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(function(){d3.geo = {};
var d3_geo_radians = Math.PI / 180;
// TODO clip input coordinates on opposite hemisphere
d3.geo.azimuthal = function() {
var mode = "orthographic", // or stereographic, gnomonic, equidistant or equalarea
origin,
scale = 200,
translate = [480, 250],
x0,
y0,
cy0,
sy0;
function azimuthal(coordinates) {
var x1 = coordinates[0] * d3_geo_radians - x0,
y1 = coordinates[1] * d3_geo_radians,
cx1 = Math.cos(x1),
sx1 = Math.sin(x1),
cy1 = Math.cos(y1),
sy1 = Math.sin(y1),
cc = mode !== "orthographic" ? sy0 * sy1 + cy0 * cy1 * cx1 : null,
c,
k = mode === "stereographic" ? 1 / (1 + cc)
: mode === "gnomonic" ? 1 / cc
: mode === "equidistant" ? (c = Math.acos(cc), c ? c / Math.sin(c) : 0)
: mode === "equalarea" ? Math.sqrt(2 / (1 + cc))
: 1,
x = k * cy1 * sx1,
y = k * (sy0 * cy1 * cx1 - cy0 * sy1);
return [
scale * x + translate[0],
scale * y + translate[1]
];
}
azimuthal.invert = function(coordinates) {
var x = (coordinates[0] - translate[0]) / scale,
y = (coordinates[1] - translate[1]) / scale,
p = Math.sqrt(x * x + y * y),
c = mode === "stereographic" ? 2 * Math.atan(p)
: mode === "gnomonic" ? Math.atan(p)
: mode === "equidistant" ? p
: mode === "equalarea" ? 2 * Math.asin(.5 * p)
: Math.asin(p),
sc = Math.sin(c),
cc = Math.cos(c);
return [
(x0 + Math.atan2(x * sc, p * cy0 * cc + y * sy0 * sc)) / d3_geo_radians,
Math.asin(cc * sy0 - (p ? (y * sc * cy0) / p : 0)) / d3_geo_radians
];
};
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_geo_radians;
y0 = origin[1] * d3_geo_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]);
};
// Derived from Tom Carden's Albers implementation for Protovis.
// http://gist.github.com/476238
// http://mathworld.wolfram.com/AlbersEqual-AreaConicProjection.html
d3.geo.albers = function() {
var origin = [-98, 38],
parallels = [29.5, 45.5],
scale = 1000,
translate = [480, 250],
lng0, // d3_geo_radians * origin[0]
n,
C,
p0;
function albers(coordinates) {
var t = n * (d3_geo_radians * coordinates[0] - lng0),
p = Math.sqrt(C - 2 * n * Math.sin(d3_geo_radians * coordinates[1])) / n;
return [
scale * p * Math.sin(t) + translate[0],
scale * (p * Math.cos(t) - p0) + translate[1]
];
}
albers.invert = function(coordinates) {
var x = (coordinates[0] - translate[0]) / scale,
y = (coordinates[1] - translate[1]) / scale,
p0y = p0 + y,
t = Math.atan2(x, p0y),
p = Math.sqrt(x * x + p0y * p0y);
return [
(lng0 + t / n) / d3_geo_radians,
Math.asin((C - p * p * n * n) / (2 * n)) / d3_geo_radians
];
};
function reload() {
var phi1 = d3_geo_radians * parallels[0],
phi2 = d3_geo_radians * parallels[1],
lat0 = d3_geo_radians * origin[1],
s = Math.sin(phi1),
c = Math.cos(phi1);
lng0 = d3_geo_radians * origin[0];
n = .5 * (s + Math.sin(phi2));
C = c * c + 2 * n * s;
p0 = Math.sqrt(C - 2 * n * Math.sin(lat0)) / n;
return albers;
}
albers.origin = function(x) {
if (!arguments.length) return origin;
origin = [+x[0], +x[1]];
return reload();
};
albers.parallels = function(x) {
if (!arguments.length) return parallels;
parallels = [+x[0], +x[1]];
return reload();
};
albers.scale = function(x) {
if (!arguments.length) return scale;
scale = +x;
return albers;
};
albers.translate = function(x) {
if (!arguments.length) return translate;
translate = [+x[0], +x[1]];
return albers;
};
return reload();
};
// A composite projection for the United States, 960x500. The set of standard
// parallels for each region comes from USGS, which is published here:
// http://egsc.usgs.gov/isb/pubs/MapProjections/projections.html#albers
// TODO allow the composite projection to be rescaled?
