code: function bonne(coordinates) {
      var x = coordinates[0] * d3_geo_radians - x0,
          y = coordinates[1] * d3_geo_radians - y0;
      if (y1) {
        var p = c1 + y1 - y, E = x * Math.cos(y) / p;
        x = p * Math.sin(E);
        y = p * Math.cos(E) - c1;
      } else {
        x *= Math.cos(y);
        y *= -1;
      }
      return [
        scale * x + translate[0],
        scale * y + translate[1]
      ];
    }
docs: cot(y1)