geo_polygon_simplify()

  • Article

Simplifies a polygon or a multipolygon by replacing nearly straight chains of short edges with a single long edge on Earth.

Syntax

geo_polygon_simplify(polygon, tolerance)

Learn more about syntax conventions.

Parameters

Name Type Required Description
polygon dynamic ✔️ Polygon or multipolygon in the GeoJSON format.
tolerance int, long, or real Defines maximum distance in meters between the original planar edge and the converted geodesic edge chain. Supported values are in the range [0.1, 10000]. If unspecified, the default value is 10.

Returns

Simplified polygon or a multipolygon in the GeoJSON format and of a dynamic data type, with no two vertices with distance less than tolerance. If either the polygon or tolerance is invalid, the query will produce a null result.

Note

  • If input has more than one polygon, with mutual borders, please see geo_simplify_polygons_array().
  • 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.
  • If input is a multipolygon and contains more than one polygon, the result will be the area of polygons union.
  • High tolerance may cause small polygon to disappear.

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.

Examples

The following example simplifies polygons by removing vertices that are within a 10-meter distance from each other.

Run the query

let polygon = dynamic({"type":"Polygon","coordinates":[[[-73.94885122776031,40.79673476355657],[-73.94885927438736,40.79692258628347],[-73.94887939095497,40.79692055577034],[-73.9488673210144,40.79693476936093],[-73.94888743758202,40.79693476936093],[-73.9488834142685,40.796959135509105],[-73.94890084862709,40.79695304397289],[-73.94906312227248,40.79710736271788],[-73.94923612475395,40.7968708081794],[-73.94885122776031,40.79673476355657]]]});
print simplified = geo_polygon_simplify(polygon)

Output

simplified
{"type": "Polygon", "coordinates": [[[-73.948851227760315, 40.796734763556572],[-73.949063122272477, 40.797107362717881],[-73.949236124753952, 40.7968708081794],[-73.948851227760315, 40.796734763556572]]]}

The following example simplifies polygons and combines results into GeoJSON geometry collection.

Polygons
| project polygon = features.geometry
| project simplified = geo_polygon_simplify(polygon, 1000)
| summarize lst = make_list(simplified)
| project geojson = bag_pack("type", "Feature","geometry", bag_pack("type", "GeometryCollection", "geometries", lst), "properties", bag_pack("name", "polygons"))

Output

geojson
{"type": "Feature", "geometry": {"type": "GeometryCollection", "geometries": [ ... ]}, "properties": {"name": "polygons"}}

The following example simplifies polygons and unifies result

Run the query

US_States
| project polygon = features.geometry
| project simplified = geo_polygon_simplify(polygon, 1000)
| summarize lst = make_list(simplified)
| project polygons = geo_union_polygons_array(lst)

Output

polygons
{"type": "MultiPolygon", "coordinates": [ ... ]}

The following example returns True because of the invalid polygon.

Run the query

let polygon = dynamic({"type":"Polygon","coordinates":[[[5,48],[5,48]]]});
print is_invalid_polygon = isnull(geo_polygon_simplify(polygon))

Output

is_invalid_polygon
1

The following example returns True because of the invalid tolerance.

Run the query

let polygon = dynamic({"type":"Polygon","coordinates":[[[5,48],[0,50],[0,47],[4,47],[5,48]]]});
print is_invalid_polygon = isnull(geo_polygon_simplify(polygon, -0.1))

Output

is_invalid_polygon
1

The following example returns True because high tolerance causes polygon to disappear.

Run the query

let polygon = dynamic({"type":"Polygon","coordinates":[[[5,48],[0,50],[0,47],[4,47],[5,48]]]});
print is_invalid_polygon = isnull(geo_polygon_simplify(polygon, 1000000))

Output

is_invalid_polygon
1