d3.geo.albersUsa = function() {
var lower48 = d3.geo.albers();
var alaska = d3.geo.albers()
.origin([-160, 60])
.parallels([55, 65]);
var hawaii = d3.geo.albers()
.origin([-160, 20])
.parallels([8, 18]);
var puertoRico = d3.geo.albers()
.origin([-60, 10])
.parallels([8, 18]);
function albersUsa(coordinates) {
var lon = coordinates[0],
lat = coordinates[1];
return (lat > 50 ? alaska
: lon < -140 ? hawaii
: lat < 21 ? puertoRico
: lower48)(coordinates);
}
albersUsa.scale = function(x) {
if (!arguments.length) return lower48.scale();
lower48.scale(x);
alaska.scale(x * .6);
hawaii.scale(x);
puertoRico.scale(x * 1.5);
return albersUsa.translate(lower48.translate());
};
albersUsa.translate = function(x) {
if (!arguments.length) return lower48.translate();
var dz = lower48.scale() / 1000,
dx = x[0],
dy = x[1];
lower48.translate(x);
alaska.translate([dx - 400 * dz, dy + 170 * dz]);
hawaii.translate([dx - 190 * dz, dy + 200 * dz]);
puertoRico.translate([dx + 580 * dz, dy + 430 * dz]);
return albersUsa;
};
return albersUsa.scale(lower48.scale());
};
d3.geo.bonne = function() {
var scale = 200,
translate = [480, 250],
x0, // origin longitude in radians
y0, // origin latitude in radians
y1, // parallel latitude in radians
c1; // cot(y1)
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]
];
}
bonne.invert = function(coordinates) {
var x = (coordinates[0] - translate[0]) / scale,
y = (coordinates[1] - translate[1]) / scale;
if (y1) {
var c = c1 + y, p = Math.sqrt(x * x + c * c);
y = c1 + y1 - p;
x = x0 + p * Math.atan2(x, c) / Math.cos(y);
} else {
y *= -1;
x /= Math.cos(y);
}
return [
x / d3_geo_radians,
y / d3_geo_radians
];
};
// 90° for Werner, 0° for Sinusoidal
bonne.parallel = function(x) {
if (!arguments.length) return y1 / d3_geo_radians;
c1 = 1 / Math.tan(y1 = x * d3_geo_radians);
return bonne;
};
bonne.origin = function(x) {
if (!arguments.length) return [x0 / d3_geo_radians, y0 / d3_geo_radians];
x0 = x[0] * d3_geo_radians;
y0 = x[1] * d3_geo_radians;
return bonne;
};
bonne.scale = function(x) {
if (!arguments.length) return scale;
scale = +x;
return bonne;
};
bonne.translate = function(x) {
if (!arguments.length) return translate;
translate = [+x[0], +x[1]];
return bonne;
};
return bonne.origin([0, 0]).parallel(45);
};
d3.geo.equirectangular = function() {
var scale = 500,
translate = [480, 250];
function equirectangular(coordinates) {
var x = coordinates[0] / 360,
y = -coordinates[1] / 360;
return [
scale * x + translate[0],
scale * y + translate[1]
];
}
equirectangular.invert = function(coordinates) {
var x = (coordinates[0] - translate[0]) / scale,
y = (coordinates[1] - translate[1]) / scale;
return [
360 * x,
-360 * y
];
};
equirectangular.scale = function(x) {
if (!arguments.length) return scale;
scale = +x;
return equirectangular;
};
equirectangular.translate = function(x) {
if
8000
(!arguments.length) return translate;
translate = [+x[0], +x[1]];
return equirectangular;
};
return equirectangular;
};
d3.geo.mercator = function() {
var scale = 500,
translate = [480, 250];
function mercator(coordinates) {
var x = coordinates[0] / 360,
y = -(Math.log(Math.tan(Math.PI / 4 + coordinates[1] * d3_geo_radians / 2)) / d3_geo_radians) / 360;
return [
scale * x + translate[0],
scale * Math.max(-.5, Math.min(.5, y)) + translate[1]
];
}
mercator.invert = function(coordinates) {
var x = (coordinates[0] - translate[0]) / scale,
y = (coordinates[1] - translate[1]) / scale;
return [
360 * x,
2 * Math.atan(Math.exp(-360 * y * d3_geo_radians)) / d3_geo_radians - 90
];
};
mercator.scale = function(x) {
if (!arguments.length) return scale;
scale = +x;
return mercator;
};
mercator.translate = function(x) {
if (!arguments.length) return translate;
translate = [+x[0], +x[1]];
return mercator;
};
return mercator;
};
function d3_geo_type(types, defaultValue) {
return function(object) {
return object && object.type in types ? types[object.type](object) : defaultValue;
};
}
/**
* Returns a function that, given a GeoJSON object (e.g., a feature), returns
* the corresponding SVG path. The function can be customized by overriding the
* projection. Point features are mapped to circles with a default radius of
* 4.5px; the radius can be specified either as a constant or a function that
* is evaluated per object.
