d3.geo.js

(function(){d3.geo = {};
// 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_radians * origin[0]
      n,
      C,
      p0;

  function albers(coordinates) {
    var t = n * (d3_radians * coordinates[0] - lng0),
        p = Math.sqrt(C - 2 * n * Math.sin(d3_radians * coordinates[1])) / n;
    return [
      scale * p * Math.sin(t) + translate[0],
      scale * (p * Math.cos(t) - p0) + translate[1]
    ];
  }

  function reload() {
    var phi1 = d3_radians * parallels[0],
        phi2 = d3_radians * parallels[1],
        lat0 = d3_radians * origin[1],
        s = Math.sin(phi1),
        c = Math.cos(phi1);
    lng0 = d3_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 < 25
        ? (lon < -100 ? hawaii : puertoRico)
        : (lat > 50 ? alaska : 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());
};

var d3_radians = Math.PI / 180;
d3.geo.mercator = function() {
  var scale = 500,
      translate = [480, 250];

  function mercator(coordinates) {
    var x = (coordinates[0]) / 360,
        y = (-180 / Math.PI * Math.log(Math.tan(Math.PI / 4 + coordinates[1] * Math.PI / 360))) / 360;
    return [
      scale * x + translate[0],
      scale * Math.max(-.5, Math.min(.5, y)) + translate[1]
    ];
  }

  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;
};
/**
 * 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 d3_geo_pathType(pathTypes, d);
  }

  function project(coordinates) {
    return projection(coordinates).join(",");
  }

  var pathTypes = {

    FeatureCollection: function(f) {
      var path = [],
          features = f.features,
          i = -1, // features.index
          n = features.length;
      while (++i < n) path.push(d3_geo_pathType(pathTypes, features[i].geometry));
      return path.join("");
    },

    Feature: function(f) {
      return d3_geo_pathType(pathTypes, f.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;
        m = subcoordinates.length;
        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;
          p = subsubcoordinates.length - 1;
          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(d3_geo_pathType(pathTypes, geometries[i]));
      return path.join("");
    }

  };

  var areaTypes = {

    FeatureCollection: function(f) {
      var area = 0,
          features = f.features,
          i = -1, // features.index
          n = features.length;
      while (++i < n) area += d3_geo_pathType(areaTypes, features[i]);
      return area;
    },

    Feature: function(f) {
      return d3_geo_pathType(areaTypes, f.geometry);
    },

    Point: d3_geo_pathZero,
    MultiPoint: d3_geo_pathZero,
    LineString: d3_geo_pathZero,
    MultiLineString: d3_geo_pathZero,

    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 += d3_geo_pathType(areaTypes, geometries[i]);
      return sum;
    }

  };

  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
        centroid = polygon.centroid(1),
        x = centroid[0],
        y = centroid[1],
        z = Math.abs(polygon.area()),
        i = 0, // coordinates index
        n = coordinates.length;
    while (++i < n) {
      polygon = d3.geom.polygon(coordinates[i].map(projection)); // holes
      centroid = polygon.centroid(1);
      x -= centroid[0];
      y -= centroid[1];
      z -= Math.abs(polygon.area());
    }
    return [x, y, 6 * z]; // weighted centroid
  }

  var centroidTypes = {

    // TODO FeatureCollection
    // TODO Point
    // TODO MultiPoint
    // TODO LineString
    // TODO MultiLineString
    // TODO GeometryCollection

    Feature: function(f) {
      return d3_geo_pathType(centroidTypes, f.geometry);
    },

    Polygon: function(o) {
      var centroid = polygonCentroid(o.coordinates);
      return [centroid[0] / centroid[2], centroid[1] / centroid[2]];
    },

    MultiPolygon: function(o) {
      var area = 0,
          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.area = function(d) {
    return d3_geo_pathType(areaTypes, d);
  };

  path.centroid = function(d) {
    return d3_geo_pathType(centroidTypes, d);
  };

  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";
}

function d3_geo_pathZero() {
  return 0;
}

function d3_geo_pathType(types, o) {
  return o && o.type in types ? types[o.type](o) : "";
}
/**
 * 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,
  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_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]);
  }
}
})()