Geospatial Capabilities

HEAVY.AI supports a subset of object types and functions for storing and writing queries for geospatial definitions.

Geospatial Datatypes

Type

Size

Example

LINESTRING

Variable

A sequence of 2 or more points and the lines that connect them. For example: LINESTRING(0 0,1 1,1 2)

MULTIPOLYGON

Variable

A set of one or more polygons. For example:MULTIPOLYGON(((0 0,4 0,4 4,0 4,0 0),(1 1,2 1,2 2,1 2,1 1)), ((-1 -1,-1 -2,-2 -2,-2 -1,-1 -1)))

POINT

Variable

A point described by two coordinates. When the coordinates are longitude and latitude, HEAVY.AI stores longitude first, and then latitude. For example: POINT(0 0)

POLYGON

Variable

A set of one or more rings (closed line strings), with the first representing the shape (external ring) and the rest representing holes in that shape (internal rings). For example: POLYGON((0 0,4 0,4 4,0 4,0 0),(1 1, 2 1, 2 2, 1 2,1 1))

MULTIPOINT

Variable

A set of one or more points. For example: MULTIPOINT((0 0), (1 1), (2 2))

MULTILINESTRING

Variable

A set of one or more associated lines, each of two or more points. For example: MULTILINESTRING((0 0, 1 0, 2 0), (0 1, 1 1, 2 1))

For information about geospatial datatype sizes, see Storage and Compression in Datatypes.

For more information on WKT primitives, see Wikipedia: Well-known Text: Geometric objects.

HEAVY.AI supports SRID 4326 (WGS 84) and 900913 (Google Web Mercator), and 32601-32660,32701-32760 (Universal Transverse Mercator (UTM) Zones). When using geospatial fields, you set the SRID to determine which reference system to use. HEAVY.AI does not assign a default SRID.

CREATE TABLE simple_geo (
                          name TEXT ENCODING DICT(32), 
                          location GEOMETRY(POINT,4326)
                         );

If you do not set the SRID of the geo field in the table, you can set it in a SQL query using ST_SETSRID(column_name, SRID). For example, ST_SETSRID(a.pt,4326).

When representing longitude and latitude, the first coordinate is assumed to be longitude in HEAVY.AI geospatial primitives.

You create geospatial objects as geometries (planar spatial data types), which are supported by the planar geometry engine at run time. When you call ST_DISTANCE on two geometry objects, the engine returns the shortest straight-line planar distance, in degrees, between those points. For example, the following query returns the shortest distance between the point(s) in p1 and the polygon(s) in poly1:

SELECT ST_DISTANCE(p1, poly1) FROM geo1;

For information about importing data, see Importing Geospatial Data.

Geospatial Literals

Geospatial functions that expect geospatial object arguments accept geospatial columns, geospatial objects returned by other functions, or string literals containing WKT representations of geospatial objects. Supplying a WKT string is equivalent to calling a geometry constructor. For example, these two queries are identical:

SELECT COUNT(*) FROM geo1 WHERE ST_DISTANCE(p1, `POINT(1 2)`) < 1.0;
SELECT COUNT(*) FROM geo1 WHERE ST_DISTANCE(p1, ST_GeomFromText('POINT(1 2)')) < 1.0;

You can create geospatial literals with a specific SRID. For example:

SELECT ST_CONTAINS(
                     mpoly2, 
                     ST_GeomFromText('POINT(-71.064544 42.28787)', 4326)
                   )
                   FROM geo2;

Support for Geography

HEAVY.AI provides support for geography objects and geodesic distance calculations, with some limitations.

Exporting Coordinates from Immerse

HeavyDB supports import from any coordinate system supported by the Geospatial Data Abstraction Library (GDAL). On import, HeavyDB will convert to and store in WGS84 encoding, and rendering is accurate in Immerse.

However, no built-in way to reference the original coordinates currently exists in Immerse, and coordinates exported from Immerse will be WGS84 coordinates. You can work around this limitation by adding to the dataset a column or columns in non-geo format that could be included for display in Immerse (for example, in a popup) or on export.