*/
d3.geo.path = function() {
var pointRadius = 4.5,
pointCircle = d3_path_circle(pointRadius),
projection = d3.geo.albersUsa();
function path(d, i) {
if (typeof pointRadius === "function") {
pointCircle = d3_path_circle(pointRadius.apply(this, arguments));
}
return pathType(d) || null;
}
function project(coordinates) {
return projection(coordinates).join(",");
}
var pathType = d3_geo_type({
FeatureCollection: function(o) {
var path = [],
features = o.features,
i = -1, // features.index
n = features.length;
while (++i < n) path.push(pathType(features[i].geometry));
return path.join("");
},
Feature: function(o) {
return pathType(o.geometry);
},
Point: function(o) {
return "M" + project(o.coordinates) + pointCircle;
},
MultiPoint: function(o) {
var path = [],
coordinates = o.coordinates,
i = -1, // coordinates.index
n = coordinates.length;
while (++i < n) path.push("M", project(coordinates[i]), pointCircle);
return path.join("");
},
LineString: function(o) {
var path = ["M"],
coordinates = o.coordinates,
i = -1, // coordinates.index
n = coordinates.length;
while (++i < n) path.push(project(coordinates[i]), "L");
path.pop();
return path.join("");
},
MultiLineString: function(o) {
var path = [],
coordinates = o.coordinates,
i = -1, // coordinates.index
n = coordinates.length,
subcoordinates, // coordinates[i]
j, // subcoordinates.index
m; // subcoordinates.length
while (++i < n) {
subcoordinates = coordinates[i];
j = -1;
m = subcoordinates.length;
path.push("M");
while (++j < m) path.push(project(subcoordinates[j]), "L");
path.pop();
}
return path.join("");
},
Polygon: function(o) {
var path = [],
coordinates = o.coordinates,
i = -1, // coordinates.index
n = coordinates.length,
subcoordinates, // coordinates[i]
j, // subcoordinates.index
m; // subcoordinates.length
while (++i < n) {
subcoordinates = coordinates[i];
j = -1;
if ((m = subcoordinates.length - 1) > 0) {
path.push("M");
while (++j < m) path.push(project(subcoordinates[j]), "L");
path[path.length - 1] = "Z";
}
}
return path.join("");
},
MultiPolygon: function(o) {
var path = [],
coordinates = o.coordinates,
i = -1, // coordinates index
n = coordinates.length,
subcoordinates, // coordinates[i]
j, // subcoordinates index
m, // subcoordinates.length
subsubcoordinates, // subcoordinates[j]
k, // subsubcoordinates index
p; // subsubcoordinates.length
while (++i < n) {
subcoordinates = coordinates[i];
j = -1;
m = subcoordinates.length;
while (++j < m) {
subsubcoordinates = subcoordinates[j];
k = -1;
if ((p = subsubcoordinates.length - 1) > 0) {
path.push("M");
while (++k < p) path.push(project(subsubcoordinates[k]), "L");
path[path.length - 1] = "Z";
}
}
}
return path.join("");
},
GeometryCollection: function(o) {
var path = [],
geometries = o.geometries,
i = -1, // geometries index
n = geometries.length;
while (++i < n) path.push(pathType(geometries[i]));
return path.join("");
}
});
var areaType = path.area = d3_geo_type({
FeatureCollection: function(o) {
