text: import {geoProjection as projection} from "d3-geo";
  import {abs, asin, cos, epsilon, halfPi, pi, sin, sqrt} from "./math";
  
  export function mtFlatPolarSinusoidalRaw(lambda, phi) {
    var A = sqrt(6 / (4 + pi)),
        k = (1 + pi / 4) * sin(phi),
        theta = phi / 2;
    for (var i = 0, delta; i < 25; i++) {
      theta -= delta = (theta / 2 + sin(theta) - k) / (0.5 + cos(theta));
      if (abs(delta) < epsilon) break;
    }
    return [
      A * (0.5 + cos(theta)) * lambda / 1.5,
      A * theta
    ];
  }
  
  mtFlatPolarSinusoidalRaw.invert = function(x, y) {
    var A = sqrt(6 / (4 + pi)),
        theta = y / A;
    if (abs(abs(theta) - halfPi) < epsilon) theta = theta < 0 ? -halfPi : halfPi;
    return [
      1.5 * x / (A * (0.5 + cos(theta))),
      asin((theta / 2 + sin(theta)) / (1 + pi / 4))
    ];
  };
  
  export default function() {
    return projection(mtFlatPolarSinusoidalRaw)
        .scale(166.518);
  }
  