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Introduction to Stream Analytics geospatial functions

  • Artikkeli

Geospatial functions in Azure Stream Analytics enable real-time analytics on streaming geospatial data. With just a few lines of code, you can develop a production grade solution for complex scenarios. These functions support all WKT types and GeoJSON Point, Polygon, and LineString.

Examples of scenarios that can benefit from geospatial functions include:

  • Ride-sharing
  • Fleet management
  • Asset tracking
  • Geo-fencing
  • Phone tracking across cell sites

Stream Analytics Query Language has seven built-in geospatial functions: CreateLineString, CreatePoint, CreatePolygon, ST_DISTANCE, ST_OVERLAPS, ST_INTERSECTS, and ST_WITHIN.

CreateLineString

The CreateLineString function accepts points and returns a GeoJSON LineString, which can be plotted as a line on a map. You must have at least two points to create a LineString. The LineString points will be connected in order.

The following query uses CreateLineString to create a LineString using three points. The first point is created from streaming input data, while the other two are created manually.

SELECT  
     CreateLineString(CreatePoint(input.latitude, input.longitude), CreatePoint(10.0, 10.0), CreatePoint(10.5, 10.5))  
FROM input

Input example

latitude longitude
3.0 -10.2
-87.33 20.2321

Output example

{"type" : "LineString", "coordinates" : [ [-10.2, 3.0], [10.0, 10.0], [10.5, 10.5] ]}

{"type" : "LineString", "coordinates" : [ [20.2321, -87.33], [10.0, 10.0], [10.5, 10.5] ]}

To learn more, visit the CreateLineString reference.

CreatePoint

The CreatePoint function accepts a latitude and longitude and returns a GeoJSON point, which can be plotted on a map. Your latitudes and longitudes must be a float datatype.

The following example query uses CreatePoint to create a point using latitudes and longitudes from streaming input data.

SELECT  
     CreatePoint(input.latitude, input.longitude)  
FROM input

Input example

latitude longitude
3.0 -10.2
-87.33 20.2321

Output example

{"type" : "Point", "coordinates" : [-10.2, 3.0]}

{"type" : "Point", "coordinates" : [20.2321, -87.33]}

To learn more, visit the CreatePoint reference.

CreatePolygon

The CreatePolygon function accepts points and returns a GeoJSON polygon record. The order of points must follow right-hand ring orientation, or counter-clockwise. Imagine walking from one point to another in the order they were declared. The center of the polygon would be to your left the entire time.

The following example query uses CreatePolygon to create a polygon from three points. The first two points are created manually, and the last point is created from input data.

SELECT  
     CreatePolygon(CreatePoint(input.latitude, input.longitude), CreatePoint(10.0, 10.0), CreatePoint(10.5, 10.5), CreatePoint(input.latitude, input.longitude))  
FROM input

Input example

latitude longitude
3.0 -10.2
-87.33 20.2321

Output example

{"type" : "Polygon", "coordinates" : [[ [-10.2, 3.0], [10.0, 10.0], [10.5, 10.5], [-10.2, 3.0] ]]}

{"type" : "Polygon", "coordinates" : [[ [20.2321, -87.33], [10.0, 10.0], [10.5, 10.5], [20.2321, -87.33] ]]}

To learn more, visit the CreatePolygon reference.

ST_DISTANCE

The ST_DISTANCE function returns the distance between two geometries in meters.

The following query uses ST_DISTANCE to generate an event when a gas station is less than 10 km from the car.

SELECT Cars.Location, Station.Location 
FROM Cars c  
JOIN Station s ON ST_DISTANCE(c.Location, s.Location) < 10 * 1000

To learn more, visit the ST_DISTANCE reference.

ST_OVERLAPS

The ST_OVERLAPS function compares two geometries. If the geometries overlap, the function returns a 1. The function returns 0 if the geometries don't overlap.

The following query uses ST_OVERLAPS to generate an event when a building is within a possible flooding zone.

SELECT Building.Polygon, Building.Polygon 
FROM Building b 
JOIN Flooding f ON ST_OVERLAPS(b.Polygon, b.Polygon)

The following example query generates an event when a storm is heading towards a car.

SELECT Cars.Location, Storm.Course
FROM Cars c, Storm s
JOIN Storm s ON ST_OVERLAPS(c.Location, s.Course)

To learn more, visit the ST_OVERLAPS reference.

ST_INTERSECTS

The ST_INTERSECTS function compares two geometries. If the geometries intersect, then the function returns 1. The function returns 0 if the geometries don't intersect each other.

The following example query uses ST_INTERSECTS to determine if a paved road intersects a dirt road.

SELECT  
     ST_INTERSECTS(input.pavedRoad, input.dirtRoad)  
FROM input

Input example

datacenterArea stormArea
{"type":"LineString", "coordinates": [ [-10.0, 0.0], [0.0, 0.0], [10.0, 0.0] ]} {"type":"LineString", "coordinates": [ [0.0, 10.0], [0.0, 0.0], [0.0, -10.0] ]}
{"type":"LineString", "coordinates": [ [-10.0, 0.0], [0.0, 0.0], [10.0, 0.0] ]} {"type":"LineString", "coordinates": [ [-10.0, 10.0], [0.0, 10.0], [10.0, 10.0] ]}

Output example

1

0

To learn more, visit the ST_INTERSECTS reference.

ST_WITHIN

The ST_WITHIN function determines whether a geometry is within another geometry. If the first is contained in the last, the function will return 1. The function will return 0 if the first geometry isn't located within the last one.

The following example query uses ST_WITHIN to determine whether the delivery destination point is within the given warehouse polygon.

SELECT  
     ST_WITHIN(input.deliveryDestination, input.warehouse)  
FROM input

Input example

deliveryDestination warehouse
{"type":"Point", "coordinates": [76.6, 10.1]} {"type":"Polygon", "coordinates": [ [0.0, 0.0], [10.0, 0.0], [10.0, 10.0], [0.0, 10.0], [0.0, 0.0] ]}
{"type":"Point", "coordinates": [15.0, 15.0]} {"type":"Polygon", "coordinates": [ [10.0, 10.0], [20.0, 10.0], [20.0, 20.0], [10.0, 20.0], [10.0, 10.0] ]}

Output example

0

1

To learn more, visit the ST_WITHIN reference.

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