Invisible wall at WGS84 elevation zero affecting clipping and zooming

[chris-cooper]

We're having issues rendering geometry and navigating below the WGS84 ellipsoid when terrain is below that level. We prefer not to use underground camera navigation as we still want the camera to stay above the terrain. We require depthTestAgainstTerrain: false (rendering and navigation are more consistent with depthTestAgainstTerrain: true).

1. There is strange clipping behaviour on 'below WGS84 ellipsoid' geometry that should remain visible.

2. There is an invisible wall that prevents a user from zooming the camera in. The wall can be broken through by angling the camera past it as shown in this vid:

Sandcastle example

Browser: Chrome

Operating System: I'm on linux, but I believes the problem occurs on other platforms.

[chris-cooper]

See also #7879

[hpinkos]

@chris-cooper pretty sure this is related to #6840
disableDepthTestDistance is automatically set on billboards that are heightReference: CLAMP_TO_GROUND in an attempt to prevent them from sinking into terrain

[ggetz]

I believe this was all covered by #9200 and #7594.