Is the Polyline "curvature of the globe" relative to the WGS84 ellipsoid (images included)?

CesiumJS
1

The documentation states the polyline follows the “curvature of the globe”- is this curvature from the WGS84 ellipsoid?

https://cesium.com/learn/cesiumjs/ref-doc/PolylineVolumeGraphics.html

I am drawing a 10km straight line between two points at a constant height above the WGS84 ellipsoid that “follows the curvature of the earth”, yet it does not seem to stay at a constant height relative to the WGS84 ellipsoid… am I misunderstanding something?

Entity (Cartesian3 height of 1290) at Polyline starting position (Cartesian3 height of 1290):

image
image944×1808 43.9 KB

Entity (Cartesian3 height of 1290) at Polyline ending position (Cartestian3 height of 1290):

image
image944×1808 73.7 KB

Entity (Cartesian3 height of 1290) at the middle of the Polyline:

image
image944×1808 75.4 KB

I would’ve thought the height of the PolylineVolume along its full length would be 1290 above the WGS84 ellipsoid? Or am I wrong?

2

Here’s a sandbox. Zoom in and notice the south and north points are located at the bottom of the “tube” and the middle point is smack in the middle of the “tube”.

3

filing this as a bug in github.