Distance Calculation

Currently, HEAVY.AI supports spheroidal distance calculation between:

  • Two points using either SRID 4326 or 900913.

  • A point and a polygon/multipolygon using SRID 900913.

Using SRID 900913 results in variance compared to SRID 4326 as polygons approach the North and South Poles.

The following query returns the points and polygons within 1,000 meters of each other:

SELECT a.poly_name, b.pt_name FROM poly a, pt b 
WHERE ST_Distance(
   ST_Transform(b.heavyai_geo, 900913),
   ST_Transform(b.location, 900913))<1000;

See the tables in Geospatial Functions below for examples.

Geospatial Functions

HEAVY.AI supports the functions listed.

Geometry Constructors

Function

Description

ST_Centroid

Computes the geometric center of a geometry as a POINT.

ST_GeomFromText(WKT)

Return a specified geometry value from Well-known Text representation.

ST_GeomFromText(WKT, SRID)

Return a specified geometry value from Well-known Text representation and an SRID.

ST_GeogFromText(WKT)

Return a specified geography value from Well-known Text representation.

ST_GeogFromText(WKT, SRID)

Return a specified geography value from Well-known Text representation and an SRID.

ST_Point(double lon, double lat)

Return a point constructed on the fly from the provided coordinate values. Constant coordinates result in construction of a POINT literal.

Example: ST_Contains(poly4326, ST_SetSRID(ST_Point(lon, lat), 4326))

Geometry to String Conversion

Function
Description

ST_AsText(geom) | ST_AsWKT(geom)

Converts a geometry input to a Well-Known-Text (WKT) string

ST_AsBinary(geom) | ST_AsWKB(geom)

Converts a geometry input to a Well-Known-Binary (WKB) string

Geometry Processing

Function
Description

ST_Buffer

Returns a geometry covering all points within a specified distance from the input geometry. Performed by the GEOS module. The output is currently limited to the MULTIPOLYGON type.

Calculations are in the units of the input geometry’s SRID. Buffer distance is expressed in the same units. Example:

SELECT ST_Buffer('LINESTRING(0 0, 10 0, 10 10)', 1.0);

Special processing is automatically applied to WGS84 input geometries (SRID=4326) to limit buffer distortion:

  • Implementation first determines the best planar SRID to which to project the 4326 input geometry.

  • Preferred SRIDs are UTM and Lambert (LAEA) North/South zones, with Mercator used as a fallback.

  • Buffer distance is interpreted as distance in meters (units of all planar SRIDs being considered).

  • The input geometry is transformed to the best planar SRID and handed to GEOS, along with buffer distance.

  • The buffer geometry built by GEOS is then transformed back to SRID=4326 and returned.

Example: Build 10-meter buffer geometries (SRID=4326) with limited distortion:

SELECT ST_Buffer(poly4326, 10.0) FROM tbl;

ST_Centroid

Computes the geometric center of a geometry as a POINT.

FunctionDescription Special processing is automatically applied to WGS84 input geometries (SRID=4326) to limit buffer distortion:

  • Implementation first determines the best planar SRID to which to project the 4326 input geometry.

  • Preferred SRIDs are UTM and Lambert (LAEA) North/South zones, with Mercator used as a fallback.

  • Buffer distance is interpreted as distance in meters (units of all planar SRIDs being considered).

  • The input geometry is transformed to the best planar SRID and handed to GEOS, along with buffer distance.

  • The buffer geometry built by GEOS is then transformed back to SRID=4326 and returned.

Example: Build 10-meter buffer geometries (SRID=4326) with limited distortion:SELECT ST_Buffer(poly4326, 10.0) FROM tbl; .ST_CentroidComputes the geometric center of a geometry as a POINT.