var area = 0,
features = o.features,
i = -1, // features.index
n = features.length;
while (++i < n) area += areaType(features[i]);
return area;
},
Feature: function(o) {
return areaType(o.geometry);
},
Polygon: function(o) {
return polygonArea(o.coordinates);
},
MultiPolygon: function(o) {
var sum = 0,
coordinates = o.coordinates,
i = -1, // coordinates index
n = coordinates.length;
while (++i < n) sum += polygonArea(coordinates[i]);
return sum;
},
GeometryCollection: function(o) {
var sum = 0,
geometries = o.geometries,
i = -1, // geometries index
n = geometries.length;
while (++i < n) sum += areaType(geometries[i]);
return sum;
}
}, 0);
function polygonArea(coordinates) {
var sum = area(coordinates[0]), // exterior ring
i = 0, // coordinates.index
n = coordinates.length;
while (++i < n) sum -= area(coordinates[i]); // holes
return sum;
}
function polygonCentroid(coordinates) {
var polygon = d3.geom.polygon(coordinates[0].map(projection)), // exterior ring
area = polygon.area(),
centroid = polygon.centroid(area < 0 ? (area *= -1, 1) : -1),
x = centroid[0],
y = centroid[1],
z = area,
i = 0, // coordinates index
n = coordinates.length;
while (++i < n) {
polygon = d3.geom.polygon(coordinates[i].map(projection)); // holes
area = polygon.area();
centroid = polygon.centroid(area < 0 ? (area *= -1, 1) : -1);
x -= centroid[0];
y -= centroid[1];
z -= area;
}
return [x, y, 6 * z]; // weighted centroid
}
var centroidType = path.centroid = d3_geo_type({
// TODO FeatureCollection
// TODO Point
// TODO MultiPoint
// TODO LineString
// TODO MultiLineString
// TODO GeometryCollection
Feature: function(o) {
return centroidType(o.geometry);
},
Polygon: function(o) {
var centroid = polygonCentroid(o.coordinates);
return [centroid[0] / centroid[2], centroid[1] / centroid[2]];
},
MultiPolygon: function(o) {
var area = 0,<
10000
/div>
coordinates = o.coordinates,
centroid,
x = 0,
y = 0,
z = 0,
i = -1, // coordinates index
n = coordinates.length;
while (++i < n) {
centroid = polygonCentroid(coordinates[i]);
x += centroid[0];
y += centroid[1];
z += centroid[2];
}
return [x / z, y / z];
}
});
function area(coordinates) {
return Math.abs(d3.geom.polygon(coordinates.map(projection)).area());
}
path.projection = function(x) {
projection = x;
return path;
};
path.pointRadius = function(x) {
if (typeof x === "function") pointRadius = x;
else {
pointRadius = +x;
pointCircle = d3_path_circle(pointRadius);
}
return path;
};
return path;
};
function d3_path_circle(radius) {
return "m0," + radius
+ "a" + radius + "," + radius + " 0 1,1 0," + (-2 * radius)
+ "a" + radius + "," + radius + " 0 1,1 0," + (+2 * radius)
+ "z";
}
/**
* Given a GeoJSON object, returns the corresponding bounding box. The bounding
* box is represented by a two-dimensional array: [[left, bottom], [right,
* top]], where left is the minimum longitude, bottom is the minimum latitude,
* right is maximum longitude, and top is the maximum latitude.
