package.es-modules.Maps.Projections.EqualEarth.js Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of highcharts Show documentation
JavaScript charting framework
The newest version!
/* *
 *
 * Equal Earth projection, an equal-area projection designed to minimize
 * distortion and remain pleasing to the eye.
 *
 * Invented by Bojan Šavrič, Bernhard Jenny, and Tom Patterson in 2018. It is
 * inspired by the widely used Robinson projection.
 *
 * */
'use strict';
/* *
 *
 *  Constants
 *
 * */
const A1 = 1.340264, A2 = -0.081106, A3 = 0.000893, A4 = 0.003796, M = Math.sqrt(3) / 2.0, scale = 74.03120656864502;
/* *
 *
 *  Class
 *
 * */
class EqualEarth {
    constructor() {
        /* *
         *
         *  Properties
         *
         * */
        this.bounds = {
            x1: -200.37508342789243,
            x2: 200.37508342789243,
            y1: -97.52595454902263,
            y2: 97.52595454902263
        };
    }
    /* *
     *
     *  Functions
     *
     * */
    forward(lonLat) {
        const d = Math.PI / 180, paramLat = Math.asin(M * Math.sin(lonLat[1] * d)), paramLatSq = paramLat * paramLat, paramLatPow6 = paramLatSq * paramLatSq * paramLatSq;
        const x = lonLat[0] * d * Math.cos(paramLat) * scale /
            (M * (A1 +
                3 * A2 * paramLatSq +
                paramLatPow6 * (7 * A3 + 9 * A4 * paramLatSq))), y = paramLat * scale * (A1 + A2 * paramLatSq + paramLatPow6 * (A3 + A4 * paramLatSq));
        return [x, y];
    }
    inverse(xy) {
        const x = xy[0] / scale, y = xy[1] / scale, d = 180 / Math.PI, epsilon = 1e-9;
        let paramLat = y, paramLatSq, paramLatPow6, fy, fpy, dlat;
        for (let i = 0; i < 12; ++i) {
            paramLatSq = paramLat * paramLat;
            paramLatPow6 = paramLatSq * paramLatSq * paramLatSq;
            fy = paramLat * (A1 + A2 * paramLatSq + paramLatPow6 * (A3 + A4 * paramLatSq)) - y;
            fpy = A1 + 3 * A2 * paramLatSq + paramLatPow6 * (7 * A3 + 9 * A4 * paramLatSq);
            paramLat -= dlat = fy / fpy;
            if (Math.abs(dlat) < epsilon) {
                break;
            }
        }
        paramLatSq = paramLat * paramLat;
        paramLatPow6 = paramLatSq * paramLatSq * paramLatSq;
        const lon = d * M * x * (A1 + 3 * A2 * paramLatSq + paramLatPow6 *
            (7 * A3 + 9 * A4 * paramLatSq)) / Math.cos(paramLat), lat = d * Math.asin(Math.sin(paramLat) / M);
        // If lons are beyond the border of a map -> resolve via break
        if (Math.abs(lon) > 180) {
            return [NaN, NaN];
        }
        return [lon, lat];
    }
}
/* *
 *
 *  Default Export
 *
 * */
export default EqualEarth;