
window_specification:
[ named_window ]
[ PARTITION BY partition_expression [, ...] ]
[ ORDER BY expression [ { ASC | DESC } ] [, ...] ]
Performs DBSCAN clustering on a column of geographies. Returns a 0-based cluster number.
To learn more about the OVER
clause and how to use it, see
Window function calls.
Input parameters
geography_column
: A column ofGEOGRAPHY
s that is clustered.epsilon
: The epsilon that specifies the radius, measured in meters, around a core value. Non-negativeFLOAT64
value.minimum_geographies
: Specifies the minimum number of geographies in a single cluster. Only dense input forms a cluster, otherwise it is classified as noise. Non-negativeINT64
value.
Geography types and the DBSCAN algorithm
The DBSCAN algorithm identifies high-density clusters of data and marks outliers
in low-density areas of noise. Geographies passed in through geography_column
are classified in one of three ways by the DBSCAN algorithm:
- Core value: A geography is a core value if it is within
epsilon
distance ofminimum_geographies
geographies, including itself. The core value starts a new cluster, or is added to the same cluster as a core value withinepsilon
distance. Core values are grouped in a cluster together with all other core and border values that are withinepsilon
distance. - Border value: A geography is a border value if it is within epsilon distance
of a core value. It is added to the same cluster as a core value within
epsilon
distance. A border value may be withinepsilon
distance of more than one cluster. In this case, it may be arbitrarily assigned to either cluster and the function will produce the same result in subsequent calls. - Noise: A geography is noise if it is neither a core nor a border value.
Noise values are assigned to a
NULL
cluster. An emptyGEOGRAPHY
is always classified as noise.
Constraints
- The argument
minimum_geographies
is a non-negativeINT64
andepsilon
is a non-negativeFLOAT64
. - An empty geography cannot join any cluster.
- Multiple clustering assignments could be possible for a border value. If a
geography is a border value,
ST_CLUSTERDBSCAN
will assign it to an arbitrary valid cluster.
Return type
INT64
for each geography in the geography column.
Examples
This example performs DBSCAN clustering with a radius of 100,000 meters with a
minimum_geographies
argument of 1. The geographies being analyzed are a
mixture of points, lines, and polygons.
WITH Geos as
(SELECT 1 as row_id, ST_GEOGFROMTEXT('POINT EMPTY') as geo UNION ALL
SELECT 2, ST_GEOGFROMTEXT('MULTIPOINT(1 1, 2 2, 4 4, 5 2)') UNION ALL
SELECT 3, ST_GEOGFROMTEXT('POINT(14 15)') UNION ALL
SELECT 4, ST_GEOGFROMTEXT('LINESTRING(40 1, 42 34, 44 39)') UNION ALL
SELECT 5, ST_GEOGFROMTEXT('POLYGON((40 2, 40 1, 41 2, 40 2))'))
SELECT row_id, geo, ST_CLUSTERDBSCAN(geo, 1e5, 1) OVER () AS cluster_num FROM
Geos ORDER BY row_id
+--------+-----------------------------------+-------------+
| row_id | geo | cluster_num |
+--------+-----------------------------------+-------------+
|1 | GEOMETRYCOLLECTION EMPTY |NULL |
|2 | MULTIPOINT(1 1, 2 2, 5 2, 4 4) |0 |
|3 | POINT(14 15) |1 |
|4 | LINESTRING(40 1, 42 34, 44 39) |2 |
|5 | POLYGON((40 2, 40 1, 41 2, 40 2)) |2 |
+--------+-----------------------------------+-------------+
ST_CONTAINS
ST_CONTAINS(geography_1, geography_2)
Description
Returns TRUE
if no point of geography_2
is outside geography_1
, and
the interiors intersect; returns FALSE
otherwise.
NOTE: A GEOGRAPHY
does not contain its own
boundary. Compare with ST_COVERS
.
Return type
BOOL
Example
The following query tests whether the polygon POLYGON((1 1, 20 1, 10 20, 1 1))
contains each of the three points (0, 0)
, (1, 1)
, and (10, 10)
, which lie
on the exterior, the boundary, and the interior of the polygon respectively.
