// TODO clip input coordinates on opposite hemisphere

d3.geo.azimuthal = function() {

var mode = "orthographic", // or stereographic

origin,

scale = 200,

translate = [480, 250],

x0,

y0,

cy0,

sy0;

function azimuthal(coordinates) {

var x1 = coordinates[0] * d3_radians - x0,

y1 = coordinates[1] * d3_radians,

cx1 = Math.cos(x1),

sx1 = Math.sin(x1),

cy1 = Math.cos(y1),

sy1 = Math.sin(y1),

k = mode == "stereographic" ? 1 / (1 + sy0 * sy1 + cy0 * cy1 * cx1) : 1,

x = k * cy1 * sx1,

y = k * (sy0 * cy1 * cx1 - cy0 * sy1);

return [

scale * x + translate[0],

scale * y + translate[1]

];

}

azimuthal.mode = function(x) {

if (!arguments.length) return mode;

mode = x;

return azimuthal;

};

azimuthal.origin = function(x) {

if (!arguments.length) return origin;

origin = x;

x0 = origin[0] * d3_radians;

y0 = origin[1] * d3_radians;

cy0 = Math.cos(y0);

sy0 = Math.sin(y0);

return azimuthal;

};

azimuthal.scale = function(x) {

if (!arguments.length) return scale;

scale = +x;

return azimuthal;

};

azimuthal.translate = function(x) {

if (!arguments.length) return translate;

translate = [+x[0], +x[1]];

return azimuthal;

};

return azimuthal.origin([0, 0]);

};