simplify

Computes a simplified representation of a geometry using the Douglas-Peucker algorithm.

Simplification reduces the number of vertices by removing those which are within the tolerance distance of the simplified linework.

The simplification tolerance is in input geometry units.

Parameters

Name	Type	Default	Description
geometry	Geometry		The geometry to simplify
tolerance	number		The maximum allowed deviation - any vertex within this distance of the simplified linework is removed
options?	object		Optional options object
options.preserveTopology?	boolean	true	Whether to preserve the original topology during simplification. When true, a topology‐preserving variant of the Douglas–Peucker algorithm is used. The output will be valid and simple if the input is. This option is computationally more expensive. When false, the standard Douglas–Peucker simplification is used, which may produce invalid or self‐intersecting geometries.

Returns

Geometry

A new, simplified, geometry without "unnecessary" vertices

Throws

• GEOSError when tolerance is negative
• GEOSError on unsupported geometry types (curved)

Examples

const o1 = multiLineString([
    [ [ 10, 60 ], [ 39, 50 ], [ 70, 60 ], [ 90, 53 ] ],
    [ [ 35, 55 ], [ 46, 55 ] ],
    [ [ 65, 55 ], [ 75, 55 ] ],
    [ [ 10, 40 ], [ 40, 30 ], [ 70, 40 ], [ 90, 30 ] ],
]);
const s1 = simplify(o1, 10);

const o2 = multiLineString([
    [ [ 110, 60 ], [ 139, 50 ], [ 170, 60 ], [ 190, 53 ] ],
    [ [ 135, 55 ], [ 146, 55 ] ],
    [ [ 165, 55 ], [ 175, 55 ] ],
    [ [ 110, 40 ], [ 140, 30 ], [ 170, 40 ], [ 190, 30 ] ],
]);
const s2 = simplify(o2, 10, { preserveTopology: false });

const o1 = multiLineString([ [ [ 10, 60 ], [ 39, 50 ], [ 70, 60 ], [ 90, 53 ] ], [ [ 35, 55 ], [ 46, 55 ] ], [ [ 65, 55 ], [ 75, 55 ] ], [ [ 10, 40 ], [ 40, 30 ], [ 70, 40 ], [ 90, 30 ] ], ]); const s1 = simplify(o1, 10); const o2 = multiLineString([ [ [ 110, 60 ], [ 139, 50 ], [ 170, 60 ], [ 190, 53 ] ], [ [ 135, 55 ], [ 146, 55 ] ], [ [ 165, 55 ], [ 175, 55 ] ], [ [ 110, 40 ], [ 140, 30 ], [ 170, 40 ], [ 190, 30 ] ], ]); const s2 = simplify(o2, 10, { preserveTopology: false });

const o1 = multiPolygon([
    [
        [ [ 10, 10 ], [ 10, 20 ], [ 20, 70 ], [ 10, 80 ], [ 20, 80 ], [ 50, 90 ], [ 70, 80 ], [ 90, 80 ], [ 85, 20 ], [ 90, 10 ], [ 50, 0 ], [ 10, 10 ] ],
        [ [ 80, 20 ], [ 20, 20 ], [ 50, 90 ], [ 80, 20 ] ],
        [ [ 30, 9 ], [ 70, 9 ], [ 50, 0 ], [ 30, 9 ] ],
    ],
    [ [ [ 0, 50 ], [ 0, 75 ], [ 15, 65 ], [ 5, 30 ], [ 0, 50 ] ] ],
    [ [ [ 90, 20 ], [ 95, 60 ], [ 95, 10 ], [ 90, 20 ] ] ],
]);
const s1 = simplify(o1, 10);

const o2 = multiPolygon([
    [
        [ [ 130, 10 ], [ 130, 20 ], [ 140, 70 ], [ 130, 80 ], [ 140, 80 ], [ 170, 90 ], [ 190, 80 ], [ 210, 80 ], [ 205, 20 ], [ 210, 10 ], [ 170, 0 ], [ 130, 10 ] ],
        [ [ 200, 20 ], [ 140, 20 ], [ 170, 90 ], [ 200, 20 ] ],
        [ [ 150, 9 ], [ 190, 9 ], [ 170, 0 ], [ 150, 9 ] ],
    ],
    [ [ [ 120, 50 ], [ 120, 75 ], [ 135, 65 ], [ 125, 30 ], [ 120, 50 ] ] ],
    [ [ [ 210, 20 ], [ 215, 60 ], [ 215, 10 ], [ 210, 20 ] ] ],
]);
const s2 = simplify(o2, 10, { preserveTopology: false });

const o1 = multiPolygon([ [ [ [ 10, 10 ], [ 10, 20 ], [ 20, 70 ], [ 10, 80 ], [ 20, 80 ], [ 50, 90 ], [ 70, 80 ], [ 90, 80 ], [ 85, 20 ], [ 90, 10 ], [ 50, 0 ], [ 10, 10 ] ], [ [ 80, 20 ], [ 20, 20 ], [ 50, 90 ], [ 80, 20 ] ], [ [ 30, 9 ], [ 70, 9 ], [ 50, 0 ], [ 30, 9 ] ], ], [ [ [ 0, 50 ], [ 0, 75 ], [ 15, 65 ], [ 5, 30 ], [ 0, 50 ] ] ], [ [ [ 90, 20 ], [ 95, 60 ], [ 95, 10 ], [ 90, 20 ] ] ], ]); const s1 = simplify(o1, 10); const o2 = multiPolygon([ [ [ [ 130, 10 ], [ 130, 20 ], [ 140, 70 ], [ 130, 80 ], [ 140, 80 ], [ 170, 90 ], [ 190, 80 ], [ 210, 80 ], [ 205, 20 ], [ 210, 10 ], [ 170, 0 ], [ 130, 10 ] ], [ [ 200, 20 ], [ 140, 20 ], [ 170, 90 ], [ 200, 20 ] ], [ [ 150, 9 ], [ 190, 9 ], [ 170, 0 ], [ 150, 9 ] ], ], [ [ [ 120, 50 ], [ 120, 75 ], [ 135, 65 ], [ 125, 30 ], [ 120, 50 ] ] ], [ [ [ 210, 20 ], [ 215, 60 ], [ 215, 10 ], [ 210, 20 ] ] ], ]); const s2 = simplify(o2, 10, { preserveTopology: false });