Function forward

d3-3.2.8/d3.js:3073–3076

(λ, φ)

  function d3_geo_conicEqualArea(φ0, φ1) {
    var sinφ0 = Math.sin(φ0), n = (sinφ0 + Math.sin(φ1)) / 2, C = 1 + sinφ0 * (2 * n - sinφ0), ρ0 = Math.sqrt(C) / n;
    function forward(λ, φ) {
      var ρ = Math.sqrt(C - 2 * n * Math.sin(φ)) / n;
      return [ ρ * Math.sin(λ *= n), ρ0 - ρ * Math.cos(λ) ];
    }
    forward.invert = function(x, y) {
      var ρ0_y = ρ0 - y;
      return [ Math.atan2(x, ρ0_y) / n, d3_asin((C - (x * x + ρ0_y * ρ0_y) * n * n) / (2 * n)) ];