First commit.

Signed-off-by: Chen Xiao <abigwc@gmail.com>

client/node_modules/d3-geo/src/area.js

@@ -0,0 +1,76 @@
+import {Adder} from "d3-array";
+import {atan2, cos, quarterPi, radians, sin, tau} from "./math.js";
+import noop from "./noop.js";
+import stream from "./stream.js";
+
+export var areaRingSum = new Adder();
+
+// hello?
+
+var areaSum = new Adder(),
+    lambda00,
+    phi00,
+    lambda0,
+    cosPhi0,
+    sinPhi0;
+
+export var areaStream = {
+  point: noop,
+  lineStart: noop,
+  lineEnd: noop,
+  polygonStart: function() {
+    areaRingSum = new Adder();
+    areaStream.lineStart = areaRingStart;
+    areaStream.lineEnd = areaRingEnd;
+  },
+  polygonEnd: function() {
+    var areaRing = +areaRingSum;
+    areaSum.add(areaRing < 0 ? tau + areaRing : areaRing);
+    this.lineStart = this.lineEnd = this.point = noop;
+  },
+  sphere: function() {
+    areaSum.add(tau);
+  }
+};
+
+function areaRingStart() {
+  areaStream.point = areaPointFirst;
+}
+
+function areaRingEnd() {
+  areaPoint(lambda00, phi00);
+}
+
+function areaPointFirst(lambda, phi) {
+  areaStream.point = areaPoint;
+  lambda00 = lambda, phi00 = phi;
+  lambda *= radians, phi *= radians;
+  lambda0 = lambda, cosPhi0 = cos(phi = phi / 2 + quarterPi), sinPhi0 = sin(phi);
+}
+
+function areaPoint(lambda, phi) {
+  lambda *= radians, phi *= radians;
+  phi = phi / 2 + quarterPi; // 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 dLambda = lambda - lambda0,
+      sdLambda = dLambda >= 0 ? 1 : -1,
+      adLambda = sdLambda * dLambda,
+      cosPhi = cos(phi),
+      sinPhi = sin(phi),
+      k = sinPhi0 * sinPhi,
+      u = cosPhi0 * cosPhi + k * cos(adLambda),
+      v = k * sdLambda * sin(adLambda);
+  areaRingSum.add(atan2(v, u));
+
+  // Advance the previous points.
+  lambda0 = lambda, cosPhi0 = cosPhi, sinPhi0 = sinPhi;
+}
+
+export default function(object) {
+  areaSum = new Adder();
+  stream(object, areaStream);
+  return areaSum * 2;
+}