From 09d8c22d0dc2e2a93c06acd81d16cdfffb6668bb Mon Sep 17 00:00:00 2001
From: Dan Bagnell <daniel.p.bagnell@gmail.com>
Date: Fri, 13 Sep 2013 18:12:58 -0400
Subject: [PATCH] Fix ellipsoid tangent planes for ellipsoids other than the
 unit sphere.

---
 CHANGES.md                              |  1 +
 Source/Core/EllipsoidTangentPlane.js    |  7 +++++--
 Specs/Core/EllipsoidTangentPlaneSpec.js | 26 +++++++++++++++++++++++--
 3 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/CHANGES.md b/CHANGES.md
index 2a57b5ed080f..e4bae3f9b9dc 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -36,6 +36,7 @@ if (defined(p) && defined(p.primitive)) {
 * Added `Scene.sunBloom` to enable/disable the bloom filter on the sun. The bloom filter should be disabled for better frame rates on mobile devices.
 * Fix geometries not closing completely. [#1093](https://github.com/AnalyticalGraphicsInc/cesium/issues/1093)
 * Improved graphics performance.  For example, an Everest terrain view went from 135-140 to over 150 frames per second.
+* Fix `EllipsoidTangentPlane.projectPointOntoPlane` for tangent planes on an ellipsoid other than the unit sphere.
   
 ### b20 - 2013-09-03
 
diff --git a/Source/Core/EllipsoidTangentPlane.js b/Source/Core/EllipsoidTangentPlane.js
index 61c0160add33..4ef58323f9bf 100644
--- a/Source/Core/EllipsoidTangentPlane.js
+++ b/Source/Core/EllipsoidTangentPlane.js
@@ -56,8 +56,7 @@ define([
         this._yAxis = Cartesian3.fromCartesian4(eastNorthUp.getColumn(1));
 
         var normal = Cartesian3.fromCartesian4(eastNorthUp.getColumn(2));
-        var distance = -Cartesian3.dot(origin, origin); //The shortest distance from the origin to the plane.
-        this._plane = new Plane(normal, distance);
+        this._plane = Plane.fromPointNormal(origin, normal);
     };
 
     var tmp = new AxisAlignedBoundingBox();
@@ -119,6 +118,10 @@ define([
         Cartesian3.normalize(cartesian, ray.direction);
 
         var intersectionPoint = IntersectionTests.rayPlane(ray, this._plane, projectPointOntoPlaneCartesian3);
+        if (!defined(intersectionPoint)) {
+            Cartesian3.negate(ray.direction, ray.direction);
+            intersectionPoint = IntersectionTests.rayPlane(ray, this._plane, projectPointOntoPlaneCartesian3);
+        }
 
         if (defined(intersectionPoint)) {
             var v = intersectionPoint.subtract(this._origin, intersectionPoint);
diff --git a/Specs/Core/EllipsoidTangentPlaneSpec.js b/Specs/Core/EllipsoidTangentPlaneSpec.js
index c02f356d90b5..b947c6f4caa5 100644
--- a/Specs/Core/EllipsoidTangentPlaneSpec.js
+++ b/Specs/Core/EllipsoidTangentPlaneSpec.js
@@ -3,12 +3,14 @@ defineSuite([
          'Core/EllipsoidTangentPlane',
          'Core/Ellipsoid',
          'Core/Cartesian2',
-         'Core/Cartesian3'
+         'Core/Cartesian3',
+         'Core/Cartographic'
      ], function(
          EllipsoidTangentPlane,
          Ellipsoid,
          Cartesian2,
-         Cartesian3) {
+         Cartesian3,
+         Cartographic) {
     "use strict";
     /*global jasmine,describe,xdescribe,it,xit,expect,beforeEach,afterEach,beforeAll,afterAll,spyOn,runs,waits,waitsFor*/
 
@@ -167,4 +169,24 @@ defineSuite([
             return tangentPlane.projectPointsOntoEllipsoid(undefined);
         }).toThrow();
     });
+
+    it('projectPointsOntoEllipsoid works with an arbitrary ellipsoid using fromPoints', function () {
+        var ellipsoid = Ellipsoid.WGS84;
+
+        var points = ellipsoid.cartographicArrayToCartesianArray([
+            Cartographic.fromDegrees(-72.0, 40.0),
+            Cartographic.fromDegrees(-68.0, 35.0),
+            Cartographic.fromDegrees(-75.0, 30.0),
+            Cartographic.fromDegrees(-70.0, 30.0),
+            Cartographic.fromDegrees(-68.0, 40.0)
+        ]);
+
+        var tangentPlane = EllipsoidTangentPlane.fromPoints(points, ellipsoid);
+        var points2D = tangentPlane.projectPointsOntoPlane(points);
+        var positionsBack = tangentPlane.projectPointsOntoEllipsoid(points2D);
+
+        expect(positionsBack[0].x).toBeCloseTo(points[0].x);
+        expect(positionsBack[0].y).toBeCloseTo(points[0].y);
+        expect(positionsBack[0].z).toBeCloseTo(points[0].z);
+    });
 });