Geospatial types

The EPL language has been extended to support additional Geospatial features. All these geospacial features use the WGS84 reference. The types and methods come from the Geotools framework.


Geometry type

This is the base type of all the other geometry shapes.

Point type

Current NGSI v1 protocol only support defining a single location, the geo:point attribute type, that is internally converted to a Geotools Point class.

Polygon type

For handling geofencing features, the CEP also handles the Polygon type which is defined as a list of Point elements defining a closed shape (with identical first and last Point).

The Polygon type cannot be converted to and from the NGSI protocol (yet). It can only be defined from the EPL statements (using create variable statements) during the configuration of the CEP.


Point point(x, y)

This method initializes a new Point with two coordinates.


CREATE VARIABLE Geometry centerPoint = point(4.2, 46.2)

Polygon poly([Point])

This methods takes an array of Point and intializes a Polygon. The first and last point must be identical to close the shape.


CREATE VARIABLE Geometry fence = polygon({point(0, 0), point(0,50), point(50,50), point(50, 0), point(0, 0)})

Note: the syntax to declare an array of element in EPL is { elem1, elem2, ...}.

Geometry read(string)

The read method allows to create any Geometry supported by Geotools using the WKT format.


CREATE VARIABLE Geometry fence2 = geometry("POLYGON((20 10, 30 0, 40 10, 30 20, 20 10))")

Geometry methods

Several methods apply to the Geometry type (and therefore to Pointand Polygon subtypes).

double distance(Geometry)

Compute the distance (expressed in meter) between two Geometry shapes.

Example: Let's track all sensor's location witch are less than 20m far from a center location over the last 10 min:

CREATE VARIABLE Geometry center = point(4.2, 46.2)
INSERT INTO NearbySensors SELECT id, location.distance(center) as distance FROM min) WHERE location.distance(center) < 20

The location method can also be used to compute the distance of a Point to a Polygon.

boolean contains(Geometry)

Return true if the Geometry is contained inside another one.

Example: Let's track when a sensor location is inside a given geofence.

CREATE VARIABLE Geometry fence = polygon({point(0, 0), point(0,50), point(50,50), point(50, 0), point(0, 0)})
INSERT INTO InsideFence SELECT * FROM Sensors WHERE fence.contains(location)