SELECT
ST_GEOGPOINT(i, i) AS p,
ST_CONTAINS(ST_GEOGFROMTEXT('POLYGON((1 1, 20 1, 10 20, 1 1))'),
ST_GEOGPOINT(i, i)) AS `contains`
FROM UNNEST([0, 1, 10]) AS i;
+--------------+----------+
| p | contains |
+--------------+----------+
| POINT(0 0) | FALSE |
| POINT(1 1) | FALSE |
| POINT(10 10) | TRUE |
+--------------+----------+
ST_CONVEXHULL
ST_CONVEXHULL(geography_expression)
Description
Returns the convex hull for the input GEOGRAPHY
. The convex hull is the
smallest convex GEOGRAPHY
that covers the input. A GEOGRAPHY
is convex if
for every pair of points in the GEOGRAPHY
, the geodesic edge connecting the
points are also contained in the same GEOGRAPHY
.
In most cases, the convex hull consists of a single polygon. Notable edge cases include the following:
- The convex hull of a single point is also a point.
- The convex hull of two or more collinear points is a linestring as long as that linestring is convex.
- If the input
GEOGRAPHY
spans more than a hemisphere, the convex hull is the full globe. This includes any input that contains a pair of antipodal points. ST_CONVEXHULL
returnsNULL
if the input is eitherNULL
or the emptyGEOGRAPHY
.
Return type
GEOGRAPHY
Examples
The convex hull returned by ST_CONVEXHULL
can be a point, linestring, or a
polygon, depending on the input.
WITH Geographies AS
(SELECT ST_GEOGFROMTEXT('POINT(1 1)') AS g UNION ALL
SELECT ST_GEOGFROMTEXT('LINESTRING(1 1, 2 2)') AS g UNION ALL
SELECT ST_GEOGFROMTEXT('MULTIPOINT(2 11, 4 12, 0 15, 1 9, 1 12)') AS g)
SELECT
g AS input_geography,
ST_CONVEXHULL(g) AS convex_hull
FROM Geographies;
+-----------------------------------------+--------------------------------------------------------+
| input_geography | convex_hull |
+-----------------------------------------+--------------------------------------------------------+
| POINT(1 1) | POINT(0.999999999999943 1) |
| LINESTRING(1 1, 2 2) | LINESTRING(2 2, 1.49988573656168 1.5000570914792, 1 1) |
| MULTIPOINT(1 9, 4 12, 2 11, 1 12, 0 15) | POLYGON((1 9, 4 12, 0 15, 1 9)) |
+-----------------------------------------+--------------------------------------------------------+
ST_COVEREDBY
ST_COVEREDBY(geography_1, geography_2)
Description
Returns FALSE
if geography_1
or geography_2
is empty. Returns TRUE
if no
points of geography_1
lie in the exterior of geography_2
.
Given two GEOGRAPHY
s a
and b
,
ST_COVEREDBY(a, b)
returns the same result as
ST_COVERS
(b, a)
. Note the opposite order of arguments.
Return type
BOOL
ST_COVERS
ST_COVERS(geography_1, geography_2)
Description
Returns FALSE
if geography_1
or geography_2
is empty.
Returns TRUE
if no points of geography_2
lie in the exterior of
geography_1
.
Return type
BOOL
Example
The following query tests whether the polygon POLYGON((1 1, 20 1, 10 20, 1 1))
covers each of the three points (0, 0)
, (1, 1)
, and (10, 10)
, which lie
on the exterior, the boundary, and the interior of the polygon respectively.
SELECT
ST_GEOGPOINT(i, i) AS p,
ST_COVERS(ST_GEOGFROMTEXT('POLYGON((1 1, 20 1, 10 20, 1 1))'),
ST_GEOGPOINT(i, i)) AS `covers`
FROM UNNEST([0, 1, 10]) AS i;
+--------------+--------+
| p | covers |
+--------------+--------+
| POINT(0 0) | FALSE |
| POINT(1 1) | TRUE |
| POINT(10 10) | TRUE |
+--------------+--------+
ST_DIFFERENCE
ST_DIFFERENCE(geography_1, geography_2)
Description
Returns a GEOGRAPHY
that represents the point set
difference of geography_1
and geography_2
. Therefore, the result consists of
the part of geography_1
that does not intersect with geography_2
.
If geometry_1
is completely contained in geometry_2
, then ST_DIFFERENCE
returns an empty GEOGRAPHY
.
