Tile-center geodetic lon/lat (radians) for the per-frame terrain-height query.
Terrain height (m) the tile was baked against; the per-frame offset tracks the delta from this.
Unit ECEF geodetic up at the tile center — the direction the vertical offset is applied along.
Render-time terrain-clamp anchor for a baked tile: the tile is baked once against the terrain height at build time, then GeoScene nudges its whole draw vertically each frame by the delta between the live terrain height under its center and buildHeight — so it conforms continuously as terrain refines, instead of re-baking.