unaryUnion

Computes the (self) union of all components of geometry a. This is particularly useful for reducing MultiGeometries or GeometryCollections into their minimal representation, merging overlapping elements and removing duplicates.

Parameters

Name	Type	Description
a	Geometry	Geometry
options?	object	Optional options object
options.gridSize?	number	Precision grid cell size for snapping vertices. If 0 or when not defined, the highest precision is used (IEE754 double), which provides almost 16 decimal digits of precision. If nonzero, input as well as resulting coordinates will be snapped to a precision grid of that size.

Returns

Geometry

A new geometry representing the union of all components

Examples

dissolving overlapping polygons in a MultiPolygon

const a = fromWKT('MULTIPOLYGON (((0 0, 0 10, 10 10, 10 0, 0 0), (1 9, 8 8, 9 1, 1 9)), ((5 10, 15 15, 10 5, 5 10)))');
const a_uUnion = unaryUnion(a);
// 'POLYGON ((0 10, 5 10, 15 15, 10 5, 10 0, 0 0, 0 10), (1 9, 9 1, 8.166666666666666 6.833333333333333, 6.833333333333333 8.166666666666666, 1 9))'
const a_uUnion_pg = unaryUnion(a, { gridSize: 1e-4 });
// 'POLYGON ((0 10, 5 10, 15 15, 10 5, 10 0, 0 0, 0 10), (1 9, 9 1, 8.1667 6.8333, 6.8333 8.1667, 1 9))'

const a = fromWKT('MULTIPOLYGON (((0 0, 0 10, 10 10, 10 0, 0 0), (1 9, 8 8, 9 1, 1 9)), ((5 10, 15 15, 10 5, 5 10)))'); const a_uUnion = unaryUnion(a); // 'POLYGON ((0 10, 5 10, 15 15, 10 5, 10 0, 0 0, 0 10), (1 9, 9 1, 8.166666666666666 6.833333333333333, 6.833333333333333 8.166666666666666, 1 9))' const a_uUnion_pg = unaryUnion(a, { gridSize: 1e-4 }); // 'POLYGON ((0 10, 5 10, 15 15, 10 5, 10 0, 0 0, 0 10), (1 9, 9 1, 8.1667 6.8333, 6.8333 8.1667, 1 9))'

should remove duplicated points

const a = multiPoint([ [ 4, 5 ], [ 6, 7 ], [ 4, 5 ], [ 6, 5 ], [ 6, 7 ] ]);
const a_uUnion = unaryUnion(a); // 'MULTIPOINT ((4 5), (6 5), (6 7))'
const a_uUnion_pg = unaryUnion(a, { gridSize: 2 }); // 'MULTIPOINT ((4 6), (6 6), (6 8))'

const a = multiPoint([ [ 4, 5 ], [ 6, 7 ], [ 4, 5 ], [ 6, 5 ], [ 6, 7 ] ]); const a_uUnion = unaryUnion(a); // 'MULTIPOINT ((4 5), (6 5), (6 7))' const a_uUnion_pg = unaryUnion(a, { gridSize: 2 }); // 'MULTIPOINT ((4 6), (6 6), (6 8))'