covutils/lib/domain/polygon.js

Utilities for creating, transforming, and handling Coverage Data objects.

'use strict';

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

var _pointInBigPolygon = require('point-in-big-polygon');

var _pointInBigPolygon2 = _interopRequireDefault(_pointInBigPolygon);

var _spherical = require('topojson/lib/topojson/spherical.js');

var _cartesian = require('topojson/lib/topojson/cartesian.js');

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

/**
 * Modifies the point order of the given polygon rings such that the first ring is ordered
 * clockwise and all others anti-clockwise. Modification happens in-place.
 *
 * @param {Array} rings - Polygon rings to reorder (in-place)
 * @param {boolean} [isCartesian=false] - whether coordinates are cartesian or spherical degrees
 */
function ensureClockwisePolygon(rings) {
  var isCartesian = arguments.length <= 1 || arguments[1] === undefined ? false : arguments[1];

  // first ring = exterior, clockwise
  // other rings = interior, anti-clockwise
  var ringAreaFn = isCartesian ? _cartesian.ringArea : _spherical.ringArea;
  for (var i = 0; i < rings.length; i++) {
    var area = ringAreaFn(rings[i]);
    if (i === 0 && area < 0 || i > 0 && area > 0) {
      rings[i].reverse();
    }
  }
}

/**
 * Preprocesses an array of polygons to answer the point-in-polygon question efficiently.
 *
 * @param {Array} polygons - A list of polygons where the exterior ring of each polygon is in clockwise and the interior rings in anti-clockwise order.
 * @return {function} A function classify(point) which returns the index of the first found polygon containing point, or -1 if not in any polygon.
 */
function getPointInPolygonsFn(polygons) {
  var classifiers = polygons.map(_pointInBigPolygon2.default);
  var npolys = polygons.length;

  return function (point) {
    for (var i = 0; i < npolys; i++) {
      if (classifiers[i](point) <= 0) {
        return i;
      }
    }
    return -1;
  };
}