@visx/vendor/vendor-cjs/d3-geo/src/area.js

vendored packages for visx

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.areaStream = exports.areaRingSum = void 0;
exports.default = _default;
var _index = require("../../../vendor-cjs/d3-array/src/index.js");
var _math = require("./math.js");
var _noop = _interopRequireDefault(require("./noop.js"));
var _stream = _interopRequireDefault(require("./stream.js"));
function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }
var areaRingSum = new _index.Adder();

// hello?
exports.areaRingSum = areaRingSum;
var areaSum = new _index.Adder(),
  lambda00,
  phi00,
  lambda0,
  cosPhi0,
  sinPhi0;
var areaStream = {
  point: _noop.default,
  lineStart: _noop.default,
  lineEnd: _noop.default,
  polygonStart: function () {
    exports.areaRingSum = areaRingSum = new _index.Adder();
    areaStream.lineStart = areaRingStart;
    areaStream.lineEnd = areaRingEnd;
  },
  polygonEnd: function () {
    var areaRing = +areaRingSum;
    areaSum.add(areaRing < 0 ? _math.tau + areaRing : areaRing);
    this.lineStart = this.lineEnd = this.point = _noop.default;
  },
  sphere: function () {
    areaSum.add(_math.tau);
  }
};
exports.areaStream = areaStream;
function areaRingStart() {
  areaStream.point = areaPointFirst;
}
function areaRingEnd() {
  areaPoint(lambda00, phi00);
}
function areaPointFirst(lambda, phi) {
  areaStream.point = areaPoint;
  lambda00 = lambda, phi00 = phi;
  lambda *= _math.radians, phi *= _math.radians;
  lambda0 = lambda, cosPhi0 = (0, _math.cos)(phi = phi / 2 + _math.quarterPi), sinPhi0 = (0, _math.sin)(phi);
}
function areaPoint(lambda, phi) {
  lambda *= _math.radians, phi *= _math.radians;
  phi = phi / 2 + _math.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, _math.cos)(phi),
    sinPhi = (0, _math.sin)(phi),
    k = sinPhi0 * sinPhi,
    u = cosPhi0 * cosPhi + k * (0, _math.cos)(adLambda),
    v = k * sdLambda * (0, _math.sin)(adLambda);
  areaRingSum.add((0, _math.atan2)(v, u));

  // Advance the previous points.
  lambda0 = lambda, cosPhi0 = cosPhi, sinPhi0 = sinPhi;
}
function _default(object) {
  areaSum = new _index.Adder();
  (0, _stream.default)(object, areaStream);
  return areaSum * 2;
}