make-geo-json/dist/makeCircle.js

Converts polylines, wkts, wkbs, polygons, circles, rectangles, as well as standard geoJSON into geoJSON MultiPolygon Feature Objects. Converts wkb_list and FeatureCollection to arrays.

'use strict';

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.default = generateCircleApprox;

var _mathjs = require('mathjs');

var _mathjs2 = _interopRequireDefault(_mathjs);

var _map = require('lodash/map');

var _map2 = _interopRequireDefault(_map);

var _range = require('lodash/range');

var _range2 = _interopRequireDefault(_range);

var _reverse = require('lodash/reverse');

var _reverse2 = _interopRequireDefault(_reverse);

function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }

// convert degrees (lat/long) to radians
// MAKE A CIRCLE
// Using Doc's code
// https://gist.github.com/otherchris/c529f2f39fd9af273455933eb3a50e90
// generateCircleApprox()
const radians = deg => deg / 360 * 2 * Math.PI;

// create a set of points around the origin at the given radius
// 24 is usually a good number of sides, consider hard coding that
const rotatedPointsOrigin = (radius, sides) => {
  const z = new _mathjs2.default.complex({ phi: 0, r: radius });
  const angle = 2 * Math.PI / sides;
  return (0, _map2.default)((0, _range2.default)(sides), x => {
    const i = _mathjs2.default.complex(0, 1);
    const point = _mathjs2.default.multiply(z, _mathjs2.default.exp(_mathjs2.default.multiply(x, angle, _mathjs2.default.complex(0, 1))));
    return [_mathjs2.default.re(point), _mathjs2.default.im(point)];
  });
};

// scale points to coordinate system
// const latFactor = 69.172 // if miles
const latFactor = 111321.543; // if meters
const scalePoints = (points, lat) => {
  const lngFactor = _mathjs2.default.cos(radians(lat)) * latFactor;
  return (0, _map2.default)(points, x => [x[0] / lngFactor, x[1] / latFactor]);
};

// move this circle to the correct place on the map
const translatePoints = (points, center) => (0, _map2.default)(points, point => [point[0] + center[0], point[1] + center[1]]);

// create GeoJSON feature from circle
// (using a 24 sided approximation by default)
function generateCircleApprox(radius, center, sides = 24) {
  const points = rotatedPointsOrigin(radius, sides);
  const scaledPoints = scalePoints(points, center[0]);
  const translatedPoints = translatePoints(scaledPoints, center);
  return translatedPoints;
  /* const reversedPoints = map(translatedPoints, (x) => reverse(x));
   * return reversedPoints; */
  /* return {
   *   type: 'Feature',
   *   properties: {
   *     radius,
   *     center,
   *     sides,
   *   },
   *   geometry: {
   *     type: 'MultiPolygon',
   *     coordinates: [[reversedPoints]],
   *   },
   * }; */
}