Hi there,

**Problem**

I am a bit confused on how Cesium calculates geodetic and geocentric surface normal. Planes, generated from calculated normal do not actually tangent to ellipsoid surface in a given point, more then, the plane created from geodetic surface normal is just the same as one generated from geocentric surface normal.

**Example & why do I need this**

In this Sandcastle XYZ axis along with planes that should be tangent to ellipsoid are drawn when you click on the globe surface.

What I need is to get an XY plane tangent to Ellipsoid at given point and then project other points onto this plane. The problem is as I see the plane is not tangent to ellipsoid at all.

By the way - when I use built in method: ` Cesium.EllipsoidTangentPlane();`

I also get strange result - plane is still not tangent to ellipsoid and also floating somewhere in space. Here is sandcastle.

Appreciate any help because I do not understand what happens here.