Geometry Editors

Function

Description

ST_TRANSFORM

Returns a geometry with its coordinates transformed to a different spatial reference. Currently, WGS84 to Web Mercator transform is supported. For example:ST_DISTANCE( ST_TRANSFORM(ST_GeomFromText('POINT(-71.064544 42.28787)', 4326), 900913), ST_GeomFromText('POINT(-13189665.9329505 3960189.38265416)', 900913) )

ST_TRANSFORM is not currently supported in projections. It can be used only to transform geo inputs to other functions, such as ST_DISTANCE.

ST_SETSRID

Set the SRID to a specific integer value. For example:

ST_TRANSFORM(

ST_SETSRID(ST_GeomFromText('POINT(-71.064544 42.28787)'), 4326), 900913 )

Geometry Accessors

Function

Description

ST_X

Returns the X value from a POINT column.

ST_Y

Returns the Y value from a POINT column.

ST_XMIN

Returns X minima of a geometry.

ST_XMAX

Returns X maxima of a geometry.

ST_YMIN

Returns Y minima of a geometry.

ST_YMAX

Returns Y maxima of a geometry.

ST_STARTPOINT

Returns the first point of a LINESTRING as a POINT.

ST_ENDPOINT

Returns the last point of a LINESTRING as a POINT.

ST_POINTN

Return the Nth point of a LINESTRING as a POINT.

ST_NPOINTS

Returns the number of points in a geometry.

ST_NRINGS

Returns the number of rings in a POLYGON or a MULTIPOLYGON.

ST_SRID

Returns the spatial reference identifier for the underlying object.

ST_NUMGEOMETRIES

Returns the MULTI count of MULTIPOINT, MULTILINESTRING or MULTIPOLYGON. Returns 1 for non-MULTI geometry.

Overlay Functions

Function

Description

ST_INTERSECTION

Returns a geometry representing an intersection of two geometries; that is, the section that is shared between the two input geometries. Performed by the GEOS module.

The output is currently limited to MULTIPOLYGON type, because HEAVY.AI does not support mixed geometry types within a geometry column, and ST_INTERSECTION can potentially return points, lines, and polygons from a single intersection operation. Lower-dimension intersecting features such as points and line strings are returned as very small buffers around those features. If needed, true points can be recovered by applying the ST_CENTROID method to point intersection results. In addition, ST_PERIMETER/2 of resulting line intersection polygons can be used to approximate line length. Empty/NULL geometry outputs are not currently supported.

Examples: SELECT ST_Intersection('POLYGON((0 0,3 0,3 3,0 3))', 'POLYGON((1 1,4 1,4 4,1 4))'); SELECT ST_Area(ST_Intersection(poly, 'POLYGON((1 1,3 1,3 3,1 3,1 1))')) FROM tbl;

ST_DIFFERENCE

Returns a geometry representing the portion of the first input geometry that does not intersect with the second input geometry. Performed by the GEOS module. Input order is important; the return geometry is always a section of the first input geometry.

The output is currently limited to MULTIPOLYGON type, for the same reasons described in ST_INTERSECTION. Similar post-processing methods can be applied if needed. Empty/NULL geometry outputs are not currently supported.

Examples: SELECT ST_Difference('POLYGON((0 0,3 0,3 3,0 3))', 'POLYGON((1 1,4 1,4 4,1 4))'); SELECT ST_Area(ST_Difference(poly, 'POLYGON((1 1,3 1,3 3,1 3,1 1))')) FROM tbl;

ST_UNION

Returns a geometry representing the union (or combination) of the two input geometries. Performed by the GEOS module.

The output is currently limited to MULTIPOLYGON type for the same reasons described in ST_INTERSECTION. Similar post-processing methods can be applied if needed. Empty/NULL geometry outputs are not currently supported.

