SURFACE

Drawables displayed on the globe's surface, beneath shapes and screen drawables.

Within this group the ordering convention is:

• Double.NEGATIVE_INFINITY — 3D-Tile mesh content (writes GROUND_COVERED_BIT before terrain reads it).

• -Double.MAX_VALUE — terrain depth-only quad (immediately after mesh).

• Other zOrder values — terrain decals (imagery, surface shapes, etc.).