geo_polygon_buffer()

  • Article

Applies to: ✅ Azure Data Explorer ✅ Azure Monitor ✅ Microsoft Sentinel

Calculates polygon or multipolygon that contains all points within the given radius of the input polygon or multipolygon on Earth.

Syntax

geo_polygon_buffer(polygon, radius, tolerance)

Learn more about syntax conventions.

Parameters

Name Type Required Description
polygon dynamic ✔️ Polygon or multipolygon in the GeoJSON format.
radius real ✔️ Buffer radius in meters. Valid value must be positive.
tolerance real Defines the tolerance in meters that determines how much a polygon can deviate from the ideal radius. If unspecified, the default value 10 is used. Tolerance should be no lower than 0.0001% of the radius. Specifying tolerance bigger than radius will lower the tolerance to biggest possible value below the radius.

Returns

Polygon or MultiPolygon around the input Polygon or multipolygon. If the coordinates or radius or tolerance is invalid, the query will produce a null result.

Note

  • The geospatial coordinates are interpreted as represented by the WGS-84 coordinate reference system.
  • The geodetic datum used for measurements on Earth is a sphere. Polygon edges are geodesics on the sphere.
  • If input polygon edges are straight cartesian lines, consider using geo_polygon_densify() to convert planar edges to geodesics.

Polygon definition and constraints

dynamic({"type": "Polygon","coordinates": [LinearRingShell, LinearRingHole_1, ..., LinearRingHole_N]})

dynamic({"type": "MultiPolygon","coordinates": [[LinearRingShell, LinearRingHole_1, ..., LinearRingHole_N], ..., [LinearRingShell, LinearRingHole_1, ..., LinearRingHole_M]]})

  • LinearRingShell is required and defined as a counterclockwise ordered array of coordinates [[lng_1,lat_1], ..., [lng_i,lat_i], ...,[lng_j,lat_j], ...,[lng_1,lat_1]]. There can be only one shell.
  • LinearRingHole is optional and defined as a clockwise ordered array of coordinates [[lng_1,lat_1], ...,[lng_i,lat_i], ...,[lng_j,lat_j], ...,[lng_1,lat_1]]. There can be any number of interior rings and holes.
  • LinearRing vertices must be distinct with at least three coordinates. The first coordinate must be equal to the last. At least four entries are required.
  • Coordinates [longitude, latitude] must be valid. Longitude must be a real number in the range [-180, +180] and latitude must be a real number in the range [-90, +90].
  • LinearRingShell encloses at most half of the sphere. LinearRing divides the sphere into two regions. The smaller of the two regions will be chosen.
  • LinearRing edge length must be less than 180 degrees. The shortest edge between the two vertices will be chosen.
  • LinearRings must not cross and must not share edges. LinearRings may share vertices.
  • Polygon contains its vertices.

Examples

The following query calculates polygon around input polygon, with radius of 10km.

let polygon = dynamic({"type":"Polygon","coordinates":[[[139.813757,35.719666],[139.72558,35.71813],[139.727471,35.653231],[139.818721,35.657264],[139.813757,35.719666]]]});
print buffer = geo_polygon_buffer(polygon, 10000)
buffer
{"type": "Polygon","coordinates": [ ... ]}

The following query calculates buffer around each polygon and unifies result

datatable(polygon:dynamic, radius:real )
[
    dynamic({"type":"Polygon","coordinates":[[[12.451218693639277,41.906457003556625],[12.445753852969375,41.90160968881543],[12.453514425793855,41.90361551885886],[12.451218693639277,41.906457003556625]]]}), 100,
    dynamic({"type":"Polygon","coordinates":[[[12.4566086734784,41.905119850039995],[12.453913683559591,41.903652663265234],[12.455485761012113,41.90146110630562],[12.4566086734784,41.905119850039995]]]}), 20
]
| project buffer = geo_polygon_buffer(polygon, radius)
| summarize polygons = make_list(buffer)
| project result = geo_union_polygons_array(polygons)
result
{"type": "Polygon","coordinates": [ ... ]}

The following example will return true, due to invalid polygon.

print buffer = isnull(geo_polygon_buffer(dynamic({"type":"p"}), 1))
buffer
True

The following example will return true, due to invalid radius.

print buffer = isnull(geo_polygon_buffer(dynamic({"type":"Polygon","coordinates":[[[10,10],[0,10],[0,0],[10,10]]]}), 0))
buffer
True