Function nextPoint

d3-3.2.8/d3.js:2230–2236

(λ, φ)

      sinφ0 = Math.sin(φ);
    };
    function nextPoint(λ, φ) {
      λ *= d3_radians;
      φ = φ * d3_radians / 2 + π / 4;
      var dλ = λ - λ0, cosφ = Math.cos(φ), sinφ = Math.sin(φ), k = sinφ0 * sinφ, u = cosφ0 * cosφ + k * Math.cos(dλ), v = k * Math.sin(dλ);
      d3_geo_areaRingSum.add(Math.atan2(v, u));
      λ0 = λ, cosφ0 = cosφ, sinφ0 = sinφ;
    }
    d3_geo_area.lineEnd = function() {
      nextPoint(λ00, φ00);
    };