Robinson: remove unnecessary halfPi, use sign

src/robinson.js

@@ -1,5 +1,5 @@
 import {geoProjection as projection} from "d3-geo";
-import {abs, degrees, epsilon2, floor, halfPi, max, min, pi, radians} from "./math.js";
+import {abs, degrees, epsilon2, floor, max, min, pi, radians, sign} from "./math.js";
 
 var K = [
   [0.9986, -0.062],
@@ -25,7 +25,7 @@ var K = [
 ];
 
 K.forEach(function(d) {
-  d[1] *= 1.0144;
+  d[1] *= 1.593415793900743;
 });
 
 export function robinsonRaw(lambda, phi) {
@@ -41,13 +41,12 @@ export function robinsonRaw(lambda, phi) {
       k;
   return [
     lambda * (bx + di * (cx - ax) / 2 + di * di * (cx - 2 * bx + ax) / 2),
-    (phi > 0 ? halfPi : -halfPi) * (by + di * (cy - ay) / 2 + di * di * (cy - 2 * by + ay) / 2)
+    sign(phi) * (by + di * (cy - ay) / 2 + di * di * (cy - 2 * by + ay) / 2)
   ];
 }
 
 robinsonRaw.invert = function(x, y) {
-  var yy = y / halfPi,
-      phi = yy * 90,
+  var phi = y * 90,
       i = min(18, abs(phi / 5)),
       i0 = max(0, floor(i));
   do {
@@ -56,7 +55,7 @@ robinsonRaw.invert = function(x, y) {
         cy = K[min(19, i0 + 2)][1],
         u = cy - ay,
         v = cy - 2 * by + ay,
-        t = 2 * (abs(yy) - by) / u,
+        t = 2 * (abs(y) - by) / u,
         c = v / u,
         di = t * (1 - c * t * (1 - 2 * c * t));
     if (di >= 0 || i0 === 1) {
@@ -69,7 +68,7 @@ robinsonRaw.invert = function(x, y) {
         ay = K[i0][1];
         by = K[i0 + 1][1];
         cy = K[min(19, i0 + 2)][1];
-        phi -= (delta = (y >= 0 ? halfPi : -halfPi) * (by + di * (cy - ay) / 2 + di * di * (cy - 2 * by + ay) / 2) - y) * degrees;
+        phi -= (delta = sign(y) * (by + di * (cy - ay) / 2 + di * di * (cy - 2 * by + ay) / 2) - y) * degrees;
       } while (abs(delta) > epsilon2 && --j > 0);
       break;
     }