*/
d3.geo.bounds = function(feature) {
var left = Infinity,
bottom = Infinity,
right = -Infinity,
top = -Infinity;
d3_geo_bounds(feature, function(x, y) {
if (x < left) left = x;
if (x > right) right = x;
if (y < bottom) bottom = y;
if (y > top) top = y;
});
return [[left, bottom], [right, top]];
};
function d3_geo_bounds(o, f) {
if (o.type in d3_geo_boundsTypes) d3_geo_boundsTypes[o.type](o, f);
}
var d3_geo_boundsTypes = {
Feature: d3_geo_boundsFeature,
FeatureCollection: d3_geo_boundsFeatureCollection,
GeometryCollection: d3_geo_boundsGeometryCollection,
LineString: d3_geo_boundsLineString,
MultiLineString: d3_geo_boundsMultiLineString,
MultiPoint: d3_geo_boundsLineString,
MultiPolygon: d3_geo_boundsMultiPolygon,
Point: d3_geo_boundsPoint,
Polygon: d3_geo_boundsPolygon
};
function d3_geo_boundsFeature(o, f) {
d3_geo_bounds(o.geometry, f);
}
function d3_geo_boundsFeatureCollection(o, f) {
for (var a = o.features, i = 0, n = a.length; i < n; i++) {
d3_geo_bounds(a[i].geometry, f);
}
}
function d3_geo_boundsGeometryCollection(o, f) {
for (var a = o.geometries, i = 0, n = a.length; i < n; i++) {
d3_geo_bounds(a[i], f);
}
}
function d3_geo_boundsLineString(o, f) {
for (var a = o.coordinates, i = 0, n = a.length; i < n; i++) {
f.apply(null, a[i]);
}
}
function d3_geo_boundsMultiLineString(o, f) {
for (var a = o.coordinates, i = 0, n = a.length; i < n; i++) {
for (var b = a[i], j = 0, m = b.length; j < m; j++) {
f.apply(null, b[j]);
}
}
}
function d3_geo_boundsMultiPolygon(o, f) {
for (var a = o.coordinates, i = 0, n = a.length; i < n; i++) {
for (var b = a[i][0], j = 0, m = b.length; j < m; j++) {
f.apply(null, b[j]);
}
}
}
function d3_geo_boundsPoint(o, f) {
f.apply(null, o.coordinates);
}
function d3_geo_boundsPolygon(o, f) {
for (var a = o.coordinates[0], i = 0, n = a.length; i < n; i++) {
f.apply(null, a[i]);
}
}
// TODO breakAtDateLine?
d3.geo.circle = function() {
var origin = [0, 0],
degrees = 90 - 1e-2,
radians = degrees * d3_geo_radians,
arc = d3.geo.greatArc().target(Object);
function circle() {
// TODO render a circle as a Polygon
}
function visible(point) {
return arc.distance(point) < radians;
}
circle.clip = function(d) {
arc.source(typeof origin === "function" ? origin.apply(this, arguments) : origin);
return clipType(d);
};
var clipType = d3_geo_type({
FeatureCollection: function(o) {
var features = o.features.map(clipType).filter(Object);
return features && (o = Object.create(o), o.features = features, o);
},
Feature: function(o) {
var geometry = clipType(o.geometry);
return geometry && (o = Object.create(o), o.geometry = geometry, o);
},
Point: function(o) {
return visible(o.coordinates) && o;
},
MultiPoint: function(o) {
var coordinates = o.coordinates.filter(visible);
return coordinates.length && {
type: o.type,
coordinates: coordinates
};
},
LineString: function(o) {
var coordinates = clip(o.coordinates);
return coordinates.length && (o = Object.create(o), o.coordinates = coordinates, o);
},
MultiLineString: function(o) {
var coordinates = o.coordinates.map(clip).filter(function(d) { return d.length; });
return coordinates.length && (o = Object.create(o), o.coordinates = coordinates, o);
},
Polygon: function(o) {
var coordinates = o.coordinates.map(clip);
return coordinates[0].length && (o = Object.create(o), o.coordinates = coordinates, o);
},
MultiPolygon: function(o) {
var coordinates = o.coordinates.map(function(d) { return d.map(clip); }).filter(function(d) { return d[0].length; });
return coordinates.length && (o = Object.create(o), o.coordinates = coordinates, o);
},
GeometryCollection: function(o) {
var geometries = o.geometries.map(clipType).filter(Object);
return geometries.length && (o = Object.create(o), o.geometries = geometries, o);
}
});
function clip(coordinates) {
var i = -1,
n = coordinates.length,
clipped = [],
p0,
p1,
p2,
d0,
d1;
while (++i < n) {
d1 = arc.distance(p2 = coordinates[i]);
if (d1 < radians) {
if (p1) clipped.push(d3_geo_greatArcInterpolate(p1, p2)((d0 - radians) / (d0 - d1)));
clipped.push(p2);
p0 = p1 = null;
} else {
p1 = p2;
if (!p0 && clipped.length) {
clipped.push(d3_geo_greatArcInterpolate(clipped[clipped.length - 1], p1)((radians - d0) / (d1 - d0)));
p0 = p1;
}
}
d0 = d1;
}
if (p1 && clipped.length) {
d1 = arc.distance(p2 = clipped[0]);
clipped.push(d3_geo_greatArcInterpolate(p1, p2)((d0 - radians) / (d0 - d1)));
}
return resample(clipped);
}
// Resample coordinates, creating great arcs between each.
