Sha256: 9139c680c92212c831409a0d15f79a599a9aa406e7c196614c3e1c622ce5e953
Contents?: true
Size: 1.93 KB
Versions: 4
Compression:
Stored size: 1.93 KB
Contents
import "../core/noop";
import "../math/adder";
import "../math/trigonometry";
import "geo";
import "stream";
d3.geo.area = function(object) {
d3_geo_areaSum = 0;
d3.geo.stream(object, d3_geo_area);
return d3_geo_areaSum;
};
var d3_geo_areaSum,
d3_geo_areaRingSum = new d3_adder;
var d3_geo_area = {
sphere: function() { d3_geo_areaSum += 4 * π; },
point: d3_noop,
lineStart: d3_noop,
lineEnd: d3_noop,
// Only count area for polygon rings.
polygonStart: function() {
d3_geo_areaRingSum.reset();
d3_geo_area.lineStart = d3_geo_areaRingStart;
},
polygonEnd: function() {
var area = 2 * d3_geo_areaRingSum;
d3_geo_areaSum += area < 0 ? 4 * π + area : area;
d3_geo_area.lineStart = d3_geo_area.lineEnd = d3_geo_area.point = d3_noop;
}
};
function d3_geo_areaRingStart() {
var λ00, φ00, λ0, cosφ0, sinφ0; // start point and previous point
// For the first point, …
d3_geo_area.point = function(λ, φ) {
d3_geo_area.point = nextPoint;
λ0 = (λ00 = λ) * d3_radians, cosφ0 = Math.cos(φ = (φ00 = φ) * d3_radians / 2 + π / 4), sinφ0 = Math.sin(φ);
};
// For subsequent points, …
function nextPoint(λ, φ) {
λ *= d3_radians;
φ = φ * d3_radians / 2 + π / 4; // half the angular distance from south pole
// Spherical excess E for a spherical triangle with vertices: south pole,
// previous point, current point. Uses a formula derived from Cagnoli’s
// theorem. See Todhunter, Spherical Trig. (1871), Sec. 103, Eq. (2).
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));
// Advance the previous points.
λ0 = λ, cosφ0 = cosφ, sinφ0 = sinφ;
}
// For the last point, return to the start.
d3_geo_area.lineEnd = function() {
nextPoint(λ00, φ00);
};
}
Version data entries
4 entries across 4 versions & 2 rubygems