Constraints
The underlying geometric objects that a GoogleSQL
GEOGRAPHY
represents correspond to a closed point
set. Therefore, ST_DIFFERENCE
is the closure of the point set difference of
geography_1
and geography_2
. This implies that if geography_1
and
geography_2
intersect, then a portion of the boundary of geography_2
could
be in the difference.
Return type
GEOGRAPHY
Example
The following query illustrates the difference between geog1
, a larger polygon
POLYGON((0 0, 10 0, 10 10, 0 0))
and geog1
, a smaller polygon
POLYGON((4 2, 6 2, 8 6, 4 2))
that intersects with geog1
. The result is
geog1
with a hole where geog2
intersects with it.
SELECT
ST_DIFFERENCE(
ST_GEOGFROMTEXT('POLYGON((0 0, 10 0, 10 10, 0 0))'),
ST_GEOGFROMTEXT('POLYGON((4 2, 6 2, 8 6, 4 2))')
);
+--------------------------------------------------------+
| difference_of_geog1_and_geog2 |
+--------------------------------------------------------+
| POLYGON((0 0, 10 0, 10 10, 0 0), (8 6, 6 2, 4 2, 8 6)) |
+--------------------------------------------------------+
ST_DIMENSION
ST_DIMENSION(geography_expression)
Description
Returns the dimension of the highest-dimensional element in the input
GEOGRAPHY
.
The dimension of each possible element is as follows:
- The dimension of a point is
0
. - The dimension of a linestring is
1
. - The dimension of a polygon is
2
.
If the input GEOGRAPHY
is empty, ST_DIMENSION
returns -1
.
Return type
INT64
ST_DISJOINT
ST_DISJOINT(geography_1, geography_2)
Description
Returns TRUE
if the intersection of geography_1
and geography_2
is empty,
that is, no point in geography_1
also appears in geography_2
.
ST_DISJOINT
is the logical negation of ST_INTERSECTS
.
Return type
BOOL
ST_DISTANCE
ST_DISTANCE(geography_1, geography_2[, use_spheroid])
Description
Returns the shortest distance in meters between two non-empty
GEOGRAPHY
s.
If either of the input GEOGRAPHY
s is empty,
ST_DISTANCE
returns NULL
.
The optional use_spheroid
parameter determines how this function measures
distance. If use_spheroid
is FALSE
, the function measures distance on the
surface of a perfect sphere. If use_spheroid
is TRUE
, the function measures
distance on the surface of the WGS84 spheroid. The default value
of use_spheroid
is FALSE
.
Return type
FLOAT64
ST_DUMP
ST_DUMP(geography[, dimension])
Description
Returns an ARRAY
of simple
GEOGRAPHY
s where each element is a component of
the input GEOGRAPHY
. A simple
GEOGRAPHY
consists of a single point, linestring,
or polygon. If the input GEOGRAPHY
is simple, the
result is a single element. When the input
GEOGRAPHY
is a collection, ST_DUMP
returns an
ARRAY
with one simple
GEOGRAPHY
for each component in the collection.
If dimension
is provided, the function only returns
GEOGRAPHY
s of the corresponding dimension. A
dimension of -1 is equivalent to omitting dimension
.
Return Type
ARRAY<GEOGRAPHY>
Examples
The following example shows how ST_DUMP
returns the simple geographies within
a complex geography.
WITH example AS (
SELECT ST_GEOGFROMTEXT('POINT(0 0)') AS geography
UNION ALL
SELECT ST_GEOGFROMTEXT('MULTIPOINT(0 0, 1 1)') AS geography
UNION ALL
SELECT ST_GEOGFROMTEXT('GEOMETRYCOLLECTION(POINT(0 0), LINESTRING(1 2, 2 1))'))
SELECT
geography AS original_geography,
ST_DUMP(geography) AS dumped_geographies
FROM example
+-------------------------------------+------------------------------------+
| original_geographies | dumped_geographies |
+-------------------------------------+------------------------------------+
| POINT(0 0) | [POINT(0 0)] |
| MULTIPOINT(0 0, 1 1) | [POINT(0 0), POINT(1 1)] |
| GEOMETRYCOLLECTION(POINT(0 0), | [POINT(0 0), LINESTRING(1 2, 2 1)] |
| LINESTRING(1 2, 2 1)) | |
+-------------------------------------+------------------------------------+
The following example shows how ST_DUMP
with the dimension argument only
returns simple geographies of the given dimension.
