Circle To Polygon

The GeoJSON spec does not support circles. If you wish to create an area that represents a circle, your best bet is to create a polygon that roughly approximates the circle. In the limit of the number of edges becoming infinite, your Polygon will match a circle.

Installation

npm install --save circle-to-polygon

or

yarn add circle-to-polygon

Usage

Example

const circleToPolygon = require('circle-to-polygon');

const coordinates = [-27.4575887, -58.99029]; //[lon, lat]
const radius = 100;                           // in meters
const numberOfEdges = 32;                     //optional that defaults to 32

let polygon = circleToPolygon(coordinates, radius, numberOfEdges);

/*
 *
polygon:
 
 type = 'Polygon'
 coordinates = [ [ [ -27.457588699999995, -58.98939168471588 ],
                    [ -27.457248533454194, -58.98940894514629 ],
                    [ -27.456921438327615, -58.9894600631796 ],
                    [ -27.45661998386292, -58.98954307452298 ],
                    [ -27.4563557542251, -58.989654789313285 ],
                    [ -27.456138903413915, -58.98979091466893 ],
                    [ -27.45597776508136, -58.98994621962397 ],
                    [ -27.45587853224417, -58.99011473611232 ],
                    [ -27.455845019204208, -58.99028998828441 ],
                    [ -27.455878514839235, -58.99046524134828 ],
                    [ -27.455977732921237, -58.99063376037627 ],
                    [ -27.456138861394688, -58.99078906913211 ],
                    [ -27.456355708743818, -58.990925198971134 ],
                    [ -27.45661994184369, -58.99103691824481 ],
                    [ -27.45692140616749, -58.99111993338897 ],
                    [ -27.457248516049262, -58.99117105396192 ],
                    [ -27.457588699999995, -58.99118831528412 ],
                    [ -27.45792888395073, -58.99117105396192 ],
                    [ -27.458255993832502, -58.99111993338897 ],
                    [ -27.458557458156303, -58.99103691824481 ],
                    [ -27.458821691256173, -58.990925198971134 ],
                    [ -27.459038538605306, -58.99078906913211 ],
                    [ -27.45919966707875, -58.99063376037627 ],
                    [ -27.459298885160756, -58.99046524134828 ],
                    [ -27.459332380795786, -58.99028998828441 ],
                    [ -27.459298867755823, -58.99011473611232 ],
                    [ -27.459199634918626, -58.98994621962397 ],
                    [ -27.45903849658608, -58.98979091466893 ],
                    [ -27.45882164577489, -58.989654789313285 ],
                    [ -27.458557416137072, -58.98954307452298 ],
                    [ -27.45825596167238, -58.9894600631796 ],
                    [ -27.4579288665458, -58.98940894514629 ],
                    [ -27.457588699999995, -58.98939168471588 ] ] ]
*/

Parameters

• coordinates Array of length 2 or 3 *required
  • First Element: longitude Number *required, can be any number <=180 and >=-180
  • Second Element: latitude Number *required, can be any number <=90 and >=-90
  • Third Element: Ignored if present
• radius Number *required, can be any number >0
• numberOfEdges Number can be any number >=3, defaults to 32 when undefined
• earthRadius Number can be any number >0, defaults to 6378137 (equatorial Earth radius) when undefined

Disclaimers

• Decimal values will not throw error for numberOfEdges! Instead one of the edges of the polygon will be smaller than the others. In other words, all edges will not have the same length if a decimal number is passed as numberOfEdges.
• A circle whoes edge cross longitude edges (-180 or 180) or a latitude edge (-90 or 90) will contain coordinate points that are outside the stanardized coordinates (eg: [182, 23]). This is because there are two ways to represent a line going from [179, x] to [181, y]. One way is simply writing it as [[179, x], [182, y]] while the other is to write it as a multi-polygon. Version <= 2.0.x does only support the first way while release of 2.1.0 will support multi-polygons as well.

Authors

• Gabriel Zimmermann
• Johannes Jarbratt

License

ISC