s2-tools/dist/proj4/constants/derives.js

A collection of geospatial tools primarily designed for WGS84, Web Mercator, and S2.

import { ellipsoids } from './ellipsoid';
import { EPSLN, RA4, RA6, SIXTH } from './values';
/**
 * Derives an ellipsoid's eccentricity for an object
 * @param el - ellipsoid object to modify
 */
export function deriveEccentricity(el) {
    let a = el.a ?? 0;
    const b = el.b ?? 0;
    let a2 = a * a; // used in geocentric
    const b2 = b * b; // used in geocentric
    let es = (a2 - b2) / a2; // e ^ 2
    let e = 0;
    if (el.rA === true) {
        a *= 1 - es * (SIXTH + es * (RA4 + es * RA6));
        a2 = a * a;
        es = 0;
    }
    else {
        e = Math.sqrt(es); // eccentricity
    }
    const ep2 = (a2 - b2) / b2; // used in geocentric
    el.es = es;
    el.e = e;
    el.ep2 = ep2;
}
/**
 * Builds a sphere with ellipsoid parameters
 * @param obj - an object with/wihtout sphere properties and builds the sphere
 */
export function deriveSphere(obj) {
    if (obj.a === undefined) {
        // do we have an ellipsoid?
        let ellipse = match(ellipsoids, obj.ellps);
        if (ellipse === undefined)
            ellipse = ellipsoids.WGS84;
        obj.a = ellipse.a;
        obj.b = ellipse.b;
        obj.rf = ellipse.rf;
    }
    if (obj.rf !== undefined && obj.b === undefined) {
        obj.b = (1.0 - 1.0 / obj.rf) * obj.a;
    }
    if (obj.rf === undefined && obj.b !== undefined) {
        obj.rf = (obj.a - obj.b) / obj.a;
    }
    if (obj.rf === 0 || (obj.b !== undefined && Math.abs(obj.a - obj.b) < EPSLN)) {
        obj.sphere = true;
        obj.b = obj.a;
    }
}
/**
 * @param obj - the object to search
 * @param key - the key to search with
 * @returns - the value of the key
 */
function match(obj, key) {
    if (key === undefined)
        return;
    if (obj[key] !== undefined)
        return obj[key];
}
//# sourceMappingURL=derives.js.map