WITH example AS (
SELECT ST_GEOGFROMTEXT('GEOMETRYCOLLECTION(POINT(0 0), LINESTRING(1 2, 2 1))') AS geography)
SELECT
geography AS original_geography,
ST_DUMP(geography, 1) AS dumped_geographies
FROM example
+-------------------------------------+------------------------------+
| original_geographies | dumped_geographies |
+-------------------------------------+------------------------------+
| GEOMETRYCOLLECTION(POINT(0 0), | [LINESTRING(1 2, 2 1)] |
| LINESTRING(1 2, 2 1)) | |
+-------------------------------------+------------------------------+
ST_DWITHIN
ST_DWITHIN(geography_1, geography_2, distance[, use_spheroid])
Description
Returns TRUE
if the distance between at least one point in geography_1
and
one point in geography_2
is less than or equal to the distance given by the
distance
argument; otherwise, returns FALSE
. If either input
GEOGRAPHY
is empty, ST_DWithin
returns FALSE
. The
given distance
is in meters on the surface of the Earth.
The optional use_spheroid
parameter determines how this function measures
distance. If use_spheroid
is FALSE
, the function measures distance on the
surface of a perfect sphere.
The use_spheroid
parameter currently only supports
the value FALSE
. The default value of use_spheroid
is FALSE
.
Return type
BOOL
ST_ENDPOINT
ST_ENDPOINT(linestring_geography)
Description
Returns the last point of a linestring geography as a point geography. Returns
an error if the input is not a linestring or if the input is empty. Use the
SAFE
prefix to obtain NULL
for invalid input instead of an error.
Return Type
Point GEOGRAPHY
Example
SELECT ST_ENDPOINT(ST_GEOGFROMTEXT('LINESTRING(1 1, 2 1, 3 2, 3 3)')) last
+--------------+
| last |
+--------------+
| POINT(3 3) |
+--------------+
ST_EQUALS
ST_EQUALS(geography_1, geography_2)
Description
Returns TRUE
if geography_1
and geography_2
represent the same
GEOGRAPHY
value. More precisely, this means that
one of the following conditions holds:
+ ST_COVERS(geography_1, geography_2) = TRUE
and ST_COVERS(geography_2,
geography_1) = TRUE
+ Both geography_1
and geography_2
are empty.
Therefore, two GEOGRAPHY
s may be equal even if the
ordering of points or vertices differ, as long as they still represent the same
geometric structure.
Constraints
ST_EQUALS
is not guaranteed to be a transitive function.
Return type
BOOL
ST_EXTENT
ST_EXTENT(geography_expression)
Description
Returns a STRUCT
that represents the bounding box for the set of input
GEOGRAPHY
values. The bounding box is the minimal rectangle that encloses the
geography. The edges of the rectangle follow constant lines of longitude and
latitude.
Caveats:
- Returns
NULL
if all the inputs areNULL
or empty geographies. - The bounding box might cross the antimeridian if this allows for a smaller
rectangle. In this case, the bounding box has one of its longitudinal bounds
outside of the [-180, 180] range, so that
xmin
is smaller than the eastmost valuexmax
. - If the longitude span of the bounding box is larger than or equal to 180 degrees, the function returns the bounding box with the longitude range of [-180, 180].
Return type
STRUCT<xmin FLOAT64, ymin FLOAT64, xmax FLOAT64, ymax FLOAT64>
.
Bounding box parts:
xmin
: The westmost constant longitude line that bounds the rectangle.xmax
: The eastmost constant longitude line that bounds the rectangle.ymin
: The minimum constant latitude line that bounds the rectangle.ymax
: The maximum constant latitude line that bounds the rectangle.
