d3-geo-projection/src/mollweide.js

Extended geographic projections for d3-geo.

import {geoProjection as projection} from "d3-geo";
import {abs, asin, cos, epsilon, halfPi, pi, sin, sqrt2} from "./math.js";

export function mollweideBromleyTheta(cp, phi) {
  var cpsinPhi = cp * sin(phi), i = 30, delta;
  do phi -= delta = (phi + sin(phi) - cpsinPhi) / (1 + cos(phi));
  while (abs(delta) > epsilon && --i > 0);
  return phi / 2;
}

export function mollweideBromleyRaw(cx, cy, cp) {

  function forward(lambda, phi) {
    return [cx * lambda * cos(phi = mollweideBromleyTheta(cp, phi)), cy * sin(phi)];
  }

  forward.invert = function(x, y) {
    return y = asin(y / cy), [x / (cx * cos(y)), asin((2 * y + sin(2 * y)) / cp)];
  };

  return forward;
}

export var mollweideRaw = mollweideBromleyRaw(sqrt2 / halfPi, sqrt2, pi);

export default function() {
  return projection(mollweideRaw)
      .scale(169.529);
}