node_modules/@turf/area/dist/js/index.js

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
var meta_1 = require("@turf/meta");
// Note: change RADIUS => earthRadius
var RADIUS = 6378137;
/**
 * Takes one or more features and returns their area in square meters.
 *
 * @name area
 * @param {GeoJSON} geojson input GeoJSON feature(s)
 * @returns {number} area in square meters
 * @example
 * var polygon = turf.polygon([[[125, -15], [113, -22], [154, -27], [144, -15], [125, -15]]]);
 *
 * var area = turf.area(polygon);
 *
 * //addToMap
 * var addToMap = [polygon]
 * polygon.properties.area = area
 */
function area(geojson) {
    return meta_1.geomReduce(geojson, function (value, geom) {
        return value + calculateArea(geom);
    }, 0);
}
exports.default = area;
/**
 * Calculate Area
 *
 * @private
 * @param {Geometry} geom GeoJSON Geometries
 * @returns {number} area
 */
function calculateArea(geom) {
    var total = 0;
    var i;
    switch (geom.type) {
        case "Polygon":
            return polygonArea(geom.coordinates);
        case "MultiPolygon":
            for (i = 0; i < geom.coordinates.length; i++) {
                total += polygonArea(geom.coordinates[i]);
            }
            return total;
        case "Point":
        case "MultiPoint":
        case "LineString":
        case "MultiLineString":
            return 0;
    }
    return 0;
}
function polygonArea(coords) {
    var total = 0;
    if (coords && coords.length > 0) {
        total += Math.abs(ringArea(coords[0]));
        for (var i = 1; i < coords.length; i++) {
            total -= Math.abs(ringArea(coords[i]));
        }
    }
    return total;
}
/**
 * @private
 * Calculate the approximate area of the polygon were it projected onto the earth.
 * Note that this area will be positive if ring is oriented clockwise, otherwise it will be negative.
 *
 * Reference:
 * Robert. G. Chamberlain and William H. Duquette, "Some Algorithms for Polygons on a Sphere",
 * JPL Publication 07-03, Jet Propulsion
 * Laboratory, Pasadena, CA, June 2007 https://trs.jpl.nasa.gov/handle/2014/40409
 *
 * @param {Array<Array<number>>} coords Ring Coordinates
 * @returns {number} The approximate signed geodesic area of the polygon in square meters.
 */
function ringArea(coords) {
    var p1;
    var p2;
    var p3;
    var lowerIndex;
    var middleIndex;
    var upperIndex;
    var i;
    var total = 0;
    var coordsLength = coords.length;
    if (coordsLength > 2) {
        for (i = 0; i < coordsLength; i++) {
            if (i === coordsLength - 2) {
                // i = N-2
                lowerIndex = coordsLength - 2;
                middleIndex = coordsLength - 1;
                upperIndex = 0;
            }
            else if (i === coordsLength - 1) {
                // i = N-1
                lowerIndex = coordsLength - 1;
                middleIndex = 0;
                upperIndex = 1;
            }
            else {
                // i = 0 to N-3
                lowerIndex = i;
                middleIndex = i + 1;
                upperIndex = i + 2;
            }
            p1 = coords[lowerIndex];
            p2 = coords[middleIndex];
            p3 = coords[upperIndex];
            total += (rad(p3[0]) - rad(p1[0])) * Math.sin(rad(p2[1]));
        }
        total = (total * RADIUS * RADIUS) / 2;
    }
    return total;
}
function rad(num) {
    return (num * Math.PI) / 180;
}