Example
WITH data AS (
SELECT 1 id, ST_GEOGFROMTEXT('POLYGON((-125 48, -124 46, -117 46, -117 49, -125 48))') g
UNION ALL
SELECT 2 id, ST_GEOGFROMTEXT('POLYGON((172 53, -130 55, -141 70, 172 53))') g
UNION ALL
SELECT 3 id, ST_GEOGFROMTEXT('POINT EMPTY') g
)
SELECT ST_EXTENT(g) AS box
FROM data
+----------------------------------------------+
| box |
+----------------------------------------------+
| {xmin:172, ymin:46, xmax:243, ymax:70} |
+----------------------------------------------+
ST_BOUNDINGBOX
for the non-aggregate version of ST_EXTENT
.
ST_EXTERIORRING
ST_EXTERIORRING(polygon_geography)
Description
Returns a linestring geography that corresponds to the outermost ring of a polygon geography.
- If the input geography is a polygon, gets the outermost ring of the polygon geography and returns the corresponding linestring.
- If the input is the full
GEOGRAPHY
, returns an empty geography. - Returns an error if the input is not a single polygon.
Use the SAFE
prefix to return NULL
for invalid input instead of an error.
Return type
- Linestring
GEOGRAPHY
- Empty
GEOGRAPHY
Examples
WITH geo as
(SELECT ST_GEOGFROMTEXT('POLYGON((0 0, 1 4, 2 2, 0 0))') AS g UNION ALL
SELECT ST_GEOGFROMTEXT('''POLYGON((1 1, 1 10, 5 10, 5 1, 1 1),
(2 2, 3 4, 2 4, 2 2))''') as g)
SELECT ST_EXTERIORRING(g) AS ring FROM geo;
+---------------------------------------+
| ring |
+---------------------------------------+
| LINESTRING(2 2, 1 4, 0 0, 2 2) |
| LINESTRING(5 1, 5 10, 1 10, 1 1, 5 1) |
+---------------------------------------+
ST_GEOGFROM
ST_GEOGFROM(expression)
Description
Converts an expression for a STRING
or BYTES
value into a
GEOGRAPHY
value.
If expression
represents a STRING
value, it must be a valid
GEOGRAPHY
representation in one of the following formats:
- WKT format. To learn more about this format and the requirements to use it, see ST_GEOGFROMTEXT.
- WKB in hexadecimal text format. To learn more about this format and the requirements to use it, see ST_GEOGFROMWKB.
- GeoJSON format. To learn more about this format and the requirements to use it, see ST_GEOGFROMGEOJSON.
If expression
represents a BYTES
value, it must be a valid GEOGRAPHY
binary expression in WKB format. To learn more about this format and the
requirements to use it, see ST_GEOGFROMWKB.
If expression
is NULL
, the output is NULL
.
Return type
GEOGRAPHY
Examples
This takes a WKT-formatted string and returns a GEOGRAPHY
polygon:
SELECT ST_GEOGFROM('POLYGON((0 0, 0 2, 2 2, 2 0, 0 0))') AS WKT_format
+------------------------------------+
| WKT_format |
+------------------------------------+
| POLYGON((2 0, 2 2, 0 2, 0 0, 2 0)) |
+------------------------------------+
This takes a WKB-formatted hexadecimal-encoded string and returns a
GEOGRAPHY
point:
SELECT ST_GEOGFROM(FROM_HEX('010100000000000000000000400000000000001040')) AS WKB_format
+----------------+
| WKB_format |
+----------------+
| POINT(2 4) |
+----------------+
This takes WKB-formatted bytes and returns a GEOGRAPHY
point:
SELECT ST_GEOGFROM('010100000000000000000000400000000000001040')-AS WKB_format
+----------------+
| WKB_format |
+----------------+
| POINT(2 4) |
+----------------+
This takes a GeoJSON-formatted string and returns a GEOGRAPHY
polygon:
SELECT ST_GEOGFROM(
'{ "type": "Polygon", "coordinates": [ [ [2, 0], [2, 2], [1, 2], [0, 2], [0, 0], [2, 0] ] ] }'
) AS GEOJSON_format
+-----------------------------------------+
| GEOJSON_format |
+-----------------------------------------+
| POLYGON((2 0, 2 2, 1 2, 0 2, 0 0, 2 0)) |
+-----------------------------------------+
ST_GEOGFROMGEOJSON
ST_GEOGFROMGEOJSON(geojson_string [, make_valid => constant_expression])
Description
Returns a GEOGRAPHY
value that corresponds to the
input GeoJSON representation.