Examples: SELECT ST_UNION('POLYGON((0 0,3 0,3 3,0 3))', 'POLYGON((1 1,4 1,4 4,1 4))'); SELECT ST_AREA(ST_UNION(poly, 'POLYGON((1 1,3 1,3 3,1 3,1 1))')) FROM tbl;

Spatial Relationships and Measurements

Function

Description

ST_DISTANCE

Returns shortest planar distance between geometries. For example: ST_DISTANCE(poly1, ST_GeomFromText('POINT(0 0)')) Returns shortest geodesic distance between two points, in meters, if given two point geographies. Point geographies can be specified through casts from point geometries or as literals. For example: ST_DISTANCE( CastToGeography(p2), ST_GeogFromText('POINT(2.5559 49.0083)', 4326) )

SELECT a.name, ST_DISTANCE( CAST(a.pt AS GEOGRAPHY), CAST(b.pt AS GEOGRAPHY) ) AS dist_meters FROM starting_point a, destination_points b;

You can also calculate the distance between a POLYGON and a POINT. If both fields use SRID 4326, then the calculated distance is in 4326 units (degrees). If both fields use SRID 4326, and both are transformed into 900913, then the results are in 900913 units (meters).

The following SQL code returns the names of polygons where the distance between the point and polygon is less than 1,000 meters.

SELECT a.poly_name FROM poly a, point b WHERE ST_DISTANCE( ST_TRANSFORM(b.location,900913), ST_TRANSFORM(a.heavyai_geo,900913) ) < 1000;

ST_EQUALS

Returns TRUE if the first input geometry and the second input geometry are spatially equal; that is, they occupy the same space. Different orderings of points can be accepted as equal if they represent the same geometry structure.

POINTs comparison is performed natively. All other geometry comparisons are performed by GEOS.

If input geometries are both uncompressed or compressed, all comparisons to identify equality are precise. For mixed combinations, the comparisons are performed with a compression-specific tolerance that allows recognition of equality despite subtle precision losses that the compression may introduce. Note: Geo columns and literals with SRID=4326 are compressed by default.

Examples: SELECT COUNT(*) FROM tbl WHERE ST_EQUALS('POINT(2 2)', pt); SELECT ST_EQUALS('POLYGON ((0 0,1 0,0 1))', 'POLYGON ((0 0,0 0.5,0 1,1 0,0 0))');

ST_MAXDISTANCE

Returns longest planar distance between geometries. In effect, this is the diameter of a circle that encloses both geometries.For example:

Currently supported variants:

ST_CONTAINS

Returns true if the first geometry object contains the second object. For example:

You can also use ST_CONTAINS to:

  • Return the count of polys that contain the point (here as WKT): SELECT count(*) FROM geo1 WHERE ST_CONTAINS(poly1, 'POINT(0 0)');

  • Return names from a polys table that contain points in a points table: SELECT a.name FROM polys a, points b WHERE ST_CONTAINS(a.heavyai_geo, b.location);

  • Return names from a polys table that contain points in a points table, using a single point in WKT instead of a field in another table: SELECT name FROM poly WHERE ST_CONTAINS( heavyai_geo, ST_GeomFromText('POINT(-98.4886935 29.4260508)', 4326) );

ST_INTERSECTS

Returns true if two geometries intersect spatially, false if they do not share space. For example:

SELECT ST_INTERSECTS( 'POLYGON((0 0, 2 0, 2 2, 0 2, 0 0))', 'POINT(1 1)' ) FROM tbl;

ST_AREA

Returns the area of planar areas covered by POLYGON and MULTIPOLYGON geometries. For example:

SELECT ST_AREA( 'POLYGON((1 0, 0 1, -1 0, 0 -1, 1 0),(0.1 0, 0 0.1, -0.1 0, 0 -0.1, 0.1 0))' ) FROM tbl;

ST_AREA does not support calculation of geographic areas, but rather uses planar coordinates. Geographies must first be projected in order to use ST_AREA. You can do this ahead of time before import or at runtime, ideally using an equal area projection (for example, a national equal-area Lambert projection). The area is calculated in the projection's units. For example, you might use Web Mercator runtime projection to get the area of a polygon in square meters:

ST_AREA( ST_TRANSFORM( ST_GeomFromText( 'POLYGON((-76.6168198439371 39.9703199555959, -80.5189990254673 40.6493554919257, -82.5189990254673 42.6493554919257, -76.6168198439371 39.9703199555959) )', 4326 ), 900913) )

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Web Mercator is not an equal area projection, however. Unless compensated by a scaling factor, Web Mercator areas can vary considerably by latitude.