function resample(coordinates) {
var i = 0,
n = coordinates.length,
j,
m,
resampled = n ? [coordinates[0]] : coordinates,
resamples,
origin = arc.source();
while (++i < n) {
resamples = arc.source(coordinates[i - 1])(coordinates[i]).coordinates;
for (j = 0, m = resamples.length; ++j < m;) resampled.push(resamples[j]);
}
arc.source(origin);
return resampled;
}
circle.origin = function(x) {
if (!arguments.length) return origin;
origin = x;
return circle;
};
circle.angle = function(x) {
if (!arguments.length) return degrees;
radians = (degrees = +x) * d3_geo_radians;
return circle;
};
// Precision is specified in degrees.
circle.precision = function(x) {
if (!arguments.length) return arc.precision();
arc.precision(x);
return circle;
};
return circle;
}
d3.geo.greatArc = function() {
var source = d3_geo_greatArcSource,
target = d3_geo_greatArcTarget,
precision = 6 * d3_geo_radians;
function greatArc() {
var a = typeof source === "function" ? source.apply(this, arguments) : source,
b = typeof target === "function" ? target.apply(this, arguments) : target,
i = d3_geo_greatArcInterpolate(a, b),
dt = precision / i.d,
t = 0,
coordinates = [a];
while ((t += dt) < 1) coordinates.push(i(t));
coordinates.push(b);
return {
type: "LineString",
coordinates: coordinates
};
}
// Length returned in radians; multiply by radius for distance.
greatArc.distance = function() {
var a = typeof source === "function" ? source.apply(this, arguments) : source,
b = typeof target === "function" ? target.apply(this, arguments) : target;
return d3_geo_greatArcInterpolate(a, b).d;
};
greatArc.source = function(x) {
if (!arguments.length) return source;
source = x;
return greatArc;
};
greatArc.target = function(x) {
if (!arguments.length) return target;
target = x;
return greatArc;
};
// Precision is specified in degrees.
greatArc.precision = function(x) {
if (!arguments.length) return precision / d3_geo_radians;
precision = x * d3_geo_radians;
return greatArc;
};
return greatArc;
};
function d3_geo_greatArcSource(d) {
return d.source;
}
function d3_geo_greatArcTarget(d) {
return d.target;
}
function d3_geo_greatArcInterpolate(a, b) {
var x0 = a[0] * d3_geo_radians, cx0 = Math.cos(x0), sx0 = Math.sin(x0),
y0 = a[1] * d3_geo_radians, cy0 = Math.cos(y0), sy0 = Math.sin(y0),
x1 = b[0] * d3_geo_radians, cx1 = Math.cos(x1), sx1 = Math.sin(x1),
y1 = b[1] * d3_geo_radians, cy1 = Math.cos(y1), sy1 = Math.sin(y1),
d = interpolate.d = Math.acos(Math.max(-1, Math.min(1, sy0 * sy1 + cy0 * cy1 * Math.cos(x1 - x0)))),
sd = Math.sin(d);
// From http://williams.best.vwh.net/avform.htm#Intermediate
function interpolate(t) {
var A = Math.sin(d - (t *= d)) / sd,
B = Math.sin(t) / sd,
x = A * cy0 * cx0 + B * cy1 * cx1,
y = A * cy0 * sx0 + B * cy1 * sx1,
z = A * sy0 + B * sy1;
return [
Math.atan2(y, x) / d3_geo_radians,
Math.atan2(z, Math.sqrt(x * x + y * y)) / d3_geo_radians
];
}
return interpolate;
}
d3.geo.greatCircle = d3.geo.circle;
})();