ST_GEOGFROMGEOJSON
accepts input that is RFC 7946
compliant.
If the parameter make_valid
is set to TRUE
, the function attempts to repair
polygons that don't conform to Open Geospatial Consortium semantics.
This parameter uses named argument syntax, and should be specified using
make_valid => argument_value
syntax.
A GoogleSQL GEOGRAPHY
has spherical
geodesic edges, whereas a GeoJSON Geometry
object explicitly has planar edges.
To convert between these two types of edges, GoogleSQL adds additional
points to the line where necessary so that the resulting sequence of edges
remains within 10 meters of the original edge.
See ST_ASGEOJSON
to format a
GEOGRAPHY
as GeoJSON.
Constraints
The JSON input is subject to the following constraints:
ST_GEOGFROMGEOJSON
only accepts JSON geometry fragments and cannot be used to ingest a whole JSON document.- The input JSON fragment must consist of a GeoJSON geometry type, which
includes
Point
,MultiPoint
,LineString
,MultiLineString
,Polygon
,MultiPolygon
, andGeometryCollection
. Any other GeoJSON type such asFeature
orFeatureCollection
will result in an error. - A position in the
coordinates
member of a GeoJSON geometry type must consist of exactly two elements. The first is the longitude and the second is the latitude. Therefore,ST_GEOGFROMGEOJSON
does not support the optional third element for a position in thecoordinates
member.
Return type
GEOGRAPHY
ST_GEOGFROMTEXT
Signature 1
ST_GEOGFROMTEXT(wkt_string[, oriented])
Description
Returns a GEOGRAPHY
value that corresponds to the
input WKT representation.
This function supports an optional parameter of type
BOOL
, oriented
. If this parameter is set to
TRUE
, any polygons in the input are assumed to be oriented as follows:
if someone walks along the boundary of the polygon in the order of
the input vertices, the interior of the polygon is on the left. This allows
WKT to represent polygons larger than a hemisphere. If oriented
is FALSE
or
omitted, this function returns the polygon with the smaller area.
See also ST_MAKEPOLYGONORIENTED
which is similar
to ST_GEOGFROMTEXT
with oriented=TRUE
.
To format GEOGRAPHY
as WKT, use
ST_ASTEXT
.
Constraints
- All input edges are assumed to be spherical geodesics, and not planar
straight lines. For reading data in a planar projection, consider using
ST_GEOGFROMGEOJSON
. For more information on the differences between spherical geodesics and planar lines, see Coordinate systems and edges. - The function does not support three-dimensional geometries that have a
Z
suffix, nor does it support linear referencing system geometries with anM
suffix. - The function only supports geometry primitives and multipart geometries. In particular it supports only point, multipoint, linestring, multilinestring, polygon, multipolygon, and geometry collection.
Return type
GEOGRAPHY
Example
The following query reads the WKT string POLYGON((0 0, 0 2, 2 2, 2 0, 0 0))
both as a non-oriented polygon and as an oriented polygon, and checks whether
each result contains the point (1, 1)
.
WITH polygon AS (SELECT 'POLYGON((0 0, 0 2, 2 2, 2 0, 0 0))' AS p)
SELECT
ST_CONTAINS(ST_GEOGFROMTEXT(p), ST_GEOGPOINT(1, 1)) AS fromtext_default,
ST_CONTAINS(ST_GEOGFROMTEXT(p, FALSE), ST_GEOGPOINT(1, 1)) AS non_oriented,
ST_CONTAINS(ST_GEOGFROMTEXT(p, TRUE), ST_GEOGPOINT(1, 1)) AS oriented
FROM polygon;
+-------------------+---------------+-----------+
| fromtext_default | non_oriented | oriented |
+-------------------+---------------+-----------+
| TRUE | TRUE | FALSE |
+-------------------+---------------+-----------+
Signature 2
ST_GEOGFROMTEXT(wkt_string[, oriented => boolean_constant_1]
[, planar => boolean_constant_2] [, make_valid => boolean_constant_3])
Description
Returns a GEOGRAPHY
value that corresponds to the
input WKT representation.
This function supports three optional parameters of type
BOOL
: oriented
, planar
, and make_valid
.
This signature uses named arguments syntax, and the parameters should be
specified using parameter_name => parameter_value
syntax, in any order.
