Using computeIcrfToFixedMatrix breaks panning and 2D view

[Juan Luis Cano]

1. A concise explanation of the problem you're experiencing.

I am using using this function to set a inertial view:

// To have an inertial (ICRF) view
function icrf(scene, time) {
    var icrfToFixed = Cesium.Transforms.computeIcrfToFixedMatrix(time);
    if (Cesium.defined(icrfToFixed)) {
        var camera = viewer.camera;
        var offset = Cesium.Cartesian3.clone(camera.position);
        var transform = Cesium.Matrix4.fromRotationTranslation(icrfToFixed);
        camera.lookAtTransform(transform, offset);
    }
}
viewer.scene.postUpdate.addEventListener(icrf);

However, this has two bad effects:

* When zooming in, panning is more sensitive and I end up moving too much.

* When switching to 2D View, I get an error saying:

An error occurred while rendering.  Rendering has stopped.
undefined
DeveloperError: lookAtTransform is not supported while morphing.
DeveloperError@https://sandcastle.cesium.com/CesiumUnminified/Cesium.js:82:23
Camera.prototype.lookAtTransform@https://sandcastle.cesium.com/CesiumUnminified/Cesium.js:183729:23
icrf@https://sandcastle.cesium.com/templates/bucket.html line 602 > scriptElement:18:16
Event.prototype.raiseEvent@https://sandcastle.cesium.com/CesiumUnminified/Cesium.js:13654:34
Scene.prototype.render@https://sandcastle.cesium.com/CesiumUnminified/Cesium.js:238770:30
CesiumWidget.prototype.render@https://sandcastle.cesium.com/CesiumUnminified/Cesium.js:251493:29
render@https://sandcastle.cesium.com/CesiumUnminified/Cesium.js:250830:36

2. A minimal code example. If you've found a bug, this helps us reproduce and repair it.

https://gist.github.com/Juanlu001/f5c163c689195f9ae26afd58a289def8

3. Context. Why do you need to do this? We might know a better way to accomplish your goal.

I prefer to be able to have an inertial view.

4. The Cesium version you're using, your operating system and browser.

Cesium 1.62 (Cesium Sandcastle), Linux Mint 19.2, Firefox 69.0.3.

[Omar Shehata]

I think you may need to detect and disable the inertial frame logic when the camera is morphing and/or when it's in 2D view. You can listen to the morph event here:

https://cesium.com/docs/cesiumjs-ref-doc/Scene.html?classFilter=scene#morphStart

And detect whether it's in 2D/3D here:

https://cesium.com/docs/cesiumjs-ref-doc/Scene.html?classFilter=scene#mode