Geospatial Capabilities
HEAVY.AI supports a subset of object types and functions for storing and writing queries for geospatial definitions.
Geospatial Datatypes
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.
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
:
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:
You can create geospatial literals with a specific SRID. For example:
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:
See the tables in Geospatial Functions below for examples.
Geospatial Functions
HEAVY.AI supports the functions listed.
Geometry Constructors
Geometry to String Conversion
Geometry Processing
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_Centroid
Computes the geometric center of a geometry as a POINT.
Geometry Editors
Geometry Accessors
Overlay Functions
Spatial Relationships and Measurements
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
, orMULTIPOLYGON
.You can use
\d table_name
to determine if the SRID is set for the geo field: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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