If the oriented
parameter is set to
TRUE
, any polygons in the input are assumed to be oriented as follows:
if someone walks along the boundary of the polygon in the order of
the input vertices, the interior of the polygon is on the left. This allows
WKT to represent polygons larger than a hemisphere. If oriented
is FALSE
or
omitted, this function returns the polygon with the smaller area.
See also ST_MAKEPOLYGONORIENTED
which is similar
to ST_GEOGFROMTEXT
with oriented=TRUE
.
If the parameter planar
is set to TRUE
, the edges of the line strings and
polygons are assumed to use planar map semantics, rather than GoogleSQL
default spherical geodesics semantics. For more information
on the differences between spherical geodesics and planar lines, see
Coordinate systems and edges.
If the parameter make_valid
is set to TRUE
, the function attempts to repair
polygons that don't conform to Open Geospatial Consortium semantics.
To format GEOGRAPHY
as WKT, use
ST_ASTEXT
.
Constraints
- All input edges are assumed to be spherical geodesics by default, and not
planar straight lines. For reading data in a planar projection,
pass
planar => TRUE
argument, or consider usingST_GEOGFROMGEOJSON
. For more information on the differences between spherical geodesics and planar lines, see Coordinate systems and edges. - The function does not support three-dimensional geometries that have a
Z
suffix, nor does it support linear referencing system geometries with anM
suffix. - The function only supports geometry primitives and multipart geometries. In particular it supports only point, multipoint, linestring, multilinestring, polygon, multipolygon, and geometry collection.
oriented
andplanar
cannot be equal toTRUE
at the same time.oriented
andmake_valid
cannot be equal toTRUE
at the same time.
Example
The following query reads the WKT string POLYGON((0 0, 0 2, 2 2, 0 2, 0 0))
both as a non-oriented polygon and as an oriented polygon, and checks whether
each result contains the point (1, 1)
.
WITH polygon AS (SELECT 'POLYGON((0 0, 0 2, 2 2, 2 0, 0 0))' AS p)
SELECT
ST_CONTAINS(ST_GEOGFROMTEXT(p), ST_GEOGPOINT(1, 1)) AS fromtext_default,
ST_CONTAINS(ST_GEOGFROMTEXT(p, oriented => FALSE), ST_GEOGPOINT(1, 1)) AS non_oriented,
ST_CONTAINS(ST_GEOGFROMTEXT(p, oriented => TRUE), ST_GEOGPOINT(1, 1)) AS oriented
FROM polygon;
+-------------------+---------------+-----------+
| fromtext_default | non_oriented | oriented |
+-------------------+---------------+-----------+
| TRUE | TRUE | FALSE |
+-------------------+---------------+-----------+
The following query converts a WKT string with an invalid polygon to
GEOGRAPHY
. The WKT string violates two properties
of a valid polygon - the loop describing the polygon is not closed, and it
contains self-intersection. With the make_valid
option, ST_GEOGFROMTEXT
successfully converts it to a multipolygon shape.
WITH data AS (
SELECT 'POLYGON((0 -1, 2 1, 2 -1, 0 1))' wkt)
SELECT
SAFE.ST_GEOGFROMTEXT(wkt) as geom,
SAFE.ST_GEOGFROMTEXT(wkt, make_valid => TRUE) as valid_geom
FROM data
+------+-----------------------------------------------------------------+
| geom | valid_geom |
+------+-----------------------------------------------------------------+
| NULL | MULTIPOLYGON(((0 -1, 1 0, 0 1, 0 -1)), ((1 0, 2 -1, 2 1, 1 0))) |
+------+-----------------------------------------------------------------+
ST_GEOGFROMWKB
ST_GEOGFROMWKB(wkb_bytes_expression)
ST_GEOGFROMWKB(wkb_hex_string_expression)
Description
Converts an expression for a hexadecimal-text STRING
or BYTES
value into a GEOGRAPHY
value. The expression must be in
WKB format.
To format GEOGRAPHY
as WKB, use
ST_ASBINARY
.
Constraints
All input edges are assumed to be spherical geodesics, and not planar straight
lines. For reading data in a planar projection, consider using
ST_GEOGFROMGEOJSON
.
Return type
GEOGRAPHY
ST_GEOGPOINT