@flatten-js/polygon-offset

Offset polygon

This package implements algorithm of equidistant offset of polygon. It relies on the flatten-js library and its polygon model.

Algorithm based on the idea of morphological offset, when each edge of the polygon is mapped to its offset, and then boolean operation performed between original contour and offset edges. When offset value is positive, offset edges are unified with original contour, when negative - they are subtracted from original contour.

Contacts

Follow me on Twitter @alex_bol_

Installation

    npm install --save @flatten-js/polygon-offset

The package @flatten-js/core is peer dependency of this package and have to be installed separately:

    npm install --save @flatten-js/core

Usage

    import offset from "@flatten-js/polygon-offset"

    let offsetPolygon = offset(polygon, offset_value)

Example:

    import {segment, point, Polygon} from "@flatten-js/core"
    import offset from "@flatten-js/polygon-offset"

    // Create polygon
    let shapes = [
            segment(point(200,100), point(200,300)),
            segment(point(200,300), point(440,300)),
            segment(point(440,300), point(300,200)),
            segment(point(300,200), point(440,150)),
            segment(point(440,150), point(500,150)),
            segment(point(500,150), point(640,200)),
            segment(point(640,200), point(500,300)),
            segment(point(500,300), point(740,300)),
            segment(point(740,300), point(740,100)),
            segment(point(740,100), point(200,100))
        ];
    
    let polygon = new Polygon();
    polygon.addFace(shapes);
    
    // Apply polygon offset
    let offsetPolygon = offset(polygon, 20);