isSimple

Returns true when the geometry is simple as defined by the OGC SFS (Simple Feature Specification). Simple means that any self-intersections are only at boundary points. Mostly relevant for line strings.

Simplicity is defined for each Geometry type as follows:

• Point geometries are simple
• MultiPoint geometries are simple if every point is unique
• LineString geometries are simple if they do not self-intersect at interior points (i.e. points other than the endpoints). LinearRings - closed line strings which intersect only at their endpoints are simple
• MultiLineString geometries are simple if their elements are simple and they intersect only at points which are boundary points of both elements
• Polygonal geometries have no definition of simplicity. The isSimple code checks if all polygon rings are simple. This means that isSimple cannot be used to test for ALL self-intersections in Polygons. Use isValid to check polygonal geometries for self-intersections
• GeometryCollection geometries are simple if all their elements are simple
• Empty geometries are simple

Parameters

Name	Type	Description
geometry	Geometry	The geometry to check

Returns

boolean

true when geometry is simple, false otherwise

Throws

• GEOSError on unsupported geometry types (curved)

See also

• isValid checks whether a geometry is well-formed

Examples

const a = lineString([ [ 0, 0 ], [ 2, 2 ], [ 1, 2 ], [ 1, 0 ] ]);
const a_simple = isSimple(a); // false - self-intersection

const b = multiLineString([ [ [ 2, 0 ], [ 4, 2 ] ], [ [ 3, 2 ], [ 4, 2 ] ] ]);
const b_simple = isSimple(b); // true - intersection at endpoints is ok

const c = lineString([ [ 4, 0 ], [ 5, 1 ], [ 5, 2 ], [ 6, 1 ], [ 5, 1 ] ]);
const c_simple = isSimple(c); // false - intersection not at the endpoints

const d = lineString([ [ 7, 1 ], [ 7, 2 ], [ 8, 1 ], [ 7, 1 ] ]);
const d_simple = isSimple(d); // true - ring

const a = lineString([ [ 0, 0 ], [ 2, 2 ], [ 1, 2 ], [ 1, 0 ] ]); const a_simple = isSimple(a); // false - self-intersection const b = multiLineString([ [ [ 2, 0 ], [ 4, 2 ] ], [ [ 3, 2 ], [ 4, 2 ] ] ]); const b_simple = isSimple(b); // true - intersection at endpoints is ok const c = lineString([ [ 4, 0 ], [ 5, 1 ], [ 5, 2 ], [ 6, 1 ], [ 5, 1 ] ]); const c_simple = isSimple(c); // false - intersection not at the endpoints const d = lineString([ [ 7, 1 ], [ 7, 2 ], [ 8, 1 ], [ 7, 1 ] ]); const d_simple = isSimple(d); // true - ring