An approximate inverse for Cahill-Keyes

d3 · May 31, 2020 · 69200f9 · 69200f9
1 parent 01f2242
commit 69200f9
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diff --git a/src/cahillKeyes.js b/src/cahillKeyes.js
@@ -10,6 +10,7 @@ import { abs, cos, degrees, pi, radians, sin, sign, sqrt, tan } from "./math.js"
 import { cartesianCross, cartesianDegrees, cartesianDot, sphericalDegrees } from "./cartesian.js";
 import polyhedral from "./polyhedral/index.js";
 import { geoProjectionMutator as projectionMutator } from "d3-geo";
+import {solve2d} from "./newton.js";
 
 export default function(faceProjection) {
   faceProjection =
@@ -669,6 +670,8 @@ export function cahillKeyesRaw(mg) {
     return mm;
   }
 
+  forward.invert = solve2d(forward);
+
   return forward;
 }
 

diff --git a/test/invert-test.js b/test/invert-test.js
@@ -30,6 +30,19 @@ tape("inverse Imago, tetrahedralLee", function(test) {
   test.end();
 });
 
+tape("inverse Cahill-Keyes", function(test) {
+
+  [ d3.geoCahillKeyes() ]
+  .forEach(function(projection) {
+    [ [-23, 12], [10,10], [100,-45] ]
+    .forEach(function(location) {
+      projection.angle(Math.random()*360);
+      test.projectionEqual(projection, location, projection(location), 1e-5);
+    });
+  });
+  test.end();
+});
+
 tape("inverse complex log", function(test) {
 
   [ d3.geoComplexLog() ]