ST_PERIMETER

Returns the cartesian perimeter of POLYGON and MULTIPOLYGON geometries. For example: SELECT ST_PERIMETER('POLYGON( (1 0, 0 1, -1 0, 0 -1, 1 0), (0.1 0, 0 0.1, -0.1 0, 0 -0.1, 0.1 0) )' ) from tbl; It will also return the geodesic perimeter of POLYGON and MULTIPOLYGON geometries. For example:

SELECT ST_PERIMETER( ST_GeogFromText( 'POLYGON( (-76.6168198439371 39.9703199555959, -80.5189990254673 40.6493554919257, -82.5189990254673 42.6493554919257, -76.6168198439371 39.9703199555959) )', 4326) ) from tbl;

ST_LENGTH

Returns the cartesian length of LINESTRING geometries. For example: SELECT ST_LENGTH('LINESTRING(1 0, 0 1, -1 0, 0 -1, 1 0)') FROM tbl; It also returns the geodesic length of LINESTRING geographies. For example:

SELECT ST_LENGTH( ST_GeogFromText('LINESTRING( -76.6168198439371 39.9703199555959, -80.5189990254673 40.6493554919257, -82.5189990254673 42.6493554919257)', 4326) ) FROM tbl;

ST_WITHIN

Returns true if geometry A is completely within geometry B. For example the following SELECT statement returns true:

SELECT ST_WITHIN( 'POLYGON ((1 1, 1 2, 2 2, 2 1))', 'POLYGON ((0 0, 0 3, 3 3, 3 0))' ) FROM tbl;

ST_DWITHIN

Returns true if the geometries are within the specified distance of each one another. Distance is specified in units defined by the spatial reference system of the geometries. For example: SELECT ST_DWITHIN( 'POINT(1 1)', 'LINESTRING (1 2,10 10,3 3)', 2.0 ) FROM tbl; ST_DWITHIN supports geodesic distances between geographies, currently limited to geographic points. For example, you can check whether Los Angeles and Paris, specified as WGS84 geographic point literals, are within 10,000km of one another.

SELECT ST_DWITHIN(

ST_GeogFromText( 'POINT(-118.4079 33.9434)', 4326), ST_GeogFromText('POINT(2.5559 49.0083)', 4326 ), 10000000.0) FROM tbl;

ST_DFULLYWITHIN

Returns true if the geometries are fully within the specified distance of one another. Distance is specified in units defined by the spatial reference system of the geometries. For example: SELECT ST_DFULLYWITHIN( 'POINT(1 1)', 'LINESTRING (1 2,10 10,3 3)', 10.0) FROM tbl; This function supports:

ST_DFULLYWITHIN(POINT, LINESTRING, distance) ST_DFULLYWITHIN(LINESTRING, POINT, distance)

ST_DISJOINT

Returns true if the geometries are spatially disjoint (that is, the geometries do not overlap or touch. For example:

SELECT ST_DISJOINT( 'POINT(1 1)', 'LINESTRING (0 0,3 3)' ) FROM tbl;

Additional Geo Notes

  • You can use SQL code similar to the examples in this topic as global filters in Immerse.

  • CREATE TABLE AS SELECT is not currently supported for geo data types in distributed mode.

  • GROUP BY is not supported for geo types (POINT, MULTIPOINT, LINESTRING, MULTILINESTRING, POLYGON, or MULTIPOLYGON.

  • You can use \d table_name to determine if the SRID is set for the geo field:

    heavysql> \d starting_point
CREATE TABLE starting_point (
                               name TEXT ENCODING DICT(32),
                               myPoint GEOMETRY(POINT, 4326) ENCODING COMPRESSED(32)
                             )

    If no SRID is returned, you can set the SRID using ST_SETSRID(column_name, SRID). For example, ST_SETSRID(myPoint, 4326).

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