Function areaPoint

docs/app/js/sanddance-app.js:131905–131915

(lambda, phi)

    lambda0 = lambda, cosPhi0 = (0, _mathJs.cos)(phi = phi / 2 + (0, _mathJs.quarterPi)), sinPhi0 = (0, _mathJs.sin)(phi);
}
function areaPoint(lambda, phi) {
    lambda *= (0, _mathJs.radians), phi *= (0, _mathJs.radians);
    phi = phi / 2 + (0, _mathJs.quarterPi); // half the angular distance from south pole
    // Spherical excess E for a spherical triangle with vertices: south pole,
    // previous point, current point.  Uses a formula derived from Cagnoli’s
    // theorem.  See Todhunter, Spherical Trig. (1871), Sec. 103, Eq. (2).
    var dLambda = lambda - lambda0, sdLambda = dLambda >= 0 ? 1 : -1, adLambda = sdLambda * dLambda, cosPhi = (0, _mathJs.cos)(phi), sinPhi = (0, _mathJs.sin)(phi), k = sinPhi0 * sinPhi, u = cosPhi0 * cosPhi + k * (0, _mathJs.cos)(adLambda), v = k * sdLambda * (0, _mathJs.sin)(adLambda);
    areaRingSum.add((0, _mathJs.atan2)(v, u));
    // Advance the previous points.
    lambda0 = lambda, cosPhi0 = cosPhi, sinPhi0 = sinPhi;
}
exports.default = function(object) {
    areaSum = new (0, _d3Array.Adder)();
    (0, _streamJsDefault.default)(object, areaStream);