keplerjs/Core/body2latlong.js

Kepler solver to compute a celestial body position over the surface of the earth.

const { norm, subtract } = require("mathjs");
const { keplerslv } = require("./keplerslv");
const { obtelements } = require("./obtelements");
const { r2longlat } = require("./r2longlat");
const { statevector } = require("./statevector");
const { trueanom } = require("./trueanom");


exports.body2latlong = (body) => {

    // Standard gravitational parameter of the sun
    const mu = 1.32712440018e11; // [km ^ 3 s ^ -2]

    // Earth object 
    // for the simiplicity of the constant we have supposed 
    // the orbital parameters of the earth to be the ones in 0 JD

    const earth = {
        a: 1, // UA
        e: 0.01671022, //deg
        i: 0.00005,//deg
        om: 0,//deg
        w: -11.26064, //deg
        ma: 100.46435 - (-11.26064),//deg
    }
    
    // Orbital elements of the body and the earth
    const obt_body = obtelements(body);
    const obt_e = obtelements(earth);

    // Solving keplers equation
    const E_e = keplerslv(obt_e);
    const E_body = keplerslv(obt_body);


    // True anomaly [rad]
    const theta_e = trueanom(obt_e, E_e);
    const theta_body = trueanom(obt_body, E_body);


    // Angular momentum
    const rv_body = statevector(obt_body, theta_body, mu);
    const rv_e = statevector(obt_e, theta_e, mu);

    const rv = subtract(rv_body.r, rv_e.r);
    const r_ = norm(rv);


    // Finally compute the longitude and latitude
    const pos = r2longlat(rv, r_);
    
    return pos;
}