Add d3.geoGnomonic.

index.js

@@ -14,6 +14,7 @@ export {default as geoConicConformal} from "./src/projection/conicConformal";
 export {default as geoConicEquidistant} from "./src/projection/conicEquidistant";
 export {default as geoConicEqualArea} from "./src/projection/conicEqualArea";
 export {default as geoEquirectangular} from "./src/projection/equirectangular";
+export {default as geoGnomonic} from "./src/projection/gnomonic";
 export {default as geoProjection, projectionMutator as geoProjectionMutator} from "./src/projection/index";
 export {default as geoMercator} from "./src/projection/mercator";
 export {default as geoOrthographic} from "./src/projection/orthographic";

src/projection/gnomonic.js

@@ -0,0 +1,14 @@
+import {atan, cos, sin} from "../math";
+import {azimuthalInvert} from "./azimuthal";
+import projection from "./index";
+
+function gnomonic(x, y) {
+  var cy = cos(y), k = cos(x) * cy;
+  return [cy * sin(x) / k, sin(y) / k];
+}
+
+gnomonic.invert = azimuthalInvert(atan);
+
+export default function() {
+  return projection(gnomonic);
+}